autodoc: handle the changes to field init body instruction re-use

Author: kcbanner

src/Autodoc.zig

@@ -3702,6 +3702,11 @@ fn walkInstruction(
                         call_ctx,
                     );
 
+                    // Inside field init bodies, the struct decl instruction is used to refer to the
+                    // field type during the second pass of analysis.
+                    try self.repurposed_insts.put(self.arena, @intCast(inst_index), {});
+                    defer _ = self.repurposed_insts.remove(@intCast(inst_index));
+
                     var field_type_refs: std.ArrayListUnmanaged(DocData.Expr) = .{};
                     var field_default_refs: std.ArrayListUnmanaged(?DocData.Expr) = .{};
                     var field_name_indexes: std.ArrayListUnmanaged(usize) = .{};