introduce lazy values

but I think it's a bad idea, so I'm going to back out the change

6 files changed, 681 insertions, 264 deletions

diff --git a/src/all_types.hpp b/src/all_types.hpp
index efa0bbe1a3..b61a0ba520 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -256,6 +256,7 @@ enum ConstValSpecial {
     ConstValSpecialRuntime,
     ConstValSpecialStatic,
     ConstValSpecialUndef,
+    ConstValSpecialLazy,
 };
 
 enum RuntimeHintErrorUnion {
@@ -291,6 +292,43 @@ struct ConstGlobalRefs {
     LLVMValueRef llvm_global;
 };
 
+enum LazyValueId {
+    LazyValueIdInvalid,
+    LazyValueIdAlignOf,
+    LazyValueIdSliceType,
+    LazyValueIdFnType,
+};
+
+struct LazyValue {
+    LazyValueId id;
+    IrExecutable *exec;
+};
+
+struct LazyValueAlignOf {
+    LazyValue base;
+    ZigType *target_type;
+};
+
+struct LazyValueSliceType {
+    LazyValue base;
+    ZigType *elem_type;
+    ConstExprValue *align_val; // can be null
+    bool is_const;
+    bool is_volatile;
+    bool is_allowzero;
+};
+
+struct LazyValueFnType {
+    LazyValue base;
+    AstNode *proto_node;
+    ConstExprValue **param_types;
+    ConstExprValue *align_val; // can be null
+    ConstExprValue *return_type;
+    ConstExprValue *async_allocator_type;
+    bool is_generic;
+    bool is_var_args;
+};
+
 struct ConstExprValue {
     ZigType *type;
     ConstValSpecial special;
@@ -318,6 +356,7 @@ struct ConstExprValue {
         ConstPtrValue x_ptr;
         ConstArgTuple x_arg_tuple;
         Buf *x_enum_literal;
+        LazyValue *x_lazy;
 
         // populated if special == ConstValSpecialRuntime
         RuntimeHintErrorUnion rh_error_union;
@@ -359,6 +398,7 @@ enum TldResolution {
     TldResolutionUnresolved,
     TldResolutionResolving,
     TldResolutionInvalid,
+    TldResolutionOkLazy,
     TldResolutionOk,
 };
 
@@ -1064,7 +1104,8 @@ struct ZigTypeArray {
 
 struct TypeStructField {
     Buf *name;
-    ZigType *type_entry;
+    ZigType *type_entry; // available after ResolveStatusSizeKnown
+    ConstExprValue *type_val; // available after ResolveStatusZeroBitsKnown
     size_t src_index;
     size_t gen_index;
     size_t offset; // byte offset from beginning of struct
@@ -1893,7 +1934,6 @@ struct ZigVar {
     AstNode *decl_node;
     ZigLLVMDILocalVariable *di_loc_var;
     size_t src_arg_index;
-    size_t gen_arg_index;
     Scope *parent_scope;
     Scope *child_scope;
     LLVMValueRef param_value_ref;
diff --git a/src/analyze.cpp b/src/analyze.cpp
index e17f9eaa66..811d1a1c02 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -19,7 +19,6 @@
 
 static const size_t default_backward_branch_quota = 1000;
 
-static Error resolve_enum_type(CodeGen *g, ZigType *enum_type);
 static Error resolve_struct_type(CodeGen *g, ZigType *struct_type);
 
 static Error ATTRIBUTE_MUST_USE resolve_struct_zero_bits(CodeGen *g, ZigType *struct_type);
@@ -568,12 +567,11 @@ static size_t align_forward(size_t addr, size_t alignment) {
     return (addr + alignment - 1) & ~(alignment - 1);
 }
 
-static size_t next_field_offset(size_t offset, size_t align_from_zero, size_t field_size, size_t field_align) {
-    BREAKPOINT; // TODO test this
+static size_t next_field_offset(size_t offset, size_t align_from_zero, size_t field_size, size_t next_field_align) {
     // Convert offset to a pretend address which has the specified alignment.
     size_t addr = offset + align_from_zero;
     // March the address forward to respect the field alignment.
-    size_t aligned_addr = align_forward(addr + field_size, field_align);
+    size_t aligned_addr = align_forward(addr + field_size, next_field_align);
     // Convert back from pretend address to offset.
     return aligned_addr - align_from_zero;
 }
@@ -623,8 +621,8 @@ ZigType *get_error_union_type(CodeGen *g, ZigType *err_set_type, ZigType *payloa
         field_aligns[err_union_err_index] = err_set_type->abi_align;
         field_sizes[err_union_payload_index] = payload_type->abi_size;
         field_aligns[err_union_payload_index] = payload_type->abi_align;
-        size_t field2_offset = next_field_offset(0, entry->abi_align, field_sizes[0], field_aligns[0]);
-        entry->abi_size = next_field_offset(field2_offset, entry->abi_align, field_sizes[1], field_aligns[1]);
+        size_t field2_offset = next_field_offset(0, entry->abi_align, field_sizes[0], field_aligns[1]);
+        entry->abi_size = next_field_offset(field2_offset, entry->abi_align, field_sizes[1], entry->abi_align);
         entry->size_in_bits = entry->abi_size * 8;
     }
 
@@ -699,6 +697,15 @@ ZigType *get_slice_type(CodeGen *g, ZigType *ptr_type) {
     entry->data.structure.fields_by_name.put(ptr_field_name, &entry->data.structure.fields[slice_ptr_index]);
     entry->data.structure.fields_by_name.put(len_field_name, &entry->data.structure.fields[slice_len_index]);
 
+    switch (type_requires_comptime(g, ptr_type)) {
+        case ReqCompTimeInvalid:
+            zig_unreachable();
+        case ReqCompTimeNo:
+            break;
+        case ReqCompTimeYes:
+            entry->data.structure.requires_comptime = true;
+    }
+
     if (!type_has_bits(ptr_type)) {
         entry->data.structure.gen_field_count = 1;
         entry->data.structure.fields[slice_ptr_index].gen_index = SIZE_MAX;
@@ -897,8 +904,8 @@ ZigType *get_fn_type(CodeGen *g, FnTypeId *fn_type_id) {
 
     fn_type->size_in_bits = g->builtin_types.entry_usize->size_in_bits;
     fn_type->abi_size = g->builtin_types.entry_usize->abi_size;
-    fn_type->abi_align = (fn_type_id->alignment == 0) ?
-        g->builtin_types.entry_usize->abi_align : fn_type_id->alignment;
+    // see also type_val_resolve_abi_align
+    fn_type->abi_align = (fn_type_id->alignment == 0) ? 1 : fn_type_id->alignment;
 
     g->fn_type_table.put(&fn_type->data.fn.fn_type_id, fn_type);
 
@@ -956,15 +963,134 @@ ZigType *get_partial_container_type(CodeGen *g, Scope *scope, ContainerKind kind
     return entry;
 }
 
-static ConstExprValue *analyze_const_value(CodeGen *g, Scope *scope, AstNode *node, ZigType *type_entry,
-        Buf *type_name)
+static ConstExprValue *analyze_const_value_allow_lazy(CodeGen *g, Scope *scope, AstNode *node, ZigType *type_entry,
+        Buf *type_name, bool allow_lazy)
 {
     size_t backward_branch_count = 0;
     return ir_eval_const_value(g, scope, node, type_entry,
             &backward_branch_count, default_backward_branch_quota,
-            nullptr, nullptr, node, type_name, nullptr, nullptr);
+            nullptr, nullptr, node, type_name, nullptr, nullptr, allow_lazy);
 }
 
+static ConstExprValue *analyze_const_value(CodeGen *g, Scope *scope, AstNode *node, ZigType *type_entry,
+        Buf *type_name)
+{
+    return analyze_const_value_allow_lazy(g, scope, node, type_entry, type_name, false);
+}
+
+static Error type_val_resolve_zero_bits(CodeGen *g, ConstExprValue *type_val, bool *is_zero_bits) {
+    Error err;
+    if (type_val->special != ConstValSpecialLazy) {
+        assert(type_val->special == ConstValSpecialStatic);
+        if ((err = type_resolve(g, type_val->data.x_type, ResolveStatusZeroBitsKnown)))
+            return err;
+        *is_zero_bits = (type_val->data.x_type->abi_size == 0);
+        return ErrorNone;
+    }
+    switch (type_val->data.x_lazy->id) {
+        case LazyValueIdInvalid:
+        case LazyValueIdAlignOf:
+            zig_unreachable();
+        case LazyValueIdSliceType:
+            *is_zero_bits = false;
+            return ErrorNone;
+        case LazyValueIdFnType: {
+            LazyValueFnType *lazy_fn_type = reinterpret_cast<LazyValueFnType *>(type_val->data.x_lazy);
+            *is_zero_bits = lazy_fn_type->is_generic;
+            return ErrorNone;
+        }
+    }
+    zig_unreachable();
+}
+
+static Error type_val_resolve_is_opaque_type(CodeGen *g, ConstExprValue *type_val, bool *is_opaque_type) {
+    if (type_val->special != ConstValSpecialLazy) {
+        assert(type_val->special == ConstValSpecialStatic);
+        *is_opaque_type = (type_val->data.x_type->id == ZigTypeIdOpaque);
+        return ErrorNone;
+    }
+    switch (type_val->data.x_lazy->id) {
+        case LazyValueIdInvalid:
+        case LazyValueIdAlignOf:
+            zig_unreachable();
+        case LazyValueIdSliceType:
+        case LazyValueIdFnType:
+            *is_opaque_type = false;
+            return ErrorNone;
+    }
+    zig_unreachable();
+}
+
+static ReqCompTime type_val_resolve_requires_comptime(CodeGen *g, ConstExprValue *type_val) {
+    if (type_val->special != ConstValSpecialLazy) {
+        return type_requires_comptime(g, type_val->data.x_type);
+    }
+    switch (type_val->data.x_lazy->id) {
+        case LazyValueIdInvalid:
+        case LazyValueIdAlignOf:
+            zig_unreachable();
+        case LazyValueIdSliceType: {
+            LazyValueSliceType *lazy_slice_type = reinterpret_cast<LazyValueSliceType *>(type_val->data.x_lazy);
+            return type_requires_comptime(g, lazy_slice_type->elem_type);
+        }
+        case LazyValueIdFnType: {
+            LazyValueFnType *lazy_fn_type = reinterpret_cast<LazyValueFnType *>(type_val->data.x_lazy);
+            if (lazy_fn_type->is_generic)
+                return ReqCompTimeYes;
+            switch (type_val_resolve_requires_comptime(g, lazy_fn_type->return_type)) {
+                case ReqCompTimeInvalid:
+                    return ReqCompTimeInvalid;
+                case ReqCompTimeYes:
+                    return ReqCompTimeYes;
+                case ReqCompTimeNo:
+                    break;
+            }
+            size_t param_count = lazy_fn_type->proto_node->data.fn_proto.params.length;
+            if (lazy_fn_type->is_var_args) param_count -= 1;
+            for (size_t i = 0; i < param_count; i += 1) {
+                switch (type_val_resolve_requires_comptime(g, lazy_fn_type->param_types[i])) {
+                    case ReqCompTimeInvalid:
+                        return ReqCompTimeInvalid;
+                    case ReqCompTimeYes:
+                        return ReqCompTimeYes;
+                    case ReqCompTimeNo:
+                        break;
+                }
+            }
+            return ReqCompTimeNo;
+        }
+    }
+    zig_unreachable();
+}
+
+static Error type_val_resolve_abi_align(CodeGen *g, ConstExprValue *type_val, size_t *abi_align) {
+    Error err;
+    if (type_val->special != ConstValSpecialLazy) {
+        assert(type_val->special == ConstValSpecialStatic);
+        if ((err = type_resolve(g, type_val->data.x_type, ResolveStatusAlignmentKnown)))
+            return err;
+        *abi_align = type_val->data.x_type->abi_align;
+        return ErrorNone;
+    }
+    switch (type_val->data.x_lazy->id) {
+        case LazyValueIdInvalid:
+        case LazyValueIdAlignOf:
+            zig_unreachable();
+        case LazyValueIdSliceType:
+            *abi_align = g->builtin_types.entry_usize->abi_align;
+            return ErrorNone;
+        case LazyValueIdFnType: {
+            LazyValueFnType *lazy_fn_type = reinterpret_cast<LazyValueFnType *>(type_val->data.x_lazy);
+            if (lazy_fn_type->align_val != nullptr)
+                return type_val_resolve_abi_align(g, lazy_fn_type->align_val, abi_align);
+            *abi_align = 1;
+            return ErrorNone;
+        }
+    }
+    zig_unreachable();
+}
+
+
 ZigType *analyze_type_expr(CodeGen *g, Scope *scope, AstNode *node) {
     ConstExprValue *result = analyze_const_value(g, scope, node, g->builtin_types.entry_type, nullptr);
     if (type_is_invalid(result->type))
@@ -1492,11 +1618,6 @@ bool type_is_invalid(ZigType *type_entry) {
 }
 
