fix(as): compiler crashed when duplicate inner function declared in function body

assemblyscript/src/compiler.ts

@@ -7820,6 +7820,18 @@ export class Compiler extends DiagnosticEmitter {
     let sourceFunction = flow.targetFunction;
     let isNamed = declaration.name.text.length > 0;
     let isSemanticallyAnonymous = !isNamed || contextualType != Type.void;
+
+    // Check for duplicate named function declarations before creating the
+    // prototype, since registering a concrete element with a duplicate
+    // internalName would trigger an assertion error.
+    if (!isSemanticallyAnonymous) {
+      let existingLocal = flow.getScopedLocal(declaration.name.text);
+      if (existingLocal) {
+        this.error(DiagnosticCode.Duplicate_identifier_0, declaration.name.range, declaration.name.text);
+        return this.module.unreachable();
+      }
+    }
+
     let closureInfo = this.program.closureScanner.getClosureFunctionInfo(declaration);
     let prototype = new FunctionPrototype(
       isSemanticallyAnonymous

tests/frontend/compiler/duplicate-function-in-scope.json

@@ -0,0 +1,3 @@
+{
+  "stderr": ["TS2300: Duplicate identifier 'inner'."]
+}

tests/frontend/compiler/duplicate-function-in-scope.ts

@@ -0,0 +1,14 @@
+// Duplicate named function declarations in the same scope should
+// produce a diagnostic instead of crashing the compiler.
+
+export function test(): void {
+  function inner(): i32 {
+    let x: i32 = 0;
+    return x;
+  }
+  function inner(): i32 {
+    let x: i32 = 0;
+    return x + 1;
+  }
+  inner();
+}