union type check

.claude/rules.md

@@ -205,6 +205,7 @@ Existing bridges: `regex-bridge.c`, `yyjson-bridge.c`, `os-bridge.c`, `child-pro
 5. **Type cast field order must match FULL struct layout** — when the type extends a parent interface, the struct includes ALL parent fields. `as { name, closureInfo }` on a `LiftedFunction extends FunctionNode` (10 fields) reads index 1 instead of index 9. Include every field.
 6. **`ret void` not `unreachable`** at end of void functions
 7. **Class structs: boolean is `i1`; Interface structs: boolean is `double`**
+8. **Set feature flags when emitting gated extern calls** — runtime declarations for C bridges (yyjson, curl, etc.) are conditionally emitted behind flags like `usesJson`, `usesCurl`. Any code path that emits `call @csyyjson_*` must call `ctx.setUsesJson(true)`, etc. Missing this causes "undefined value" errors from `opt` because the `declare` is never emitted.
 
 ## Interface Field Iteration
 

src/codegen/expressions/access/index.ts

@@ -35,6 +35,7 @@ export interface IndexAccessGeneratorContext {
   isStringExpression(expr: Expression): boolean;
   readonly stringGen: IStringGenerator;
   ensureDouble(value: string): string;
+  setUsesJson(value: boolean): void;
 }
 
 /**
@@ -427,6 +428,7 @@ export class IndexAccessGenerator {
   }
 
   private generateJSONArrayIndex(expr: IndexAccessNode, params: string[]): string {
+    this.ctx.setUsesJson(true);
     // Load JSON array pointer
     const varName = (expr.object as VariableNode).name;
     const jsonPtrPtr = this.ctx.getVariableAlloca(varName)!;
@@ -514,6 +516,7 @@ export class IndexAccessGenerator {
   }
 
   private generateJSONMemberArrayIndex(expr: IndexAccessNode, params: string[]): string {
+    this.ctx.setUsesJson(true);
     const jsonPtr = this.ctx.generateExpression(expr.object, params);
 
     const ptrType = this.ctx.getVariableType(jsonPtr);

src/codegen/llvm-generator.ts

@@ -117,6 +117,8 @@ import type { TypeChecker } from "../typescript/type-checker.js";
 import { InterfaceStructGenerator } from "./types/interface-struct-generator.js";
 import { JsonObjectMeta } from "./expressions/access/member.js";
 import type { TargetInfo } from "../target-types.js";
+import { checkClosureMutations } from "../semantic/closure-mutation-checker.js";
+import { checkUnionTypes } from "../semantic/union-type-checker.js";
 
 export interface SemaSymbolData {
   names: string[];
@@ -2340,6 +2342,10 @@ export class LLVMGenerator extends BaseGenerator implements IGeneratorContext {
   }
 
   generateParts(): string[] {
+    // Run semantic checks before emitting any IR.
+    checkClosureMutations(this.ast);
+    checkUnionTypes(this.ast);
+
     const irParts: string[] = [];
 
     const interfaceStructDefs = this.interfaceStructGen.generateStructTypeDefinitions();