 
-static Error resolve_enum_type(CodeGen *g, ZigType *enum_type) {
-    return resolve_enum_zero_bits(g, enum_type);
-}
-
-
 ZigType *get_struct_type(CodeGen *g, const char *type_name, const char *field_names[],
         ZigType *field_types[], size_t field_count)
 {
@@ -1536,8 +1657,9 @@ ZigType *get_struct_type(CodeGen *g, const char *type_name, const char *field_na
     for (size_t i = 0; i < field_count; i += 1) {
         TypeStructField *field = &struct_type->data.structure.fields[i];
         field->offset = next_offset;
-        next_offset = next_field_offset(next_offset, abi_align,
-                field->type_entry->abi_size, field->type_entry->abi_align);
+        size_t next_abi_align = (i + 1 == field_count) ?
+            abi_align : struct_type->data.structure.fields[i + 1].type_entry->abi_align;
+        next_offset = next_field_offset(next_offset, abi_align, field->type_entry->abi_size, next_abi_align);
     }
 
     struct_type->abi_align = abi_align;
@@ -1548,7 +1670,7 @@ ZigType *get_struct_type(CodeGen *g, const char *type_name, const char *field_na
 }
 
 static size_t get_store_size_in_bits(size_t size_in_bits) {
-    return (size_in_bits + 7) / 8;
+    return ((size_in_bits + 7) / 8) * 8;
 }
 
 static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
@@ -1584,7 +1706,7 @@ static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
     bool packed = (struct_type->data.structure.layout == ContainerLayoutPacked);
     struct_type->data.structure.resolve_loop_flag = true;
 
-    uint32_t *host_int_bytes = allocate<uint32_t>(struct_type->data.structure.gen_field_count);
+    uint32_t *host_int_bytes = packed ? allocate<uint32_t>(struct_type->data.structure.gen_field_count) : nullptr;
 
     // Compute offsets for all the fields.
     size_t packed_bits_offset = 0;
@@ -1594,24 +1716,53 @@ static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
     size_t size_in_bits = 0;
     size_t abi_align = struct_type->abi_align;
 
+    // Resolve types for fields
     for (size_t i = 0; i < field_count; i += 1) {
-        TypeStructField *type_struct_field = &struct_type->data.structure.fields[i];
-        ZigType *field_type = type_struct_field->type_entry;
+        AstNode *field_source_node = decl_node->data.container_decl.fields.at(i);
+        TypeStructField *field = &struct_type->data.structure.fields[i];
 
-        if (!type_has_bits(field_type))
-            continue;
+        if ((err = ir_resolve_lazy(g, field_source_node, field->type_val))) {
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            return err;
+        }
+        ZigType *field_type = field->type_val->data.x_type;
+        field->type_entry = field_type;
 
         if ((err = type_resolve(g, field_type, ResolveStatusSizeKnown))) {
             struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            return ErrorSemanticAnalyzeFail;
+            return err;
         }
 
         if (struct_type->data.structure.resolve_status == ResolveStatusInvalid) {
             return ErrorSemanticAnalyzeFail;
         }
 
-        type_struct_field->gen_index = gen_field_index;
-        type_struct_field->offset = next_offset;
+        if (packed) {
+            if ((err = emit_error_unless_type_allowed_in_packed_struct(g, field_type, field_source_node))) {
+                struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+                return ErrorSemanticAnalyzeFail;
+            }
+        } else if (struct_type->data.structure.layout == ContainerLayoutExtern &&
+                !type_allowed_in_extern(g, field_type))
+        {
+            add_node_error(g, field_source_node,
+                    buf_sprintf("extern structs cannot contain fields of type '%s'",
+                        buf_ptr(&field_type->name)));
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            return ErrorSemanticAnalyzeFail;
+        }
+    }
+
+    // Calculate offsets
+    for (size_t i = 0; i < field_count; i += 1) {
+        TypeStructField *field = &struct_type->data.structure.fields[i];
+        if (field->gen_index == SIZE_MAX)
+            continue;
+        ZigType *field_type = field->type_entry;
+        assert(field_type != nullptr);
+
+        field->gen_index = gen_field_index;
+        field->offset = next_offset;
 
         if (packed) {
             size_t field_size_in_bits = type_size_bits(g, field_type);
@@ -1621,7 +1772,7 @@ static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
 
             if (first_packed_bits_offset_misalign != SIZE_MAX) {
                 // this field is not byte-aligned; it is part of the previous field with a bit offset
-                type_struct_field->bit_offset_in_host = packed_bits_offset - first_packed_bits_offset_misalign;
+                field->bit_offset_in_host = packed_bits_offset - first_packed_bits_offset_misalign;
 
                 size_t full_bit_count = next_packed_bits_offset - first_packed_bits_offset_misalign;
                 if (get_store_size_in_bits(full_bit_count) == full_bit_count) {
@@ -1636,10 +1787,10 @@ static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
                 }
             } else if (get_store_size_in_bits(field_type->size_in_bits) != field_size_in_bits) {
                 first_packed_bits_offset_misalign = packed_bits_offset;
-                type_struct_field->bit_offset_in_host = 0;
+                field->bit_offset_in_host = 0;
             } else {
                 // This is a byte-aligned field (both start and end) in a packed struct.
-                type_struct_field->bit_offset_in_host = 0;
+                field->bit_offset_in_host = 0;
                 gen_field_index += 1;
                 // TODO: https://github.com/ziglang/zig/issues/1512
                 next_offset = next_field_offset(next_offset, abi_align, field_type->size_in_bits / 8, 1);
@@ -1648,7 +1799,15 @@ static Error resolve_struct_type(CodeGen *g, ZigType *struct_type) {
             packed_bits_offset = next_packed_bits_offset;
         } else {
             gen_field_index += 1;
-            next_offset = next_field_offset(next_offset, abi_align, field_type->abi_size, field_type->abi_align);
+            size_t next_src_field_index = i + 1;
+            for (; next_src_field_index < field_count; next_src_field_index += 1) {
+                if (struct_type->data.structure.fields[next_src_field_index].gen_index != SIZE_MAX) {
+                    break;
+                }
+            }
+            size_t next_abi_align = (next_src_field_index == field_count) ?
+                abi_align : struct_type->data.structure.fields[next_src_field_index].type_entry->abi_align;
+            next_offset = next_field_offset(next_offset, abi_align, field_type->abi_size, next_abi_align);
             size_in_bits = next_offset * 8;
         }
     }
@@ -1679,9 +1838,10 @@ static Error resolve_union_alignment(CodeGen *g, ZigType *union_type) {
         return ErrorSemanticAnalyzeFail;
     if (union_type->data.unionation.resolve_status >= ResolveStatusAlignmentKnown)
         return ErrorNone;
-
     if ((err = resolve_union_zero_bits(g, union_type)))
         return err;
+    if (union_type->data.unionation.resolve_status >= ResolveStatusAlignmentKnown)
+        return ErrorNone;
 
     if (union_type->data.unionation.resolve_loop_flag) {
         if (!union_type->data.unionation.reported_infinite_err) {
@@ -1724,7 +1884,7 @@ static Error resolve_union_alignment(CodeGen *g, ZigType *union_type) {
     }
 
     // unset temporary flag
-    union_type->data.unionation.resolve_loop_flag = true;
+    union_type->data.unionation.resolve_loop_flag = false;
     union_type->data.unionation.resolve_status = ResolveStatusAlignmentKnown;
 
     ZigType *tag_type = union_type->data.unionation.tag_type;
@@ -1836,8 +1996,8 @@ static Error resolve_union_type(CodeGen *g, ZigType *union_type) {
             field_aligns[union_type->data.unionation.gen_tag_index] = tag_type->abi_align;
             field_sizes[union_type->data.unionation.gen_union_index] = union_abi_size;
             field_aligns[union_type->data.unionation.gen_union_index] = most_aligned_union_member->abi_align;
-            size_t field2_offset = next_field_offset(0, union_type->abi_align, field_sizes[0], field_aligns[0]);
-            union_type->abi_size = next_field_offset(field2_offset, union_type->abi_align, field_sizes[1], field_aligns[1]);
+            size_t field2_offset = next_field_offset(0, union_type->abi_align, field_sizes[0], field_aligns[1]);
+            union_type->abi_size = next_field_offset(field2_offset, union_type->abi_align, field_sizes[1], union_type->abi_align);
             union_type->size_in_bits = union_type->abi_size * 8;
         }
     } else {
@@ -1928,6 +2088,9 @@ static Error resolve_enum_zero_bits(CodeGen *g, ZigType *enum_type) {
         }
     }
     enum_type->data.enumeration.tag_int_type = tag_int_type;
+    enum_type->size_in_bits = tag_int_type->size_in_bits;
+    enum_type->abi_size = tag_int_type->abi_size;
+    enum_type->abi_align = tag_int_type->abi_align;
 
     for (uint32_t field_i = 0; field_i < field_count; field_i += 1) {
         AstNode *field_node = decl_node->data.container_decl.fields.at(field_i);
@@ -2012,6 +2175,7 @@ static Error resolve_enum_zero_bits(CodeGen *g, ZigType *enum_type) {
 
     enum_type->data.enumeration.zero_bits_loop_flag = false;
     enum_type->data.enumeration.zero_bits_known = true;
+    enum_type->data.enumeration.complete = true;
 
     if (enum_type->data.enumeration.is_invalid)
         return ErrorSemanticAnalyzeFail;
@@ -2022,22 +2186,28 @@ static Error resolve_enum_zero_bits(CodeGen *g, ZigType *enum_type) {
 static Error resolve_struct_zero_bits(CodeGen *g, ZigType *struct_type) {
     assert(struct_type->id == ZigTypeIdStruct);
 
