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Enable TypeForm support by default #11412

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0fee2d8
Enable TypeForm support by default
davidfstr Apr 30, 2026
b310584
Do not try to interpret a string as a TypeForm unless one is expected
davidfstr Apr 30, 2026
43adeea
Remove test-output.txt
davidfstr May 3, 2026
7233033
AI Coding: Ignore /plan directory
davidfstr May 3, 2026
7e27e4c
Prettier fixes #1
davidfstr May 3, 2026
b87b75f
Prettier fixes #2
davidfstr May 3, 2026
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1 change: 1 addition & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
Expand Up @@ -131,6 +131,7 @@ Thumbs.db
serena/
.beads/
AGENTS.md
/plan

# Generated benchmark output
packages/pyright-internal/src/tests/benchmarks/.generated/
Expand Down
109 changes: 44 additions & 65 deletions packages/pyright-internal/src/analyzer/typeEvaluator.ts
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@davidfstr davidfstr May 1, 2026

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Nit: Misspelling in commit message: "current interence context" -> "current inference context"

Original file line number Diff line number Diff line change
Expand Up @@ -1117,10 +1117,7 @@ export function createTypeEvaluator(

if (isAny(anySpecialForm)) {
TypeBase.setSpecialForm(anySpecialForm, anyClass);

if (isTypeFormSupported(node)) {
TypeBase.setTypeForm(anySpecialForm, convertToInstance(anySpecialForm));
}
TypeBase.setTypeForm(anySpecialForm, convertToInstance(anySpecialForm));
}
}
}
Expand Down Expand Up @@ -1314,7 +1311,7 @@ export function createTypeEvaluator(
expectingInstantiable = false;
}

typeResult = getTypeOfStringList(node, flags);
typeResult = getTypeOfStringList(node, flags, inferenceContext);
break;
}

Expand Down Expand Up @@ -1656,7 +1653,11 @@ export function createTypeEvaluator(
return typeResult;
}

function getTypeOfStringList(node: StringListNode, flags: EvalFlags): TypeResult {
function getTypeOfStringList(
node: StringListNode,
flags: EvalFlags,
inferenceContext?: InferenceContext
): TypeResult {
let typeResult: TypeResult | undefined;

if ((flags & EvalFlags.StrLiteralAsType) !== 0 && (flags & EvalFlags.TypeFormArg) === 0) {
Expand Down Expand Up @@ -1743,11 +1744,15 @@ export function createTypeEvaluator(
};
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@rchiodo rchiodo May 7, 2026

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Copilot generated:
The wantsTypeForm guard is well-designed — it prevents expensive string-as-TypeForm interpretation for plain string literals. However, [unverified] — it's unclear whether inferenceContext propagates deeply enough through container literal evaluation. For example, in d: dict[str, TypeForm] = {"key": "int"}, does the TypeForm expected type reach the string "int" via inference context? A targeted test case for container scenarios (list[TypeForm], dict[str, TypeForm]) would confirm or refute this.

[verified]

}

if (
node.d.strings.length !== 1 ||
node.d.strings[0].nodeType !== ParseNodeType.String ||
!isTypeFormSupported(node)
) {
// Only attempt to interpret the string as a TypeForm forward reference when
// there's a signal that a TypeForm value is wanted in this context. Doing it
// unconditionally can trigger expensive (and recursion-prone) type lookups
// for plain string literals in non-type contexts.
const wantsTypeForm =
(flags & EvalFlags.TypeFormArg) !== 0 ||
(inferenceContext !== undefined && expectedTypeWantsTypeForm(inferenceContext.expectedType));

if (node.d.strings.length !== 1 || node.d.strings[0].nodeType !== ParseNodeType.String || !wantsTypeForm) {
return typeResult;
}

