Comparing a union's field with null or undefined no longer crashes

tslang/lib/TypeScript/MLIRGenImpl.h

@@ -3619,10 +3619,10 @@ class MLIRGenImpl
             auto isConst = false;
             mlir::Attribute value;
             isConst = isConstValue(constVal);
-            if (isConst)
+            // null and undefined are const values too, but not literals a discriminant field can hold
+            auto constantOp = isConst ? constVal.getDefiningOp<mlir_ts::ConstantOp>() : mlir_ts::ConstantOp();
+            if (constantOp)
             {
-                auto constantOp = constVal.getDefiningOp<mlir_ts::ConstantOp>();
-                assert(constantOp);
                 auto valueAttr = constantOp.getValueAttr();
 
                 MLIRCodeLogic mcl(builder, compileOptions);
@@ -3633,6 +3633,11 @@ class MLIRGenImpl
                     if (auto tupleType = dyn_cast<mlir_ts::TupleType>(unionSubType))
                     {
                         auto fieldIndex = tupleType.getIndex(fieldNameAttr);
+                        if (fieldIndex < 0)
+                        {
+                            continue;
+                        }
+
                         auto fieldType = tupleType.getType(fieldIndex);
                         if (auto literalType = dyn_cast<mlir_ts::LiteralType>(fieldType))
                         {
@@ -3657,6 +3662,11 @@ class MLIRGenImpl
                         if (auto interfaceInfo = getInterfaceInfoByFullName(interfaceType.getName().getValue()))
                         {
                             auto fieldInfo = interfaceInfo->findField(fieldNameAttr);
+                            if (!fieldInfo)
+                            {
+                                continue;
+                            }
+
                             if (auto literalType = dyn_cast<mlir_ts::LiteralType>(fieldInfo->type))
                             {
                                 if (literalType.getValue() == valueAttr)

tslang/test/tester/CMakeLists.txt

@@ -528,6 +528,7 @@ tslang_add_test(NAME test-compile-00-safe-cast-typeof COMMAND test-runner "${PRO
 tslang_add_test(NAME test-compile-00-safe-cast-while COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_while.ts")
 tslang_add_test(NAME test-compile-01-safe-cast-while COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/01safe_cast_while.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-field-access COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_field_access.ts")
+tslang_add_test(NAME test-compile-00-safe-cast-null-field COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_null_field.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-bug COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_bug.ts")
 tslang_add_test(NAME test-compile-00-optional COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00optional.ts")
 tslang_add_test(NAME test-compile-01-optional COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/01optional.ts")
@@ -968,6 +969,7 @@ tslang_add_test(NAME test-jit-00-safe-cast-typeof COMMAND test-runner -jit "${PR
 tslang_add_test(NAME test-jit-00-safe-cast-while COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_while.ts")
 tslang_add_test(NAME test-jit-01-safe-cast-while COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/01safe_cast_while.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-field-access COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_field_access.ts")
+tslang_add_test(NAME test-jit-00-safe-cast-null-field COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_null_field.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-bug COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_bug.ts")
 tslang_add_test(NAME test-jit-00-optional COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00optional.ts")
 tslang_add_test(NAME test-jit-01-optional COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/01optional.ts")
@@ -1749,6 +1751,7 @@ set(TSLANG_CORPUS
     00reference_ref_deref.ts
     00safe_cast_bug.ts
     00safe_cast_field_access.ts
+    00safe_cast_null_field.ts
     00safe_cast_typeof.ts
     00safe_cast_while.ts
     00safe_cast.ts

tslang/test/tester/tests/00safe_cast_null_field.ts

@@ -0,0 +1,51 @@
+// A field of a union-typed object compared with null or undefined. The discriminated-union
+// narrowing took null and undefined for literal constants and crashed the compiler (#231).
+
+interface Circle {
+    kind: "circle";
+    r: number | null;
+}
+
+interface Square {
+    kind: "square";
+    r: number | null;
+}
+
+type Shape = Circle | Square;
+
+function hasR(s: Shape) {
+    if (s.r !== null) {
+        return true;
+    }
+
+    return false;
+}
+
+function hasRUndef(s: Shape) {
+    if (s.r === undefined) {
+        return false;
+    }
+
+    return true;
+}
+
+function kind(s: Shape) {
+    // a real literal must still narrow
+    if (s.kind === "circle") {
+        return 1;
+    }
+
+    return 2;
+}
+
+function main() {
+    const c: Circle = { kind: "circle", r: 1 };
+    const q: Square = { kind: "square", r: null };
+    assert(hasR(c));
+    assert(!hasR(q));
+    assert(hasRUndef(c));
+    assert(kind(c) == 1);
+    assert(kind(q) == 2);
+
+    print("done.");
+}