+    Error err;
+
     if (struct_type->data.structure.resolve_status == ResolveStatusInvalid)
         return ErrorSemanticAnalyzeFail;
     if (struct_type->data.structure.resolve_status >= ResolveStatusZeroBitsKnown)
         return ErrorNone;
 
+    AstNode *decl_node = struct_type->data.structure.decl_node;
+    assert(decl_node->type == NodeTypeContainerDecl);
+
     if (struct_type->data.structure.resolve_loop_flag) {
-        struct_type->data.structure.resolve_status = ResolveStatusZeroBitsKnown;
-        struct_type->data.structure.resolve_loop_flag = false;
-        return ErrorNone;
+        if (struct_type->data.structure.resolve_status != ResolveStatusInvalid) {
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            ErrorMsg *msg = add_node_error(g, decl_node,
+                buf_sprintf("struct '%s' depends on its own size", buf_ptr(&struct_type->name)));
+            emit_error_notes_for_ref_stack(g, msg);
+        }
+        return ErrorSemanticAnalyzeFail;
     }
 
     struct_type->data.structure.resolve_loop_flag = true;
 
-    AstNode *decl_node = struct_type->data.structure.decl_node;
-    assert(decl_node->type == NodeTypeContainerDecl);
-
     assert(!struct_type->data.structure.fields);
     size_t field_count = decl_node->data.container_decl.fields.length;
     struct_type->data.structure.src_field_count = (uint32_t)field_count;
@@ -2056,7 +2226,7 @@ static Error resolve_struct_zero_bits(CodeGen *g, ZigType *struct_type) {
         if (field_node->data.struct_field.type == nullptr) {
             add_node_error(g, field_node, buf_sprintf("struct field missing type"));
             struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            continue;
+            return ErrorSemanticAnalyzeFail;
         }
 
         auto field_entry = struct_type->data.structure.fields_by_name.put_unique(type_struct_field->name, type_struct_field);
@@ -2065,38 +2235,55 @@ static Error resolve_struct_zero_bits(CodeGen *g, ZigType *struct_type) {
                 buf_sprintf("duplicate struct field: '%s'", buf_ptr(type_struct_field->name)));
             add_error_note(g, msg, field_entry->value->decl_node, buf_sprintf("other field here"));
             struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            continue;
+            return ErrorSemanticAnalyzeFail;
         }
 
-        ZigType *field_type = analyze_type_expr(g, scope, field_node->data.struct_field.type);
-        type_struct_field->type_entry = field_type;
+        ConstExprValue *field_type_val = analyze_const_value_allow_lazy(g, scope,
+                field_node->data.struct_field.type, g->builtin_types.entry_type, nullptr, true);
+        if (type_is_invalid(field_type_val->type)) {
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            return ErrorSemanticAnalyzeFail;
+        }
+        assert(field_type_val->special != ConstValSpecialRuntime);
+        type_struct_field->type_val = field_type_val;
         type_struct_field->src_index = i;
         type_struct_field->gen_index = SIZE_MAX;
 
+        if (struct_type->data.structure.resolve_status == ResolveStatusInvalid)
+            return ErrorSemanticAnalyzeFail;
+
         if (field_node->data.struct_field.value != nullptr) {
             add_node_error(g, field_node->data.struct_field.value,
                     buf_sprintf("enums, not structs, support field assignment"));
         }
-
-        if (field_type->id == ZigTypeIdOpaque) {
+        bool field_is_opaque_type;
+        if ((err = type_val_resolve_is_opaque_type(g, field_type_val, &field_is_opaque_type))) {
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            return ErrorSemanticAnalyzeFail;
+        }
+        if (field_is_opaque_type) {
             add_node_error(g, field_node->data.struct_field.type,
                 buf_sprintf("opaque types have unknown size and therefore cannot be directly embedded in structs"));
             struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            continue;
+            return ErrorSemanticAnalyzeFail;
         }
-
-        switch (type_requires_comptime(g, field_type)) {
+        switch (type_val_resolve_requires_comptime(g, field_type_val)) {
             case ReqCompTimeYes:
                 struct_type->data.structure.requires_comptime = true;
                 break;
             case ReqCompTimeInvalid:
                 struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-                continue;
+                return ErrorSemanticAnalyzeFail;
             case ReqCompTimeNo:
                 break;
         }
 
-        if (!type_has_bits(field_type))
+        bool field_is_zero_bits;
+        if ((err = type_val_resolve_zero_bits(g, field_type_val, &field_is_zero_bits))) {
+            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+            return ErrorSemanticAnalyzeFail;
+        }
+        if (field_is_zero_bits)
             continue;
 
         type_struct_field->gen_index = gen_field_index;
@@ -2126,9 +2313,10 @@ static Error resolve_struct_alignment(CodeGen *g, ZigType *struct_type) {
         return ErrorSemanticAnalyzeFail;
     if (struct_type->data.structure.resolve_status >= ResolveStatusAlignmentKnown)
         return ErrorNone;
-
     if ((err = resolve_struct_zero_bits(g, struct_type)))
         return err;
+    if (struct_type->data.structure.resolve_status >= ResolveStatusAlignmentKnown)
+        return ErrorNone;
 
     AstNode *decl_node = struct_type->data.structure.decl_node;
 
@@ -2136,7 +2324,7 @@ static Error resolve_struct_alignment(CodeGen *g, ZigType *struct_type) {
         if (struct_type->data.structure.resolve_status != ResolveStatusInvalid) {
             struct_type->data.structure.resolve_status = ResolveStatusInvalid;
             ErrorMsg *msg = add_node_error(g, decl_node,
-                buf_sprintf("struct '%s' contains itself", buf_ptr(&struct_type->name)));
+                buf_sprintf("struct '%s' depends on its own alignment", buf_ptr(&struct_type->name)));
             emit_error_notes_for_ref_stack(g, msg);
         }
         return ErrorSemanticAnalyzeFail;
@@ -2151,42 +2339,23 @@ static Error resolve_struct_alignment(CodeGen *g, ZigType *struct_type) {
 
     for (size_t i = 0; i < field_count; i += 1) {
         TypeStructField *field = &struct_type->data.structure.fields[i];
-        ZigType *field_type = field->type_entry;
-        assert(field_type != nullptr);
-
-        if ((err = type_resolve(g, field_type, ResolveStatusAlignmentKnown))) {
-            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            return ErrorSemanticAnalyzeFail;
-        }
-
-        if (struct_type->data.structure.layout == ContainerLayoutExtern &&
-            !type_allowed_in_extern(g, field_type))
-        {
-            AstNode *field_source_node = decl_node->data.container_decl.fields.at(i);
-            add_node_error(g, field_source_node,
-                    buf_sprintf("extern structs cannot contain fields of type '%s'",
-                        buf_ptr(&field_type->name)));
-            struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-            return ErrorSemanticAnalyzeFail;
-        }
-
-        if (!type_has_bits(field_type))
+        if (field->gen_index == SIZE_MAX)
             continue;
 
         if (packed) {
-            AstNode *field_source_node = decl_node->data.container_decl.fields.at(i);
-            if ((err = emit_error_unless_type_allowed_in_packed_struct(g, field_type, field_source_node))) {
-                struct_type->data.structure.resolve_status = ResolveStatusInvalid;
-                return ErrorSemanticAnalyzeFail;
-            }
             // TODO: https://github.com/ziglang/zig/issues/1512
             if (1 > abi_align) {
                 abi_align = 1;
             }
         } else {
             // TODO: https://github.com/ziglang/zig/issues/1512
-            if (field_type->abi_align > abi_align) {
-                abi_align = field_type->abi_align;
+            size_t field_align;
+            if ((err = type_val_resolve_abi_align(g, field->type_val, &field_align))) {
+                struct_type->data.structure.resolve_status = ResolveStatusInvalid;
+                return err;
+            }
+            if (field_align > abi_align) {
+                abi_align = field_align;
             }
         }
     }
@@ -2824,7 +2993,7 @@ void init_tld(Tld *tld, TldId id, Buf *name, VisibMod visib_mod, AstNode *source
 
 void update_compile_var(CodeGen *g, Buf *name, ConstExprValue *value) {
     Tld *tld = get_container_scope(g->compile_var_import)->decl_table.get(name);
-    resolve_top_level_decl(g, tld, tld->source_node);
+    resolve_top_level_decl(g, tld, tld->source_node, false);
     assert(tld->id == TldIdVar);
     TldVar *tld_var = (TldVar *)tld;
     tld_var->var->const_value = value;
@@ -2933,20 +3102,17 @@ void scan_decls(CodeGen *g, ScopeDecls *decls_scope, AstNode *node) {
     }
 }
 
-static void resolve_decl_container(CodeGen *g, TldContainer *tld_container) {
+static Error resolve_decl_container(CodeGen *g, TldContainer *tld_container) {
     ZigType *type_entry = tld_container->type_entry;
     assert(type_entry);
 
     switch (type_entry->id) {
         case ZigTypeIdStruct:
-            resolve_struct_type(g, tld_container->type_entry);
-            return;
+            return resolve_struct_type(g, tld_container->type_entry);
         case ZigTypeIdEnum:
-            resolve_enum_type(g, tld_container->type_entry);
-            return;
+            return resolve_enum_zero_bits(g, tld_container->type_entry);
         case ZigTypeIdUnion:
-            resolve_union_type(g, tld_container->type_entry);
-            return;
+            return resolve_union_type(g, tld_container->type_entry);
         default:
             zig_unreachable();
     }
@@ -3066,7 +3232,7 @@ ZigVar *add_variable(CodeGen *g, AstNode *source_node, Scope *parent_scope, Buf
     return variable_entry;
 }
 
-static void resolve_decl_var(CodeGen *g, TldVar *tld_var) {
+static void resolve_decl_var(CodeGen *g, TldVar *tld_var, bool allow_lazy) {
     AstNode *source_node = tld_var->base.source_node;
     AstNodeVariableDeclaration *var_decl = &source_node->data.variable_declaration;
 
@@ -3107,7 +3273,8 @@ static void resolve_decl_var(CodeGen *g, TldVar *tld_var) {
     if (explicit_type && explicit_type->id == ZigTypeIdInvalid) {
         implicit_type = explicit_type;
     } else if (var_decl->expr) {
-        init_value = analyze_const_value(g, tld_var->base.parent_scope, var_decl->expr, explicit_type, var_decl->symbol);
+        init_value = analyze_const_value_allow_lazy(g, tld_var->base.parent_scope, var_decl->expr,
+                explicit_type, var_decl->symbol, allow_lazy);
         assert(init_value);
         implicit_type = init_value->type;
 