Expand Down Expand Up @@ -5014,10 +5019,6 @@ export function createTypeEvaluator(
}

function addTypeFormForSymbol(node: ExpressionNode, type: Type, flags: EvalFlags, includesVarDecl: boolean): Type {
if (!isTypeFormSupported(node)) {
return type;
}

const isValid = isSymbolValidTypeExpression(type, includesVarDecl);

// If the type already has type information associated with it, don't replace.
Expand Down Expand Up @@ -7659,9 +7660,7 @@ export function createTypeEvaluator(
typeArgs: aliasTypeArgs,
});

if (isTypeFormSupported(node)) {
type = TypeBase.cloneWithTypeForm(type, reportedError ? undefined : convertToInstance(type));
}
type = TypeBase.cloneWithTypeForm(type, reportedError ? undefined : convertToInstance(type));

if (baseType.props?.typeAliasInfo) {
return { type, node };
Expand Down Expand Up @@ -8832,7 +8831,7 @@ export function createTypeEvaluator(
}

const typeFormResult = getTypeOfArgExpectingType(convertNodeToArg(node.d.args[0]), {
typeFormArg: isTypeFormSupported(node),
typeFormArg: true,
noNonTypeSpecialForms: true,
typeExpression: true,
});
Expand Down Expand Up @@ -13852,9 +13851,7 @@ export function createTypeEvaluator(
? prefetched.noneTypeClass
: convertToInstance(prefetched.noneTypeClass);

if (isTypeFormSupported(node)) {
type = TypeBase.cloneWithTypeForm(type, convertToInstance(type));
}
type = TypeBase.cloneWithTypeForm(type, convertToInstance(type));
}
} else if (
node.d.constType === KeywordType.True ||
Expand Down Expand Up @@ -15738,7 +15735,7 @@ export function createTypeEvaluator(
FunctionType.addParamSpecVariadics(functionType, convertToInstance(paramSpec));
}

if (isTypeFormSupported(errorNode) && isValidTypeForm) {
if (isValidTypeForm) {
functionType = TypeBase.cloneWithTypeForm(functionType, convertToInstance(functionType));
}

Expand Down Expand Up @@ -15954,7 +15951,7 @@ export function createTypeEvaluator(
result = TypeBase.cloneAsSpecialForm(result, ClassType.cloneAsInstance(prefetched.unionTypeClass));
}

if (isTypeFormSupported(node) && isValidTypeForm) {
if (isValidTypeForm) {
result = TypeBase.cloneWithTypeForm(result, convertToInstance(result));
}

Expand Down Expand Up @@ -16025,9 +16022,7 @@ export function createTypeEvaluator(
});
let resultType = ClassType.specialize(classType, convertedTypeArgs);

if (isTypeFormSupported(errorNode)) {
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));
}
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));

return resultType;
}
Expand Down Expand Up @@ -16059,9 +16054,7 @@ export function createTypeEvaluator(

let resultType = ClassType.specialize(classType, convertedTypeArgs);

if (isTypeFormSupported(errorNode)) {
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));
}
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));

return resultType;
}
Expand Down Expand Up @@ -16664,7 +16657,7 @@ export function createTypeEvaluator(
if (unionType.props?.typeForm) {
unionType = TypeBase.cloneWithTypeForm(unionType, undefined);
}
} else if (isTypeFormSupported(errorNode)) {
} else {
const typeFormType = combineTypes(types.map((t) => t.props!.typeForm!));
unionType = TypeBase.cloneWithTypeForm(unionType, typeFormType);
}
Expand Down Expand Up @@ -17025,9 +17018,7 @@ export function createTypeEvaluator(
specialType.shared.baseClasses.push(prefetched?.strClass ?? AnyType.create());
computeMroLinearization(specialType);

if (isTypeFormSupported(node)) {
specialType = TypeBase.cloneWithTypeForm(specialType, convertToInstance(specialType));
}
specialType = TypeBase.cloneWithTypeForm(specialType, convertToInstance(specialType));
}

