disallow '_' prong when switching on non-exhaustive tagged union

A tagged union cannot legally be initiated to an invalid enumeration

1 files changed, 11 insertions, 5 deletions

diff --git a/src/ir.cpp b/src/ir.cpp
index f56a0681df..347cae7e79 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -14138,7 +14138,7 @@ static IrInstGen *ir_analyze_union_to_tag(IrAnalyze *ira, IrInst* source_instr,
     // If there is only 1 possible tag, then we know at comptime what it is.
     if (wanted_type->data.enumeration.layout == ContainerLayoutAuto &&
         wanted_type->data.enumeration.src_field_count == 1 &&
-        !wanted_type->data.enumeration.non_exhaustive) // TODO are non-exhaustive union tag types supposed to be allowed?
+        !wanted_type->data.enumeration.non_exhaustive)
     {
         IrInstGen *result = ir_const(ira, source_instr, wanted_type);
         result->value->special = ConstValSpecialStatic;
@@ -23816,7 +23816,6 @@ static IrInstGen *ir_analyze_instruction_switch_target(IrAnalyze *ira,
                 bigint_init_bigint(&result->value->data.x_enum_tag, &pointee_val->data.x_union.tag);
                 return result;
             }
-            // TODO are non-exhaustive union tag types supposed to be allowed?
             if (tag_type->data.enumeration.src_field_count == 1 && !tag_type->data.enumeration.non_exhaustive) {
                 IrInstGen *result = ir_const(ira, &switch_target_instruction->base.base, tag_type);
                 TypeEnumField *only_field = &tag_type->data.enumeration.fields[0];
@@ -28839,6 +28838,10 @@ static IrInstGen *ir_analyze_instruction_check_switch_prongs(IrAnalyze *ira,
     if (type_is_invalid(switch_type))
         return ira->codegen->invalid_inst_gen;
 
+    ZigValue *original_value = ((IrInstSrcSwitchTarget *)(instruction->target_value))->target_value_ptr->child->value;
+    bool target_is_originally_union = original_value->type->id == ZigTypeIdPointer &&
+        original_value->type->data.pointer.child_type->id == ZigTypeIdUnion;
+
     if (switch_type->id == ZigTypeIdEnum) {
         HashMap<BigInt, AstNode *, bigint_hash, bigint_eql> field_prev_uses = {};
         field_prev_uses.init(switch_type->data.enumeration.src_field_count);
@@ -28894,9 +28897,12 @@ static IrInstGen *ir_analyze_instruction_check_switch_prongs(IrAnalyze *ira,
             }
         }
         if (instruction->have_underscore_prong) {
-            if (!switch_type->data.enumeration.non_exhaustive){
+            if (!switch_type->data.enumeration.non_exhaustive) {
+                ir_add_error(ira, &instruction->base.base,
+                    buf_sprintf("switch on exhaustive enum has `_` prong"));
+            } else if (target_is_originally_union) {
                 ir_add_error(ira, &instruction->base.base,
-                    buf_sprintf("switch on non-exhaustive enum has `_` prong"));
+                    buf_sprintf("`_` prong not allowed when switching on tagged union"));
             }
             for (uint32_t i = 0; i < switch_type->data.enumeration.src_field_count; i += 1) {
                 TypeEnumField *enum_field = &switch_type->data.enumeration.fields[i];
@@ -28911,7 +28917,7 @@ static IrInstGen *ir_analyze_instruction_check_switch_prongs(IrAnalyze *ira,
                 }
             }
         } else if (instruction->else_prong == nullptr) {
-            if (switch_type->data.enumeration.non_exhaustive) {
+            if (switch_type->data.enumeration.non_exhaustive && !target_is_originally_union) {
                 ir_add_error(ira, &instruction->base.base,
                     buf_sprintf("switch on non-exhaustive enum must include `else` or `_` prong"));
             }