@@ -3170,11 +3337,11 @@ static void resolve_decl_var(CodeGen *g, TldVar *tld_var) {
     g->global_vars.append(tld_var);
 }
 
-void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node) {
-    if (tld->resolution != TldResolutionUnresolved)
+void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node, bool allow_lazy) {
+    bool want_resolve_lazy = tld->resolution == TldResolutionOkLazy && !allow_lazy;
+    if (tld->resolution != TldResolutionUnresolved && !want_resolve_lazy)
         return;
 
-    assert(tld->resolution != TldResolutionResolving);
     tld->resolution = TldResolutionResolving;
     g->tld_ref_source_node_stack.append(source_node);
 
@@ -3182,7 +3349,11 @@ void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node) {
         case TldIdVar:
             {
                 TldVar *tld_var = (TldVar *)tld;
-                resolve_decl_var(g, tld_var);
+                if (want_resolve_lazy) {
+                    ir_resolve_lazy(g, source_node, tld_var->var->const_value);
+                } else {
+                    resolve_decl_var(g, tld_var, allow_lazy);
+                }
                 break;
             }
         case TldIdFn:
@@ -3205,7 +3376,7 @@ void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node) {
             }
     }
 
-    tld->resolution = TldResolutionOk;
+    tld->resolution = allow_lazy ? TldResolutionOkLazy : TldResolutionOk;
     g->tld_ref_source_node_stack.pop();
 }
 
@@ -3399,17 +3570,14 @@ ZigType *container_ref_type(ZigType *type_entry) {
         type_entry->data.pointer.child_type : type_entry;
 }
 
-void resolve_container_type(CodeGen *g, ZigType *type_entry) {
+Error resolve_container_type(CodeGen *g, ZigType *type_entry) {
     switch (type_entry->id) {
         case ZigTypeIdStruct:
-            resolve_struct_type(g, type_entry);
-            break;
+            return resolve_struct_type(g, type_entry);
         case ZigTypeIdEnum:
-            resolve_enum_type(g, type_entry);
-            break;
+            return resolve_enum_zero_bits(g, type_entry);
         case ZigTypeIdUnion:
-            resolve_union_type(g, type_entry);
-            break;
+            return resolve_union_type(g, type_entry);
         case ZigTypeIdPointer:
         case ZigTypeIdMetaType:
         case ZigTypeIdVoid:
@@ -3435,6 +3603,7 @@ void resolve_container_type(CodeGen *g, ZigType *type_entry) {
         case ZigTypeIdVector:
             zig_unreachable();
     }
+    zig_unreachable();
 }
 
 ZigType *get_src_ptr_type(ZigType *type) {
@@ -3536,10 +3705,6 @@ static void define_local_param_variables(CodeGen *g, ZigFn *fn_table_entry) {
         if (type_has_bits(param_type)) {
             fn_table_entry->variable_list.append(var);
         }
-
-        if (fn_type->data.fn.gen_param_info) {
-            var->gen_arg_index = fn_type->data.fn.gen_param_info[i].gen_index;
-        }
     }
 }
 
@@ -3880,7 +4045,7 @@ void semantic_analyze(CodeGen *g) {
         for (; g->resolve_queue_index < g->resolve_queue.length; g->resolve_queue_index += 1) {
             Tld *tld = g->resolve_queue.at(g->resolve_queue_index);
             AstNode *source_node = nullptr;
-            resolve_top_level_decl(g, tld, source_node);
+            resolve_top_level_decl(g, tld, source_node, false);
         }
 
         for (; g->fn_defs_index < g->fn_defs.length; g->fn_defs_index += 1) {
@@ -4941,7 +5106,7 @@ Error type_resolve(CodeGen *g, ZigType *ty, ResolveStatus status) {
             if (ty->id == ZigTypeIdStruct) {
                 return resolve_struct_type(g, ty);
             } else if (ty->id == ZigTypeIdEnum) {
-                return resolve_enum_type(g, ty);
+                return resolve_enum_zero_bits(g, ty);
             } else if (ty->id == ZigTypeIdUnion) {
                 return resolve_union_type(g, ty);
             }
@@ -5314,6 +5479,9 @@ void render_const_value(CodeGen *g, Buf *buf, ConstExprValue *const_val) {
         case ConstValSpecialRuntime:
             buf_appendf(buf, "(runtime value)");
             return;
+        case ConstValSpecialLazy:
+            buf_appendf(buf, "(lazy value)");
+            return;
         case ConstValSpecialUndef:
             buf_appendf(buf, "undefined");
             return;
@@ -5930,7 +6098,7 @@ bool type_ptr_eql(const ZigType *a, const ZigType *b) {
 
 ConstExprValue *get_builtin_value(CodeGen *codegen, const char *name) {
     Tld *tld = get_container_scope(codegen->compile_var_import)->decl_table.get(buf_create_from_str(name));
-    resolve_top_level_decl(codegen, tld, nullptr);
+    resolve_top_level_decl(codegen, tld, nullptr, false);
     assert(tld->id == TldIdVar);
     TldVar *tld_var = (TldVar *)tld;
     ConstExprValue *var_value = tld_var->var->const_value;
@@ -6114,6 +6282,8 @@ bool type_is_c_abi_int(CodeGen *g, ZigType *ty) {
 uint32_t get_host_int_bytes(CodeGen *g, ZigType *struct_type, TypeStructField *field) {
     assert(struct_type->id == ZigTypeIdStruct);
     assert(type_is_resolved(struct_type, ResolveStatusSizeKnown));
+    if (struct_type->data.structure.host_int_bytes == nullptr)
+        return 0;
     return struct_type->data.structure.host_int_bytes[field->gen_index];
 }
 
@@ -6374,8 +6544,13 @@ static void resolve_llvm_types_struct(CodeGen *g, ZigType *struct_type) {
     LLVMStructSetBody(struct_type->llvm_type, element_types, (unsigned)gen_field_count, packed);
 
     ZigLLVMDIType **di_element_types = allocate<ZigLLVMDIType*>(debug_field_count);
-
     ZigType *import = get_scope_import(scope);
+    unsigned dwarf_kind = ZigLLVMTag_DW_structure_type();
+    struct_type->llvm_di_type = ZigLLVMCreateReplaceableCompositeType(g->dbuilder,
+        dwarf_kind, buf_ptr(&struct_type->name),
+        ZigLLVMFileToScope(import->data.structure.root_struct->di_file),
+        import->data.structure.root_struct->di_file, (unsigned)(decl_node->line + 1));
+
     size_t debug_field_index = 0;
     for (size_t i = 0; i < field_count; i += 1) {
         AstNode *field_node = decl_node->data.container_decl.fields.at(i);
diff --git a/src/analyze.hpp b/src/analyze.hpp
index 02f453ae8c..48f07fd633 100644
--- a/src/analyze.hpp
+++ b/src/analyze.hpp
@@ -61,7 +61,7 @@ ZigType *add_source_file(CodeGen *g, ZigPackage *package, Buf *abs_full_path, Bu
 ZigVar *find_variable(CodeGen *g, Scope *orig_context, Buf *name, ScopeFnDef **crossed_fndef_scope);
 Tld *find_decl(CodeGen *g, Scope *scope, Buf *name);
 Tld *find_container_decl(CodeGen *g, ScopeDecls *decls_scope, Buf *name);
-void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node);
+void resolve_top_level_decl(CodeGen *g, Tld *tld, AstNode *source_node, bool allow_lazy);
 
 ZigType *get_src_ptr_type(ZigType *type);
 ZigType *get_codegen_ptr_type(ZigType *type);
@@ -73,7 +73,7 @@ bool type_is_complete(ZigType *type_entry);
 bool type_is_resolved(ZigType *type_entry, ResolveStatus status);
 bool type_is_invalid(ZigType *type_entry);
 bool type_is_global_error_set(ZigType *err_set_type);
-void resolve_container_type(CodeGen *g, ZigType *type_entry);
+Error resolve_container_type(CodeGen *g, ZigType *type_entry);
 ScopeDecls *get_container_scope(ZigType *type_entry);
 TypeStructField *find_struct_type_field(ZigType *type_entry, Buf *name);
 TypeEnumField *find_enum_type_field(ZigType *enum_type, Buf *name);
@@ -246,4 +246,5 @@ Error create_c_object_cache(CodeGen *g, CacheHash **out_cache_hash, bool verbose
 
 LLVMTypeRef get_llvm_type(CodeGen *g, ZigType *type);
 ZigLLVMDIType *get_llvm_di_type(CodeGen *g, ZigType *type);
+
 #endif
diff --git a/src/codegen.cpp b/src/codegen.cpp
index b7adae798c..f5b15bbeb4 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -483,6 +483,8 @@ static LLVMValueRef fn_llvm_value(CodeGen *g, ZigFn *fn_table_entry) {
 
 
     ZigType *fn_type = fn_table_entry->type_entry;
+    // Make the raw_type_ref populated
+    (void)get_llvm_type(g, fn_type);
     LLVMTypeRef fn_llvm_type = fn_type->data.fn.raw_type_ref;
     if (fn_table_entry->body_node == nullptr) {
         LLVMValueRef existing_llvm_fn = LLVMGetNamedFunction(g->module, buf_ptr(symbol_name));
@@ -2285,7 +2287,9 @@ void walk_function_params(CodeGen *g, ZigType *fn_type, FnWalk *fn_walk) {
 
                 if (!handle_is_ptr(variable->var_type)) {
                     clear_debug_source_node(g);
-                    gen_store_untyped(g, LLVMGetParam(llvm_fn, (unsigned)variable->gen_arg_index),
+                    ZigType *fn_type = fn_table_entry->type_entry;
+                    unsigned gen_arg_index = fn_type->data.fn.gen_param_info[variable->src_arg_index].gen_index;
+                    gen_store_untyped(g, LLVMGetParam(llvm_fn, gen_arg_index),
                             variable->value_ref, variable->align_bytes, false);
                 }
 
