incremental: correctly return `error.AnalysisFail` when type structure changes

`Zcu.PerThead.ensureTypeUpToDate` is set up in such a way that it only
returns the updated type the first time it is called. In general, that's
okay; however, the exception is that we want the function to continue
returning `error.AnalysisFail` when the type has been lost, or its
number of captures changed.

Therefore, the check for this case now happens before the up-to-date
success return.

For simplicity, the number of captures is now handled by intentionally
losing the instruction in `Zcu.mapOldZirToNew`, since there is nothing
to gain from tracking a type when old instances of it can never be
reused.

1 files changed, 11 insertions, 9 deletions

diff --git a/src/InternPool.zig b/src/InternPool.zig
index fdeddcfa2f..c0b4d2f446 100644
--- a/src/InternPool.zig
+++ b/src/InternPool.zig
@@ -2029,15 +2029,7 @@ pub const Key = union(enum) {
     pub const NamespaceType = union(enum) {
         /// This type corresponds to an actual source declaration, e.g. `struct { ... }`.
         /// It is hashed based on its ZIR instruction index and set of captures.
-        declared: struct {
-            /// A `struct_decl`, `union_decl`, `enum_decl`, or `opaque_decl` instruction.
-            zir_index: TrackedInst.Index,
-            /// The captured values of this type. These values must be fully resolved per the language spec.
-            captures: union(enum) {
-                owned: CaptureValue.Slice,
-                external: []const CaptureValue,
-            },
-        },
+        declared: Declared,
         /// This type is an automatically-generated enum tag type for a union.
         /// It is hashed based on the index of the union type it corresponds to.
         generated_tag: struct {
@@ -2053,6 +2045,16 @@ pub const Key = union(enum) {
             /// A hash of this type's attributes, fields, etc, generated by Sema.
             type_hash: u64,
         },
+
+        pub const Declared = struct {
+            /// A `struct_decl`, `union_decl`, `enum_decl`, or `opaque_decl` instruction.
+            zir_index: TrackedInst.Index,
+            /// The captured values of this type. These values must be fully resolved per the language spec.
+            captures: union(enum) {
+                owned: CaptureValue.Slice,
+                external: []const CaptureValue,
+            },
+        };
     };
 
     pub const FuncType = struct {