compiler: remove anonymous struct types, unify all tuples

This commit reworks how anonymous struct literals and tuples work.

Previously, an untyped anonymous struct literal
(e.g. `const x = .{ .a = 123 }`) was given an "anonymous struct type",
which is a special kind of struct which coerces using structural
equivalence. This mechanism was a holdover from before we used
RLS / result types as the primary mechanism of type inference. This
commit changes the language so that the type assigned here is a "normal"
struct type. It uses a form of equivalence based on the AST node and the
type's structure, much like a reified (`@Type`) type.

Additionally, tuples have been simplified. The distinction between
"simple" and "complex" tuple types is eliminated. All tuples, even those
explicitly declared using `struct { ... }` syntax, use structural
equivalence, and do not undergo staged type resolution. Tuples are very
restricted: they cannot have non-`auto` layouts, cannot have aligned
fields, and cannot have default values with the exception of `comptime`
fields. Tuples currently do not have optimized layout, but this can be
changed in the future.

This change simplifies the language, and fixes some problematic
coercions through pointers which led to unintuitive behavior.

Resolves: #16865

1 files changed, 7 insertions, 15 deletions

diff --git a/src/Zcu/PerThread.zig b/src/Zcu/PerThread.zig
index db1ee319dc..29b9716152 100644
--- a/src/Zcu/PerThread.zig
+++ b/src/Zcu/PerThread.zig
@@ -985,7 +985,6 @@ fn createFileRootStruct(
         .fields_len = fields_len,
         .known_non_opv = small.known_non_opv,
         .requires_comptime = if (small.known_comptime_only) .yes else .unknown,
-        .is_tuple = small.is_tuple,
         .any_comptime_fields = small.any_comptime_fields,
         .any_default_inits = small.any_default_inits,
         .inits_resolved = false,
@@ -3191,7 +3190,7 @@ pub fn ensureTypeUpToDate(pt: Zcu.PerThread, ty: InternPool.Index, already_updat
         .struct_type => |key| {
             const struct_obj = ip.loadStructType(ty);
             const outdated = already_updating or o: {
-                const anal_unit = AnalUnit.wrap(.{ .cau = struct_obj.cau.unwrap().? });
+                const anal_unit = AnalUnit.wrap(.{ .cau = struct_obj.cau });
                 const o = zcu.outdated.swapRemove(anal_unit) or
                     zcu.potentially_outdated.swapRemove(anal_unit);
                 if (o) {
@@ -3252,7 +3251,6 @@ fn recreateStructType(
 
     const key = switch (full_key) {
         .reified => unreachable, // never outdated
-        .empty_struct => unreachable, // never outdated
         .generated_tag => unreachable, // not a struct
         .declared => |d| d,
     };
@@ -3283,16 +3281,13 @@ fn recreateStructType(
     if (captures_len != key.captures.owned.len) return error.AnalysisFail;
 
     // The old type will be unused, so drop its dependency information.
-    ip.removeDependenciesForDepender(gpa, AnalUnit.wrap(.{ .cau = struct_obj.cau.unwrap().? }));
-
-    const namespace_index = struct_obj.namespace.unwrap().?;
+    ip.removeDependenciesForDepender(gpa, AnalUnit.wrap(.{ .cau = struct_obj.cau }));
 
     const wip_ty = switch (try ip.getStructType(gpa, pt.tid, .{
         .layout = small.layout,
         .fields_len = fields_len,
         .known_non_opv = small.known_non_opv,
         .requires_comptime = if (small.known_comptime_only) .yes else .unknown,
-        .is_tuple = small.is_tuple,
         .any_comptime_fields = small.any_comptime_fields,
         .any_default_inits = small.any_default_inits,
         .inits_resolved = false,
@@ -3308,17 +3303,17 @@ fn recreateStructType(
     errdefer wip_ty.cancel(ip, pt.tid);
 
     wip_ty.setName(ip, struct_obj.name);
-    const new_cau_index = try ip.createTypeCau(gpa, pt.tid, key.zir_index, namespace_index, wip_ty.index);
+    const new_cau_index = try ip.createTypeCau(gpa, pt.tid, key.zir_index, struct_obj.namespace, wip_ty.index);
     try ip.addDependency(
         gpa,
         AnalUnit.wrap(.{ .cau = new_cau_index }),
         .{ .src_hash = key.zir_index },
     );
-    zcu.namespacePtr(namespace_index).owner_type = wip_ty.index;
+    zcu.namespacePtr(struct_obj.namespace).owner_type = wip_ty.index;
     // No need to re-scan the namespace -- `zirStructDecl` will ultimately do that if the type is still alive.
     try zcu.comp.queueJob(.{ .resolve_type_fully = wip_ty.index });
 
-    const new_ty = wip_ty.finish(ip, new_cau_index.toOptional(), namespace_index);
+    const new_ty = wip_ty.finish(ip, new_cau_index.toOptional(), struct_obj.namespace);
     if (inst_info.inst == .main_struct_inst) {
         // This is the root type of a file! Update the reference.
         zcu.setFileRootType(inst_info.file, new_ty);
@@ -3337,7 +3332,6 @@ fn recreateUnionType(
 
     const key = switch (full_key) {
         .reified => unreachable, // never outdated
-        .empty_struct => unreachable, // never outdated
         .generated_tag => unreachable, // not a union
         .declared => |d| d,
     };
@@ -3429,9 +3423,7 @@ fn recreateEnumType(
     const ip = &zcu.intern_pool;
 
     const key = switch (full_key) {
-        .reified => unreachable, // never outdated
-        .empty_struct => unreachable, // never outdated
-        .generated_tag => unreachable, // never outdated
+        .reified, .generated_tag => unreachable, // never outdated
         .declared => |d| d,
     };
 
@@ -3575,7 +3567,7 @@ pub fn ensureNamespaceUpToDate(pt: Zcu.PerThread, namespace_index: Zcu.Namespace
     };
 
     const key = switch (full_key) {
-        .reified, .empty_struct, .generated_tag => {
+        .reified, .generated_tag => {
             // Namespace always empty, so up-to-date.
             namespace.generation = zcu.generation;
             return;