@@ -3354,6 +3358,8 @@ static bool value_is_all_undef_array(ConstExprValue *const_val, size_t len) {
 
 static bool value_is_all_undef(ConstExprValue *const_val) {
     switch (const_val->special) {
+        case ConstValSpecialLazy:
+            zig_unreachable();
         case ConstValSpecialRuntime:
             return false;
         case ConstValSpecialUndef:
@@ -5818,6 +5824,7 @@ static LLVMValueRef gen_const_ptr_union_recursive(CodeGen *g, ConstExprValue *un
 
 static LLVMValueRef pack_const_int(CodeGen *g, LLVMTypeRef big_int_type_ref, ConstExprValue *const_val) {
     switch (const_val->special) {
+        case ConstValSpecialLazy:
         case ConstValSpecialRuntime:
             zig_unreachable();
         case ConstValSpecialUndef:
@@ -6075,6 +6082,7 @@ static LLVMValueRef gen_const_val(CodeGen *g, ConstExprValue *const_val, const c
     assert(type_has_bits(type_entry));
 
     switch (const_val->special) {
+        case ConstValSpecialLazy:
         case ConstValSpecialRuntime:
             zig_unreachable();
         case ConstValSpecialUndef:
@@ -6834,9 +6842,9 @@ static void do_code_gen(CodeGen *g) {
                 fn_walk_var.data.vars.var = var;
                 iter_function_params_c_abi(g, fn_table_entry->type_entry, &fn_walk_var, var->src_arg_index);
             } else {
-                assert(var->gen_arg_index != SIZE_MAX);
                 ZigType *gen_type;
                 FnGenParamInfo *gen_info = &fn_table_entry->type_entry->data.fn.gen_param_info[var->src_arg_index];
+                assert(gen_info->gen_index != SIZE_MAX);
 
                 if (handle_is_ptr(var->var_type)) {
                     if (gen_info->is_byval) {
@@ -6844,7 +6852,7 @@ static void do_code_gen(CodeGen *g) {
                     } else {
                         gen_type = gen_info->type;
                     }
-                    var->value_ref = LLVMGetParam(fn, (unsigned)var->gen_arg_index);
+                    var->value_ref = LLVMGetParam(fn, gen_info->gen_index);
                 } else {
                     gen_type = var->var_type;
                     var->value_ref = build_alloca(g, var->var_type, buf_ptr(&var->name), var->align_bytes);
@@ -6853,7 +6861,7 @@ static void do_code_gen(CodeGen *g) {
                     var->di_loc_var = ZigLLVMCreateParameterVariable(g->dbuilder, get_di_scope(g, var->parent_scope),
                             buf_ptr(&var->name), import->data.structure.root_struct->di_file,
                             (unsigned)(var->decl_node->line + 1),
-                            get_llvm_di_type(g, gen_type), !g->strip_debug_symbols, 0, (unsigned)(var->gen_arg_index + 1));
+                            get_llvm_di_type(g, gen_type), !g->strip_debug_symbols, 0, (unsigned)(gen_info->gen_index));
                 }
 
             }
@@ -8241,7 +8249,7 @@ static void gen_root_source(CodeGen *g) {
         }
         Tld *panic_tld = find_decl(g, &get_container_scope(import_with_panic)->base, buf_create_from_str("panic"));
         assert(panic_tld != nullptr);
-        resolve_top_level_decl(g, panic_tld, nullptr);
+        resolve_top_level_decl(g, panic_tld, nullptr, false);
     }
 
 
diff --git a/src/ir.cpp b/src/ir.cpp
index 872a943814..a4d7cf271b 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -154,6 +154,7 @@ struct ConstCastBadAllowsZero {
 enum UndefAllowed {
     UndefOk,
     UndefBad,
+    LazyOk,
 };
 
 static IrInstruction *ir_gen_node(IrBuilder *irb, AstNode *node, Scope *scope);
@@ -10256,32 +10257,57 @@ static IrInstruction *ir_get_const_ptr(IrAnalyze *ira, IrInstruction *instructio
     return const_instr;
 }
 
+static Error ir_resolve_const_val(CodeGen *codegen, IrExecutable *exec, AstNode *source_node,
+        ConstExprValue *val, UndefAllowed undef_allowed)
+{
+    Error err;
+    for (;;) {
+        switch (val->special) {
+            case ConstValSpecialStatic:
+                return ErrorNone;
+            case ConstValSpecialRuntime:
+                if (!type_has_bits(val->type))
+                    return ErrorNone;
+
+                exec_add_error_node(codegen, exec, source_node,
+                        buf_sprintf("unable to evaluate constant expression"));
+                return ErrorSemanticAnalyzeFail;
+            case ConstValSpecialUndef:
+                if (undef_allowed == UndefOk)
+                    return ErrorNone;
+
+                exec_add_error_node(codegen, exec, source_node,
+                        buf_sprintf("use of undefined value here causes undefined behavior"));
+                return ErrorSemanticAnalyzeFail;
+            case ConstValSpecialLazy:
+                if (undef_allowed == LazyOk)
+                    return ErrorNone;
+
+                if ((err = ir_resolve_lazy(codegen, source_node, val)))
+                    return err;
+
+                continue;
+        }
+    }
+}
+
 static ConstExprValue *ir_resolve_const(IrAnalyze *ira, IrInstruction *value, UndefAllowed undef_allowed) {
-    switch (value->value.special) {
-        case ConstValSpecialStatic:
-            return &value->value;
-        case ConstValSpecialRuntime:
-            if (!type_has_bits(value->value.type)) {
-                return &value->value;
-            }
-            ir_add_error(ira, value, buf_sprintf("unable to evaluate constant expression"));
-            return nullptr;
-        case ConstValSpecialUndef:
-            if (undef_allowed == UndefOk) {
-                return &value->value;
-            } else {
-                ir_add_error(ira, value, buf_sprintf("use of undefined value here causes undefined behavior"));
-                return nullptr;
-            }
+    Error err;
+    if ((err = ir_resolve_const_val(ira->codegen, ira->new_irb.exec, value->source_node,
+                    &value->value, undef_allowed)))
+    {
+        return nullptr;
     }
-    zig_unreachable();
+    return &value->value;
 }
 
 ConstExprValue *ir_eval_const_value(CodeGen *codegen, Scope *scope, AstNode *node,
         ZigType *expected_type, size_t *backward_branch_count, size_t backward_branch_quota,
         ZigFn *fn_entry, Buf *c_import_buf, AstNode *source_node, Buf *exec_name,
-        IrExecutable *parent_exec, AstNode *expected_type_source_node)
+        IrExecutable *parent_exec, AstNode *expected_type_source_node, bool allow_lazy)
 {
+    Error err;
+
     if (expected_type != nullptr && type_is_invalid(expected_type))
         return &codegen->invalid_instruction->value;
 
@@ -10326,7 +10352,24 @@ ConstExprValue *ir_eval_const_value(CodeGen *codegen, Scope *scope, AstNode *nod
         fprintf(stderr, "}\n");
     }
 
-    return ir_exec_const_result(codegen, analyzed_executable);
+    ConstExprValue *result = ir_exec_const_result(codegen, analyzed_executable);
+
+    if (!allow_lazy) {
+        if ((err = ir_resolve_lazy(codegen, node, result)))
+            return &codegen->invalid_instruction->value;
+    }
+    return result;
+}
+
+static ZigType *ir_resolve_const_type(CodeGen *codegen, IrExecutable *exec, AstNode *source_node,
+        ConstExprValue *val)
+{
+    Error err;
+    if ((err = ir_resolve_const_val(codegen, exec, source_node, val, UndefBad)))
+        return codegen->builtin_types.entry_invalid;
+
+    assert(val->data.x_type != nullptr);
+    return val->data.x_type;
 }
 
 static ZigType *ir_resolve_type(IrAnalyze *ira, IrInstruction *type_value) {
@@ -10339,12 +10382,7 @@ static ZigType *ir_resolve_type(IrAnalyze *ira, IrInstruction *type_value) {
         return ira->codegen->builtin_types.entry_invalid;
     }
 
-    ConstExprValue *const_val = ir_resolve_const(ira, type_value, UndefBad);
-    if (!const_val)
-        return ira->codegen->builtin_types.entry_invalid;
-
-    assert(const_val->data.x_type != nullptr);
-    return const_val->data.x_type;
+    return ir_resolve_const_type(ira->codegen, ira->new_irb.exec, type_value->source_node, &type_value->value);
 }
 
 static ZigType *ir_resolve_error_set_type(IrAnalyze *ira, IrInstruction *op_source, IrInstruction *type_value) {
@@ -11835,33 +11873,38 @@ static IrInstruction *ir_get_deref(IrAnalyze *ira, IrInstruction *source_instruc
     }
 }
 
-static bool ir_resolve_align(IrAnalyze *ira, IrInstruction *value, uint32_t *out) {
-    if (type_is_invalid(value->value.type))
-        return false;
-
-    IrInstruction *casted_value = ir_implicit_cast(ira, value, get_align_amt_type(ira->codegen));
-    if (type_is_invalid(casted_value->value.type))
-        return false;
-
-    ConstExprValue *const_val = ir_resolve_const(ira, casted_value, UndefBad);
-    if (!const_val)
+static bool ir_resolve_const_align(CodeGen *codegen, IrExecutable *exec, AstNode *source_node,
+        ConstExprValue *const_val, uint32_t *out)
+{
+    Error err;
+    if ((err = ir_resolve_const_val(codegen, exec, source_node, const_val, UndefBad)))
         return false;
 
     uint32_t align_bytes = bigint_as_unsigned(&const_val->data.x_bigint);
     if (align_bytes == 0) {
-        ir_add_error(ira, value, buf_sprintf("alignment must be >= 1"));
+        exec_add_error_node(codegen, exec, source_node, buf_sprintf("alignment must be >= 1"));
         return false;
     }
 
     if (!is_power_of_2(align_bytes)) {
-        ir_add_error(ira, value, buf_sprintf("alignment value %" PRIu32 " is not a power of 2", align_bytes));
+        exec_add_error_node(codegen, exec, source_node, buf_sprintf("alignment value %" PRIu32 " is not a power of 2", align_bytes));
         return false;
     }
-
     *out = align_bytes;
     return true;
 }
 
+static bool ir_resolve_align(IrAnalyze *ira, IrInstruction *value, uint32_t *out) {
+    if (type_is_invalid(value->value.type))
+        return false;
+
+    IrInstruction *casted_value = ir_implicit_cast(ira, value, get_align_amt_type(ira->codegen));
+    if (type_is_invalid(casted_value->value.type))
+        return false;
+
+    return ir_resolve_const_align(ira->codegen, ira->new_irb.exec, value->source_node, &casted_value->value, out);
+}
+
 static bool ir_resolve_unsigned(IrAnalyze *ira, IrInstruction *value, ZigType *int_type, uint64_t *out) {
     if (type_is_invalid(value->value.type))
         return false;
@@ -12029,6 +12072,140 @@ static Buf *ir_resolve_str(IrAnalyze *ira, IrInstruction *value) {
     return result;
 }
 
