Sema: allow in-memory coercion of equivalent tuples

This is a workaround to the issue that tuple equality is currently
broken for explicit tuple types (created using `struct { .. }` syntax).
After the PTR changes in the previous commit, self-hosting was broken
without this change due to a tuple type being recreated in a peer
resolution.

This doesn't add any InMemoryCoercionResult field for this case, because
this is a temporary addition to the compiler which can be removed when
some bugs surrounding tuples are fixed.

src/Sema.zig

@@ -26594,6 +26594,23 @@ fn coerceInMemoryAllowed(
  return .ok;
  }
 
+ // Tuples
+ // TODO: this can go away once tuple type equality works
+ if (dest_ty.isTuple() and src_ty.isTuple()) tuple: {
+ if (dest_ty.containerLayout() != src_ty.containerLayout()) break :tuple;
+ if (dest_ty.structFieldCount() != src_ty.structFieldCount()) break :tuple;
+ const field_count = dest_ty.structFieldCount();
+ for (0..field_count) |field_idx| {
+ if (dest_ty.structFieldIsComptime(field_idx) != src_ty.structFieldIsComptime(field_idx)) break :tuple;
+ if (dest_ty.structFieldAlign(field_idx, target) != src_ty.structFieldAlign(field_idx, target)) break :tuple;
+ const dest_field_ty = dest_ty.structFieldType(field_idx);
+ const src_field_ty = src_ty.structFieldType(field_idx);
+ const field = try sema.coerceInMemoryAllowed(block, dest_field_ty, src_field_ty, dest_is_mut, target, dest_src, src_src);
+ if (field != .ok) break :tuple;
+ }
+ return .ok;
+ }
+
  return InMemoryCoercionResult{ .no_match = .{
  .actual = dest_ty,
  .wanted = src_ty,