// Handle 'Never' and 'NoReturn' specially.
Expand All @@ -17037,9 +17028,7 @@ export function createTypeEvaluator(
specialType
);

if (isTypeFormSupported(node)) {
specialType = TypeBase.cloneWithTypeForm(specialType, convertToInstance(specialType));
}
specialType = TypeBase.cloneWithTypeForm(specialType, convertToInstance(specialType));
}

writeTypeCache(node, { type: specialType }, EvalFlags.None);
Expand Down Expand Up @@ -21244,9 +21233,7 @@ export function createTypeEvaluator(

let resultType = aliasedName === 'Never' ? NeverType.createNever() : NeverType.createNoReturn();
resultType = TypeBase.cloneAsSpecialForm(resultType, classType);
if (isTypeFormSupported(errorNode)) {
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));
}
resultType = TypeBase.cloneWithTypeForm(resultType, convertToInstance(resultType));

return { type: resultType };
}
Expand All @@ -21268,9 +21255,7 @@ export function createTypeEvaluator(
typeType = explodeGenericClass(typeType);
}

if (isTypeFormSupported(errorNode)) {
typeType = TypeBase.cloneWithTypeForm(typeType, convertToInstance(typeType));
}
typeType = TypeBase.cloneWithTypeForm(typeType, convertToInstance(typeType));

return { type: typeType };
}
Expand Down Expand Up @@ -21430,9 +21415,7 @@ export function createTypeEvaluator(
typeType = explodeGenericClass(typeType);
}

if (isTypeFormSupported(errorNode)) {
typeType = TypeBase.cloneWithTypeForm(typeType, convertToInstance(typeType));
}
typeType = TypeBase.cloneWithTypeForm(typeType, convertToInstance(typeType));

return { type: typeType };
}
Expand All @@ -21449,12 +21432,7 @@ export function createTypeEvaluator(
/* isSpecialForm */ false
);

if (isTypeFormSupported(errorNode)) {
specializedClass = TypeBase.cloneWithTypeForm(
specializedClass,
convertToInstance(specializedClass)
);
}
specializedClass = TypeBase.cloneWithTypeForm(specializedClass, convertToInstance(specializedClass));

return { type: specializedClass };
}
Expand Down Expand Up @@ -21715,12 +21693,10 @@ export function createTypeEvaluator(

let specializedClass = ClassType.specialize(classType, typeArgTypes, typeArgs !== undefined);

if (isTypeFormSupported(errorNode)) {
specializedClass = TypeBase.cloneWithTypeForm(
specializedClass,
isValidTypeForm ? convertToInstance(specializedClass) : undefined
);
}
specializedClass = TypeBase.cloneWithTypeForm(
specializedClass,
isValidTypeForm ? convertToInstance(specializedClass) : undefined
);

return { type: specializedClass };
}
Expand Down Expand Up @@ -25598,6 +25574,16 @@ export function createTypeEvaluator(
return isAssignable;
}

function expectedTypeWantsTypeForm(expectedType: Type): boolean {
let result = false;
doForEachSubtype(expectedType, (subtype) => {
if (isClassInstance(subtype) && ClassType.isBuiltIn(subtype, 'TypeForm')) {
result = true;
}
});
return result;
}

// If the expected type is an explicit TypeForm type, see if the source
// type has an implicit TypeForm type that can be assigned to it. If so,
// convert to an explicit TypeForm type.
Expand Down Expand Up @@ -28701,13 +28687,6 @@ export function createTypeEvaluator(
return { sourceType: simpleSrcType, destType: simpleDestType };
}

function isTypeFormSupported(node: ParseNode) {
Comment thread
rchiodo marked this conversation as resolved.
const fileInfo = AnalyzerNodeInfo.getFileInfo(node);

// For now, enable only if enableExperimentalFeatures is true.
return fileInfo.diagnosticRuleSet.enableExperimentalFeatures;
}

function printType(type: Type, options?: PrintTypeOptions): string {
let flags = evaluatorOptions.printTypeFlags;

Expand Down