+static ZigType *ir_resolve_lazy_fn_type(CodeGen *codegen, IrExecutable *exec, AstNode *source_node,
+        LazyValueFnType *lazy_fn_type)
+{
+    AstNode *proto_node = lazy_fn_type->proto_node;
+
+    FnTypeId fn_type_id = {0};
+    init_fn_type_id(&fn_type_id, proto_node, proto_node->data.fn_proto.params.length);
+
+    for (; fn_type_id.next_param_index < fn_type_id.param_count; fn_type_id.next_param_index += 1) {
+        AstNode *param_node = proto_node->data.fn_proto.params.at(fn_type_id.next_param_index);
+        assert(param_node->type == NodeTypeParamDecl);
+
+        bool param_is_var_args = param_node->data.param_decl.is_var_args;
+        if (param_is_var_args) {
+            if (fn_type_id.cc == CallingConventionC) {
+                fn_type_id.param_count = fn_type_id.next_param_index;
+                continue;
+            } else if (fn_type_id.cc == CallingConventionUnspecified) {
+                return get_generic_fn_type(codegen, &fn_type_id);
+            } else {
+                zig_unreachable();
+            }
+        }
+        FnTypeParamInfo *param_info = &fn_type_id.param_info[fn_type_id.next_param_index];
+        param_info->is_noalias = param_node->data.param_decl.is_noalias;
+
+        if (lazy_fn_type->param_types[fn_type_id.next_param_index] == nullptr) {
+            param_info->type = nullptr;
+            return get_generic_fn_type(codegen, &fn_type_id);
+        } else {
+            ZigType *param_type = ir_resolve_const_type(codegen, exec, source_node,
+                    lazy_fn_type->param_types[fn_type_id.next_param_index]);
+            if (type_is_invalid(param_type))
+                return nullptr;
+            switch (type_requires_comptime(codegen, param_type)) {
+            case ReqCompTimeYes:
+                if (!calling_convention_allows_zig_types(fn_type_id.cc)) {
+                    exec_add_error_node(codegen, exec, source_node,
+                        buf_sprintf("parameter of type '%s' not allowed in function with calling convention '%s'",
+                            buf_ptr(&param_type->name), calling_convention_name(fn_type_id.cc)));
+                    return nullptr;
+                }
+                param_info->type = param_type;
+                fn_type_id.next_param_index += 1;
+                return get_generic_fn_type(codegen, &fn_type_id);
+            case ReqCompTimeInvalid:
+                return nullptr;
+            case ReqCompTimeNo:
+                break;
+            }
+            if (!type_has_bits(param_type) && !calling_convention_allows_zig_types(fn_type_id.cc)) {
+                exec_add_error_node(codegen, exec, source_node,
+                    buf_sprintf("parameter of type '%s' has 0 bits; not allowed in function with calling convention '%s'",
+                        buf_ptr(&param_type->name), calling_convention_name(fn_type_id.cc)));
+                return nullptr;
+            }
+            param_info->type = param_type;
+        }
+
+    }
+
+    if (lazy_fn_type->align_val != nullptr) {
+        if (!ir_resolve_const_align(codegen, exec, source_node, lazy_fn_type->align_val, &fn_type_id.alignment))
+            return nullptr;
+    }
+
+    fn_type_id.return_type = ir_resolve_const_type(codegen, exec, source_node, lazy_fn_type->return_type);
+    if (type_is_invalid(fn_type_id.return_type))
+        return nullptr;
+    if (fn_type_id.return_type->id == ZigTypeIdOpaque) {
+        exec_add_error_node(codegen, exec, source_node,
+            buf_sprintf("return type cannot be opaque"));
+        return nullptr;
+    }
+
+    if (lazy_fn_type->async_allocator_type != nullptr) {
+        fn_type_id.async_allocator_type = ir_resolve_const_type(codegen, exec, source_node,
+                lazy_fn_type->async_allocator_type);
+        if (type_is_invalid(fn_type_id.async_allocator_type))
+            return nullptr;
+    }
+
+    return get_fn_type(codegen, &fn_type_id);
+}
+
+Error ir_resolve_lazy(CodeGen *codegen, AstNode *source_node, ConstExprValue *val) {
+    Error err;
+    if (val->special != ConstValSpecialLazy)
+        return ErrorNone;
+    IrExecutable *exec = val->data.x_lazy->exec;
+    switch (val->data.x_lazy->id) {
+        case LazyValueIdInvalid:
+            zig_unreachable();
+        case LazyValueIdAlignOf: {
+            LazyValueAlignOf *lazy_align_of = reinterpret_cast<LazyValueAlignOf *>(val->data.x_lazy);
+            if ((err = type_resolve(codegen, lazy_align_of->target_type, ResolveStatusAlignmentKnown)))
+                return err;
+            uint64_t align_in_bytes = get_abi_alignment(codegen, lazy_align_of->target_type);
+            val->special = ConstValSpecialStatic;
+            assert(val->type->id == ZigTypeIdComptimeInt);
+            bigint_init_unsigned(&val->data.x_bigint, align_in_bytes);
+            return ErrorNone;
+        }
+        case LazyValueIdSliceType: {
+            LazyValueSliceType *lazy_slice_type = reinterpret_cast<LazyValueSliceType *>(val->data.x_lazy);
+            uint32_t align_bytes = 0;
+            if (lazy_slice_type->align_val != nullptr) {
+                if (!ir_resolve_const_align(codegen, exec, source_node, lazy_slice_type->align_val, &align_bytes))
+                    return ErrorSemanticAnalyzeFail;
+            }
+            if ((err = type_resolve(codegen, lazy_slice_type->elem_type, ResolveStatusZeroBitsKnown)))
+                return err;
+            ZigType *slice_ptr_type = get_pointer_to_type_extra(codegen, lazy_slice_type->elem_type,
+                    lazy_slice_type->is_const, lazy_slice_type->is_volatile, PtrLenUnknown, align_bytes,
+                    0, 0, lazy_slice_type->is_allowzero);
+            val->special = ConstValSpecialStatic;
+            assert(val->type->id == ZigTypeIdMetaType);
+            val->data.x_type = get_slice_type(codegen, slice_ptr_type);
+            return ErrorNone;
+        }
+        case LazyValueIdFnType: {
+            ZigType *fn_type = ir_resolve_lazy_fn_type(codegen, exec, source_node,
+                    reinterpret_cast<LazyValueFnType *>(val->data.x_lazy));
+            if (fn_type == nullptr)
+                return ErrorSemanticAnalyzeFail;
+            val->special = ConstValSpecialStatic;
+            assert(val->type->id == ZigTypeIdMetaType);
+            val->data.x_type = fn_type;
+            return ErrorNone;
+        }
+    }
+    zig_unreachable();
+}
+
 static IrInstruction *ir_analyze_instruction_add_implicit_return_type(IrAnalyze *ira,
         IrInstructionAddImplicitReturnType *instruction)
 {
@@ -13964,20 +14141,19 @@ static bool ir_analyze_fn_call_generic_arg(IrAnalyze *ira, AstNode *fn_proto_nod
 }
 
 static ZigVar *get_fn_var_by_index(ZigFn *fn_entry, size_t index) {
+    FnTypeParamInfo *src_param_info = &fn_entry->type_entry->data.fn.fn_type_id.param_info[index];
+    if (!type_has_bits(src_param_info->type))
+        return nullptr;
+
     size_t next_var_i = 0;
-    FnGenParamInfo *gen_param_info = fn_entry->type_entry->data.fn.gen_param_info;
-    assert(gen_param_info != nullptr);
     for (size_t param_i = 0; param_i < index; param_i += 1) {
-        FnGenParamInfo *info = &gen_param_info[param_i];
-        if (info->gen_index == SIZE_MAX)
+        FnTypeParamInfo *src_param_info = &fn_entry->type_entry->data.fn.fn_type_id.param_info[param_i];
+        if (!type_has_bits(src_param_info->type)) {
             continue;
+        }
 
         next_var_i += 1;
     }
-    FnGenParamInfo *info = &gen_param_info[index];
-    if (info->gen_index == SIZE_MAX)
-        return nullptr;
-
     return fn_entry->variable_list.at(next_var_i);
 }
 
@@ -14003,7 +14179,7 @@ static IrInstruction *ir_get_var_ptr(IrAnalyze *ira, IrInstruction *instruction,
     if (linkage_makes_it_runtime)
         goto no_mem_slot;
 
-    if (var->const_value->special == ConstValSpecialStatic) {
+    if (value_is_comptime(var->const_value)) {
         mem_slot = var->const_value;
     } else {
         if (var->mem_slot_index != SIZE_MAX && (comptime_var_mem || var->gen_is_const)) {
@@ -14021,6 +14197,7 @@ static IrInstruction *ir_get_var_ptr(IrAnalyze *ira, IrInstruction *instruction,
             case ConstValSpecialRuntime:
                 goto no_mem_slot;
             case ConstValSpecialStatic: // fallthrough
+            case ConstValSpecialLazy: // fallthrough
             case ConstValSpecialUndef: {
                 ConstPtrMut ptr_mut;
                 if (comptime_var_mem) {
@@ -14301,7 +14478,7 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstructionCall *call
             AstNode *body_node = fn_entry->body_node;
             result = ir_eval_const_value(ira->codegen, exec_scope, body_node, return_type,
                 ira->new_irb.exec->backward_branch_count, ira->new_irb.exec->backward_branch_quota, fn_entry,
-                nullptr, call_instruction->base.source_node, nullptr, ira->new_irb.exec, return_type_node);
+                nullptr, call_instruction->base.source_node, nullptr, ira->new_irb.exec, return_type_node, false);
 
             if (inferred_err_set_type != nullptr) {
                 inferred_err_set_type->data.error_set.infer_fn = nullptr;
@@ -14497,7 +14674,8 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstructionCall *call
             ConstExprValue *align_result = ir_eval_const_value(ira->codegen, impl_fn->child_scope,
                     fn_proto_node->data.fn_proto.align_expr, get_align_amt_type(ira->codegen),
                     ira->new_irb.exec->backward_branch_count, ira->new_irb.exec->backward_branch_quota,
-                    nullptr, nullptr, fn_proto_node->data.fn_proto.align_expr, nullptr, ira->new_irb.exec, nullptr);
+                    nullptr, nullptr, fn_proto_node->data.fn_proto.align_expr, nullptr, ira->new_irb.exec, nullptr,
+                    false);
             IrInstructionConst *const_instruction = ir_create_instruction<IrInstructionConst>(&ira->new_irb,
                     impl_fn->child_scope, fn_proto_node->data.fn_proto.align_expr);
             const_instruction->base.value = *align_result;
@@ -15630,7 +15808,7 @@ static IrInstruction *ir_analyze_container_member_access_inner(IrAnalyze *ira,
         auto entry = container_scope->decl_table.maybe_get(field_name);
         Tld *tld = entry ? entry->value : nullptr;
         if (tld && tld->id == TldIdFn) {
-            resolve_top_level_decl(ira->codegen, tld, source_instr->source_node);
+            resolve_top_level_decl(ira->codegen, tld, source_instr->source_node, false);
             if (tld->resolution == TldResolutionInvalid)
                 return ira->codegen->invalid_instruction;
             TldFn *tld_fn = (TldFn *)tld;
@@ -15821,7 +15999,7 @@ static void add_link_lib_symbol(IrAnalyze *ira, Buf *lib_name, Buf *symbol_name,
 
 
 static IrInstruction *ir_analyze_decl_ref(IrAnalyze *ira, IrInstruction *source_instruction, Tld *tld) {
-    resolve_top_level_decl(ira->codegen, tld, source_instruction->source_node);
+    resolve_top_level_decl(ira->codegen, tld, source_instruction->source_node, false);
     if (tld->resolution == TldResolutionInvalid)
         return ira->codegen->invalid_instruction;
 
