A field of a union of same-layout object types is read from the base type (#384)

`s.kind` / `s.r` on `s: { kind: "circle", r: number } | { kind: "square", r:
number }` failed verification: "'ts.PropertyRef' op operand #0 must be ...
tuple reference type ... but got '!ts.ref<!ts.union<...>>'". Such a union
needs no tag and is stored as its base type, and property access switched to
that type (actualType = baseType), but the value it accessed stayed the union,
and MLIRPropertyAccessCodeLogic still held the original expression: the tuple
accessor read the field through the union's reference.

The value is now cast to the base type, and the access logic is given it
(MLIRPropertyAccessCodeLogic::setExpression). Found in the #231 review.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: ASDAlexander77

tslang/include/TypeScript/MLIRLogic/MLIRCodeLogic.h

@@ -1325,7 +1325,13 @@ class MLIRPropertyAccessCodeLogic
         {
             name = strAttr.getValue();
         }
-    }    
+    }
+
+    // the object is accessed as another value of it - a union as its base type
+    void setExpression(mlir::Value newExpression)
+    {
+        expression = newExpression;
+    }
 
     mlir::Value Enum(mlir_ts::EnumType enumType)
     {

tslang/lib/TypeScript/MLIRGenAccessCall.cpp

@@ -169,8 +169,14 @@ namespace mlirgen
             {
                 LLVM_DEBUG(llvm::dbgs() << "\n!! mlirGenPropertyAccessExpressionBaseLogic: union type " << baseType << "\n";);
                 actualType = baseType;
+                // The value is the base type as well: a union of object types sharing one layout
+                // (`{ kind: "a", r: number } | { kind: "b", r: number }`) is stored as it. Left a
+                // union, the field was read through the union's reference - a PropertyRef the
+                // verifier rejects.
+                objectValue = builder.create<mlir_ts::CastOp>(location, baseType, objectValue);
+                cl.setExpression(objectValue);
             }
-        }        
+        }
 
         // class member access
         auto classAccessWithObject = [&](mlir_ts::ClassType classType, mlir::Value objectValue) {

tslang/test/tester/CMakeLists.txt

@@ -532,6 +532,7 @@ tslang_add_test(NAME test-compile-00-safe-cast-while COMMAND test-runner "${PROJ
 tslang_add_test(NAME test-compile-01-safe-cast-while COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/01safe_cast_while.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-field-access COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_field_access.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-early-exit COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_early_exit.ts")
+tslang_add_test(NAME test-compile-00-union-object-types-access COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00union_object_types_access.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-null-field COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_null_field.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-else-scope COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_else_scope.ts")
 tslang_add_test(NAME test-compile-00-safe-cast-bug COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_bug.ts")
@@ -979,6 +980,7 @@ tslang_add_test(NAME test-jit-00-safe-cast-while COMMAND test-runner -jit "${PRO
 tslang_add_test(NAME test-jit-01-safe-cast-while COMMAND test-runner -jit "${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 "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_field_access.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-early-exit COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_early_exit.ts")
+tslang_add_test(NAME test-jit-00-union-object-types-access COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00union_object_types_access.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-null-field COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_null_field.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-else-scope COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_else_scope.ts")
 tslang_add_test(NAME test-jit-00-safe-cast-bug COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00safe_cast_bug.ts")
@@ -1767,6 +1769,7 @@ set(TSLANG_CORPUS
     00safe_cast_bug.ts
     00safe_cast_field_access.ts
     00safe_cast_early_exit.ts
+    00union_object_types_access.ts
     00safe_cast_null_field.ts
     00safe_cast_else_scope.ts
     00safe_cast_typeof.ts

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

@@ -0,0 +1,41 @@
+// A field of a union of object types that share one layout. The union is stored as its base type,
+// but the field was read through the union's reference - a 'ts.PropertyRef' the verifier rejected
+// (#231).
+
+type Shape = { kind: "circle", r: number } | { kind: "square", r: number };
+
+function kind(s: Shape) {
+    if (s.kind === "circle") {
+        return 1;
+    }
+
+    return 2;
+}
+
+function size(s: Shape) {
+    return s.r;
+}
+
+type Sized = { kind: "circle", r: number | null } | { kind: "square", r: number | null };
+
+function hasSize(s: Sized) {
+    if (s.r !== null) {
+        return true;
+    }
+
+    return false;
+}
+
+function main() {
+    const c: Shape = { kind: "circle", r: 1 };
+    const q: Shape = { kind: "square", r: 2 };
+    assert(kind(c) == 1 && kind(q) == 2);
+    assert(size(c) == 1 && size(q) == 2);
+
+    const c2: Sized = { kind: "circle", r: 3 };
+    const q2: Sized = { kind: "square", r: null };
+    assert(hasSize(c2));
+    assert(!hasSize(q2));
+
+    print("done.");
+}