@@ -16477,22 +16655,29 @@ static IrInstruction *ir_analyze_instruction_set_float_mode(IrAnalyze *ira,
 static IrInstruction *ir_analyze_instruction_slice_type(IrAnalyze *ira,
         IrInstructionSliceType *slice_type_instruction)
 {
-    Error err;
-    uint32_t align_bytes = 0;
+    IrInstruction *result = ir_const(ira, &slice_type_instruction->base, ira->codegen->builtin_types.entry_type);
+    result->value.special = ConstValSpecialLazy;
+
+    LazyValueSliceType *lazy_slice_type = allocate<LazyValueSliceType>(1);
+    result->value.data.x_lazy = &lazy_slice_type->base;
+    lazy_slice_type->base.id = LazyValueIdSliceType;
+    lazy_slice_type->base.exec = ira->new_irb.exec;
+
     if (slice_type_instruction->align_value != nullptr) {
-        if (!ir_resolve_align(ira, slice_type_instruction->align_value->child, &align_bytes))
+        lazy_slice_type->align_val = ir_resolve_const(ira, slice_type_instruction->align_value->child, LazyOk);
+        if (lazy_slice_type->align_val == nullptr)
             return ira->codegen->invalid_instruction;
     }
 
-    ZigType *child_type = ir_resolve_type(ira, slice_type_instruction->child_type->child);
-    if (type_is_invalid(child_type))
+    lazy_slice_type->elem_type = ir_resolve_type(ira, slice_type_instruction->child_type->child);
+    if (type_is_invalid(lazy_slice_type->elem_type))
         return ira->codegen->invalid_instruction;
 
-    bool is_const = slice_type_instruction->is_const;
-    bool is_volatile = slice_type_instruction->is_volatile;
-    bool is_allow_zero = slice_type_instruction->is_allow_zero;
+    lazy_slice_type->is_const = slice_type_instruction->is_const;
+    lazy_slice_type->is_volatile = slice_type_instruction->is_volatile;
+    lazy_slice_type->is_allowzero = slice_type_instruction->is_allow_zero;
 
-    switch (child_type->id) {
+    switch (lazy_slice_type->elem_type->id) {
         case ZigTypeIdInvalid: // handled above
             zig_unreachable();
         case ZigTypeIdUnreachable:
@@ -16501,7 +16686,7 @@ static IrInstruction *ir_analyze_instruction_slice_type(IrAnalyze *ira,
         case ZigTypeIdArgTuple:
         case ZigTypeIdOpaque:
             ir_add_error_node(ira, slice_type_instruction->base.source_node,
-                    buf_sprintf("slice of type '%s' not allowed", buf_ptr(&child_type->name)));
+                    buf_sprintf("slice of type '%s' not allowed", buf_ptr(&lazy_slice_type->elem_type->name)));
             return ira->codegen->invalid_instruction;
         case ZigTypeIdMetaType:
         case ZigTypeIdVoid:
@@ -16523,14 +16708,7 @@ static IrInstruction *ir_analyze_instruction_slice_type(IrAnalyze *ira,
         case ZigTypeIdBoundFn:
         case ZigTypeIdPromise:
         case ZigTypeIdVector:
-            {
-                if ((err = type_resolve(ira->codegen, child_type, ResolveStatusZeroBitsKnown)))
-                    return ira->codegen->invalid_instruction;
-                ZigType *slice_ptr_type = get_pointer_to_type_extra(ira->codegen, child_type,
-                        is_const, is_volatile, PtrLenUnknown, align_bytes, 0, 0, is_allow_zero);
-                ZigType *result_type = get_slice_type(ira->codegen, slice_ptr_type);
-                return ir_const_type(ira, &slice_type_instruction->base, result_type);
-            }
+            return result;
     }
     zig_unreachable();
 }
@@ -16637,7 +16815,7 @@ static IrInstruction *ir_analyze_instruction_array_type(IrAnalyze *ira,
         case ZigTypeIdPromise:
         case ZigTypeIdVector:
             {
-                if ((err = ensure_complete_type(ira->codegen, child_type)))
+                if ((err = type_resolve(ira->codegen, child_type, ResolveStatusSizeKnown)))
                     return ira->codegen->invalid_instruction;
                 ZigType *result_type = get_array_type(ira->codegen, child_type, size);
                 return ir_const_type(ira, &array_type_instruction->base, result_type);
@@ -17513,6 +17691,8 @@ static IrInstruction *ir_analyze_container_init_fields(IrAnalyze *ira, IrInstruc
 static IrInstruction *ir_analyze_instruction_container_init_list(IrAnalyze *ira,
         IrInstructionContainerInitList *instruction)
 {
+    Error err;
+
     ZigType *container_type = ir_resolve_type(ira, instruction->container_type->child);
     if (type_is_invalid(container_type))
         return ira->codegen->invalid_instruction;
@@ -17541,6 +17721,10 @@ static IrInstruction *ir_analyze_instruction_container_init_list(IrAnalyze *ira,
             child_type = pointer_type->data.pointer.child_type;
         }
 
+        if ((err = type_resolve(ira->codegen, child_type, ResolveStatusSizeKnown))) {
+            return ira->codegen->invalid_instruction;
+        }
+
         ZigType *fixed_size_array_type = get_array_type(ira->codegen, child_type, elem_count);
 
         ConstExprValue const_val = {};
@@ -17923,10 +18107,11 @@ static ZigType *ir_type_info_get_type(IrAnalyze *ira, const char *type_name, Zig
     Error err;
     ConstExprValue *type_info_var = get_builtin_value(ira->codegen, "TypeInfo");
     assert(type_info_var->type->id == ZigTypeIdMetaType);
-    assertNoError(ensure_complete_type(ira->codegen, type_info_var->data.x_type));
-
     ZigType *type_info_type = type_info_var->data.x_type;
     assert(type_info_type->id == ZigTypeIdUnion);
+    if ((err = type_resolve(ira->codegen, type_info_type, ResolveStatusSizeKnown))) {
+        zig_unreachable();
+    }
 
     if (type_name == nullptr && root == nullptr)
         return type_info_type;
@@ -17960,7 +18145,7 @@ static Error ir_make_type_info_defs(IrAnalyze *ira, IrInstruction *source_instr,
 {
     Error err;
     ZigType *type_info_definition_type = ir_type_info_get_type(ira, "Definition", nullptr);
-    if ((err = ensure_complete_type(ira->codegen, type_info_definition_type)))
+    if ((err = type_resolve(ira->codegen, type_info_definition_type, ResolveStatusSizeKnown)))
         return err;
 
     ensure_field_index(type_info_definition_type, "name", 0);
@@ -17987,7 +18172,7 @@ static Error ir_make_type_info_defs(IrAnalyze *ira, IrInstruction *source_instr,
     while ((curr_entry = decl_it.next()) != nullptr) {
         // If the definition is unresolved, force it to be resolved again.
         if (curr_entry->value->resolution == TldResolutionUnresolved) {
-            resolve_top_level_decl(ira->codegen, curr_entry->value, curr_entry->value->source_node);
+            resolve_top_level_decl(ira->codegen, curr_entry->value, curr_entry->value->source_node, false);
             if (curr_entry->value->resolution != TldResolutionOk) {
                 return ErrorSemanticAnalyzeFail;
             }
@@ -18480,6 +18665,9 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInstruction *source_instr
                 ensure_field_index(result->type, "fields", 2);
 
                 ZigType *type_info_enum_field_type = ir_type_info_get_type(ira, "EnumField", nullptr);
+                if ((err = type_resolve(ira->codegen, type_info_enum_field_type, ResolveStatusSizeKnown))) {
+                    zig_unreachable();
+                }
                 uint32_t enum_field_count = type_entry->data.enumeration.src_field_count;
 
                 ConstExprValue *enum_field_array = create_const_vals(1);
@@ -18523,6 +18711,9 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInstruction *source_instr
                     result->data.x_optional = nullptr;
                     break;
                 }
+                if ((err = type_resolve(ira->codegen, type_info_error_type, ResolveStatusSizeKnown))) {
+                    zig_unreachable();
+                }
                 ConstExprValue *slice_val = create_const_vals(1);
                 result->data.x_optional = slice_val;
 
@@ -18619,6 +18810,8 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInstruction *source_instr
                 ensure_field_index(result->type, "fields", 2);
 
                 ZigType *type_info_union_field_type = ir_type_info_get_type(ira, "UnionField", nullptr);
+                if ((err = type_resolve(ira->codegen, type_info_union_field_type, ResolveStatusSizeKnown)))
+                    zig_unreachable();
                 uint32_t union_field_count = type_entry->data.unionation.src_field_count;
 
                 ConstExprValue *union_field_array = create_const_vals(1);
@@ -18696,6 +18889,9 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInstruction *source_instr
                 ensure_field_index(result->type, "fields", 1);
 
                 ZigType *type_info_struct_field_type = ir_type_info_get_type(ira, "StructField", nullptr);
+                if ((err = type_resolve(ira->codegen, type_info_struct_field_type, ResolveStatusSizeKnown))) {
+                    zig_unreachable();
+                }
                 uint32_t struct_field_count = type_entry->data.structure.src_field_count;
 
                 ConstExprValue *struct_field_array = create_const_vals(1);
@@ -18803,6 +18999,9 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInstruction *source_instr
                 }
                 // args: []TypeInfo.FnArg
                 ZigType *type_info_fn_arg_type = ir_type_info_get_type(ira, "FnArg", nullptr);
+                if ((err = type_resolve(ira->codegen, type_info_fn_arg_type, ResolveStatusSizeKnown))) {
+                    zig_unreachable();
+                }
                 size_t fn_arg_count = type_entry->data.fn.fn_type_id.param_count -
                         (is_varargs && type_entry->data.fn.fn_type_id.cc != CallingConventionC);
 
@@ -18962,7 +19161,7 @@ static IrInstruction *ir_analyze_instruction_c_import(IrAnalyze *ira, IrInstruct
     ZigType *void_type = ira->codegen->builtin_types.entry_void;
     ConstExprValue *cimport_result = ir_eval_const_value(ira->codegen, &cimport_scope->base, block_node, void_type,
         ira->new_irb.exec->backward_branch_count, ira->new_irb.exec->backward_branch_quota, nullptr,
-        &cimport_scope->buf, block_node, nullptr, nullptr, nullptr);
+        &cimport_scope->buf, block_node, nullptr, nullptr, nullptr, false);
     if (type_is_invalid(cimport_result->type))
         return ira->codegen->invalid_instruction;
 
@@ -20509,15 +20708,11 @@ static IrInstruction *ir_analyze_instruction_handle(IrAnalyze *ira, IrInstructio
 }
 
 static IrInstruction *ir_analyze_instruction_align_of(IrAnalyze *ira, IrInstructionAlignOf *instruction) {
-    Error err;
     IrInstruction *type_value = instruction->type_value->child;
     if (type_is_invalid(type_value->value.type))
         return ira->codegen->invalid_instruction;
     ZigType *type_entry = ir_resolve_type(ira, type_value);
 
-    if ((err = type_resolve(ira->codegen, type_entry, ResolveStatusAlignmentKnown)))
-        return ira->codegen->invalid_instruction;
-
     switch (type_entry->id) {
         case ZigTypeIdInvalid:
             zig_unreachable();
@@ -20549,12 +20744,25 @@ static IrInstruction *ir_analyze_instruction_align_of(IrAnalyze *ira, IrInstruct
         case ZigTypeIdUnion:
         case ZigTypeIdFn:
         case ZigTypeIdVector:
-            {
-                uint64_t align_in_bytes = get_abi_alignment(ira->codegen, type_entry);
-                return ir_const_unsigned(ira, &instruction->base, align_in_bytes);
-            }
+            break;
     }
-    zig_unreachable();
+    if (type_is_resolved(type_entry, ResolveStatusAlignmentKnown)) {
+        uint64_t align_in_bytes = get_abi_alignment(ira->codegen, type_entry);
+        return ir_const_unsigned(ira, &instruction->base, align_in_bytes);
+    }
+    // Here we create a lazy value in order to avoid resolving the alignment of the type
+    // immediately. This avoids false positive dependency loops such as:
+    // const Node = struct {
+    //     field: []align(@alignOf(Node)) Node,
+    // };
+    LazyValueAlignOf *lazy_align_of = allocate<LazyValueAlignOf>(1);
+    lazy_align_of->base.id = LazyValueIdAlignOf;
+    lazy_align_of->base.exec = ira->new_irb.exec;
+    lazy_align_of->target_type = type_entry;
+    IrInstruction *result = ir_const(ira, &instruction->base, ira->codegen->builtin_types.entry_num_lit_int);
+    result->value.special = ConstValSpecialLazy;
+    result->value.data.x_lazy = &lazy_align_of->base;
+    return result;
 }
 
 static IrInstruction *ir_analyze_instruction_overflow_op(IrAnalyze *ira, IrInstructionOverflowOp *instruction) {
@@ -20809,96 +21017,77 @@ static IrInstruction *ir_analyze_instruction_fn_proto(IrAnalyze *ira, IrInstruct
     AstNode *proto_node = instruction->base.source_node;
     assert(proto_node->type == NodeTypeFnProto);
 
+    IrInstruction *result = ir_const(ira, &instruction->base, ira->codegen->builtin_types.entry_type);
+    result->value.special = ConstValSpecialLazy;
+
+    LazyValueFnType *lazy_fn_type = allocate<LazyValueFnType>(1);
+    result->value.data.x_lazy = &lazy_fn_type->base;
+    lazy_fn_type->base.id = LazyValueIdFnType;
+    lazy_fn_type->base.exec = ira->new_irb.exec;
+
     if (proto_node->data.fn_proto.auto_err_set) {
         ir_add_error(ira, &instruction->base,
             buf_sprintf("inferring error set of return type valid only for function definitions"));
         return ira->codegen->invalid_instruction;
     }
 
-    FnTypeId fn_type_id = {0};
-    init_fn_type_id(&fn_type_id, proto_node, proto_node->data.fn_proto.params.length);
+    size_t param_count = proto_node->data.fn_proto.params.length;
+    lazy_fn_type->proto_node = proto_node;
+    lazy_fn_type->param_types = allocate<ConstExprValue *>(param_count);
 
-    for (; fn_type_id.next_param_index < fn_type_id.param_count; fn_type_id.next_param_index += 1) {
-        AstNode *param_node = proto_node->data.fn_proto.params.at(fn_type_id.next_param_index);
+    for (size_t i = 0; i < param_count; i += 1) {
+        AstNode *param_node = proto_node->data.fn_proto.params.at(i);
         assert(param_node->type == NodeTypeParamDecl);
 
         bool param_is_var_args = param_node->data.param_decl.is_var_args;
+        lazy_fn_type->is_var_args = true;
         if (param_is_var_args) {
-            if (fn_type_id.cc == CallingConventionC) {
-                fn_type_id.param_count = fn_type_id.next_param_index;
-                continue;
-            } else if (fn_type_id.cc == CallingConventionUnspecified) {
-                return ir_const_type(ira, &instruction->base, get_generic_fn_type(ira->codegen, &fn_type_id));
+            if (proto_node->data.fn_proto.cc == CallingConventionC) {
+                break;
+            } else if (proto_node->data.fn_proto.cc == CallingConventionUnspecified) {
+                lazy_fn_type->is_generic = true;
+                return result;
             } else {
                 zig_unreachable();
             }
         }
-        FnTypeParamInfo *param_info = &fn_type_id.param_info[fn_type_id.next_param_index];
-        param_info->is_noalias = param_node->data.param_decl.is_noalias;
 
-        if (instruction->param_types[fn_type_id.next_param_index] == nullptr) {
-            param_info->type = nullptr;
-            return ir_const_type(ira, &instruction->base, get_generic_fn_type(ira->codegen, &fn_type_id));
-        } else {
-            IrInstruction *param_type_value = instruction->param_types[fn_type_id.next_param_index]->child;
-            if (type_is_invalid(param_type_value->value.type))
-                return ira->codegen->invalid_instruction;
-            ZigType *param_type = ir_resolve_type(ira, param_type_value);
-            switch (type_requires_comptime(ira->codegen, param_type)) {
-            case ReqCompTimeYes:
-                if (!calling_convention_allows_zig_types(fn_type_id.cc)) {
-                    ir_add_error(ira, param_type_value,
-                        buf_sprintf("parameter of type '%s' not allowed in function with calling convention '%s'",
-                            buf_ptr(&param_type->name), calling_convention_name(fn_type_id.cc)));
-                    return ira->codegen->invalid_instruction;
-                }
-                param_info->type = param_type;
-                fn_type_id.next_param_index += 1;
-                return ir_const_type(ira, &instruction->base, get_generic_fn_type(ira->codegen, &fn_type_id));
-            case ReqCompTimeInvalid:
-                return ira->codegen->invalid_instruction;
-            case ReqCompTimeNo:
-                break;
-            }
-            if (!type_has_bits(param_type) && !calling_convention_allows_zig_types(fn_type_id.cc)) {
-                ir_add_error(ira, param_type_value,
-                    buf_sprintf("parameter of type '%s' has 0 bits; not allowed in function with calling convention '%s'",
-                        buf_ptr(&param_type->name), calling_convention_name(fn_type_id.cc)));
-                return ira->codegen->invalid_instruction;
-            }
-            param_info->type = param_type;
+        if (instruction->param_types[i] == nullptr) {
+            lazy_fn_type->is_generic = true;
+            return result;
         }
 
+        IrInstruction *param_type_value = instruction->param_types[i]->child;
+        if (type_is_invalid(param_type_value->value.type))
+            return ira->codegen->invalid_instruction;
+        ConstExprValue *param_type_val = ir_resolve_const(ira, param_type_value, LazyOk);
+        if (param_type_val == nullptr)
+            return ira->codegen->invalid_instruction;
+        lazy_fn_type->param_types[i] = param_type_val;
     }
 
     if (instruction->align_value != nullptr) {
-        if (!ir_resolve_align(ira, instruction->align_value->child, &fn_type_id.alignment))
+        lazy_fn_type->align_val = ir_resolve_const(ira, instruction->align_value->child, LazyOk);
+        if (lazy_fn_type->align_val == nullptr)
             return ira->codegen->invalid_instruction;
     }
 
-    IrInstruction *return_type_value = instruction->return_type->child;
-    fn_type_id.return_type = ir_resolve_type(ira, return_type_value);
-    if (type_is_invalid(fn_type_id.return_type))
-        return ira->codegen->invalid_instruction;
-    if (fn_type_id.return_type->id == ZigTypeIdOpaque) {
-        ir_add_error(ira, instruction->return_type,
-            buf_sprintf("return type cannot be opaque"));
+    lazy_fn_type->return_type = ir_resolve_const(ira, instruction->return_type->child, LazyOk);
+    if (lazy_fn_type->return_type == nullptr)
         return ira->codegen->invalid_instruction;
-    }
 
-    if (fn_type_id.cc == CallingConventionAsync) {
+    if (proto_node->data.fn_proto.cc == CallingConventionAsync) {
         if (instruction->async_allocator_type_value == nullptr) {
             ir_add_error(ira, &instruction->base,
                 buf_sprintf("async fn proto missing allocator type"));
             return ira->codegen->invalid_instruction;
         }
-        IrInstruction *async_allocator_type_value = instruction->async_allocator_type_value->child;
-        fn_type_id.async_allocator_type = ir_resolve_type(ira, async_allocator_type_value);
-        if (type_is_invalid(fn_type_id.async_allocator_type))
+        lazy_fn_type->async_allocator_type = ir_resolve_const(ira, instruction->async_allocator_type_value->child, LazyOk);
+        if (lazy_fn_type->async_allocator_type == nullptr)
             return ira->codegen->invalid_instruction;
     }
 
-    return ir_const_type(ira, &instruction->base, get_fn_type(ira->codegen, &fn_type_id));
+    return result;
 }
 
 static IrInstruction *ir_analyze_instruction_test_comptime(IrAnalyze *ira, IrInstructionTestComptime *instruction) {
@@ -21567,8 +21756,11 @@ static Error buf_read_value_bytes(IrAnalyze *ira, CodeGen *codegen, AstNode *sou
                     val->type->data.vector.len);
         case ZigTypeIdEnum:
             switch (val->type->data.enumeration.layout) {
-                case ContainerLayoutAuto:
-                    zig_panic("TODO buf_read_value_bytes enum auto");
+                case ContainerLayoutAuto: {
+                    opt_ir_add_error_node(ira, codegen, source_node,
+                        buf_sprintf("compiler bug: TODO: implement enum byte reinterpretation"));
+                    return ErrorSemanticAnalyzeFail;
+                }
                 case ContainerLayoutPacked:
                     zig_panic("TODO buf_read_value_bytes enum packed");
                 case ContainerLayoutExtern: {
@@ -21864,7 +22056,7 @@ static IrInstruction *ir_analyze_instruction_decl_ref(IrAnalyze *ira,
     Tld *tld = instruction->tld;
     LVal lval = instruction->lval;
 
-    resolve_top_level_decl(ira->codegen, tld, instruction->base.source_node);
+    resolve_top_level_decl(ira->codegen, tld, instruction->base.source_node, true);
     if (tld->resolution == TldResolutionInvalid)
         return ira->codegen->invalid_instruction;
 
diff --git a/src/ir.hpp b/src/ir.hpp
index 0b85ad2c55..bf65328f70 100644
--- a/src/ir.hpp
+++ b/src/ir.hpp
@@ -16,7 +16,8 @@ bool ir_gen_fn(CodeGen *g, ZigFn *fn_entry);
 ConstExprValue *ir_eval_const_value(CodeGen *codegen, Scope *scope, AstNode *node,
         ZigType *expected_type, size_t *backward_branch_count, size_t backward_branch_quota,
         ZigFn *fn_entry, Buf *c_import_buf, AstNode *source_node, Buf *exec_name,
-        IrExecutable *parent_exec, AstNode *expected_type_source_node);
+        IrExecutable *parent_exec, AstNode *expected_type_source_node, bool allow_lazy);
+Error ir_resolve_lazy(CodeGen *codegen, AstNode *source_node, ConstExprValue *val);
 
 ZigType *ir_analyze(CodeGen *g, IrExecutable *old_executable, IrExecutable *new_executable,
         ZigType *expected_type, AstNode *expected_type_source_node);