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Defer checking of class static blocks #59607

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Defer checking of class static blocks
Andarist Aug 12, 2024
161d563
Merge remote-tracking branch 'origin/main' into defer-class-static-bl…
Andarist Jul 1, 2025
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7 changes: 5 additions & 2 deletions src/compiler/checker.ts
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Expand Up @@ -41494,7 +41494,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
}

function checkClassStaticBlockDeclaration(node: ClassStaticBlockDeclaration) {
function checkClassStaticBlockDeclarationDeferred(node: ClassStaticBlockDeclaration) {
checkGrammarModifiers(node);

forEachChild(node, checkSourceElement);
Expand Down Expand Up @@ -47937,7 +47937,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
case SyntaxKind.MethodSignature:
return checkMethodDeclaration(node as MethodDeclaration | MethodSignature);
case SyntaxKind.ClassStaticBlockDeclaration:
return checkClassStaticBlockDeclaration(node as ClassStaticBlockDeclaration);
return checkNodeDeferred(node);
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@jakebailey jakebailey Jun 30, 2025

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Maybe a stupid question, but why is it that this matters here, yet MethodSignatures are not deferred?

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@jakebailey jakebailey Jun 30, 2025

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As in, can't we write that same local type declaration in a method and it breaks? Or is that fine because the body gets deferred?

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@Andarist Andarist Jul 3, 2025

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My understanding is that:

  1. The same local type declaration in a method shouldn't suppress the error either.
  2. Object literal methods are deferred but class methods are not. If I try to defer class methods... a ton of tests break. So there has to be a reason behind why they are not deferred. Perhaps it's important for the variance worker?
  3. Class static blocks conceptually execute after the class declaration and they shouldn't affect the variance measurement and shouldn't trigger circularities in a way class methods/properties can. So it should be OK to defer them. They should behave in an almost same way as statements executed after the class. They only get a special treatment when it comes to class type parameters and this. But it feels like it shouldn't break anything if those get simply resolved in a deferred manner - after the class declaration gets processed.
  4. Right now it looks like this PR doesn't do anything because a bug has been introduced in the meantime: Missing constraint error in instantiation expression for a nested class #61982

case SyntaxKind.Constructor:
return checkConstructorDeclaration(node as ConstructorDeclaration);
case SyntaxKind.GetAccessor:
Expand Down Expand Up @@ -48248,6 +48248,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
case SyntaxKind.MethodSignature:
checkFunctionExpressionOrObjectLiteralMethodDeferred(node as FunctionExpression);
break;
case SyntaxKind.ClassStaticBlockDeclaration:
checkClassStaticBlockDeclarationDeferred(node as ClassStaticBlockDeclaration);
break;
case SyntaxKind.GetAccessor:
case SyntaxKind.SetAccessor:
checkAccessorDeclaration(node as AccessorDeclaration);
Expand Down
41 changes: 41 additions & 0 deletions tests/baselines/reference/classStaticBlockDoNotSpoilVariance1.errors.txt
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@@ -0,0 +1,41 @@
classStaticBlockDoNotSpoilVariance1.ts(7,35): error TS2344: Type 'A<T>' does not satisfy the constraint 'A<number>'.
Type 'T' is not assignable to type 'number'.
classStaticBlockDoNotSpoilVariance1.ts(20,36): error TS2344: Type 'A2<T>' does not satisfy the constraint 'A2<number>'.
Type 'T' is not assignable to type 'number'.


==== classStaticBlockDoNotSpoilVariance1.ts (2 errors) ====
class A<T = number> {
static {
type _<T extends A = A> = T;
}

value!: T;
child!: InstanceType<typeof A.B<A<T>>>;
~~~~
!!! error TS2344: Type 'A<T>' does not satisfy the constraint 'A<number>'.
!!! error TS2344: Type 'T' is not assignable to type 'number'.
!!! related TS2208 classStaticBlockDoNotSpoilVariance1.ts:1:9: This type parameter might need an `extends number` constraint.

static B = class B<T extends A = A> {
parent!: T;
};
}

const A2 = class A2<T = number> {
static {
type _<T extends A2 = A2> = T;
}

value!: T;
child!: InstanceType<typeof A2.B<A2<T>>>;
~~~~~
!!! error TS2344: Type 'A2<T>' does not satisfy the constraint 'A2<number>'.
!!! error TS2344: Type 'T' is not assignable to type 'number'.
!!! related TS2208 classStaticBlockDoNotSpoilVariance1.ts:14:21: This type parameter might need an `extends number` constraint.

static B = class B<T extends A2 = A2> {
parent!: T;
};
};

84 changes: 84 additions & 0 deletions tests/baselines/reference/classStaticBlockDoNotSpoilVariance1.symbols
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//// [tests/cases/conformance/classes/classStaticBlock/classStaticBlockDoNotSpoilVariance1.ts] ////

=== classStaticBlockDoNotSpoilVariance1.ts ===
class A<T = number> {
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 8))

static {
type _<T extends A = A> = T;
>_ : Symbol(_, Decl(classStaticBlockDoNotSpoilVariance1.ts, 1, 10))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 2, 11))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 2, 11))
}

value!: T;
>value : Symbol(A.value, Decl(classStaticBlockDoNotSpoilVariance1.ts, 3, 3))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 8))

child!: InstanceType<typeof A.B<A<T>>>;
>child : Symbol(A.child, Decl(classStaticBlockDoNotSpoilVariance1.ts, 5, 12))
>InstanceType : Symbol(InstanceType, Decl(lib.es5.d.ts, --, --))
>A.B : Symbol(A.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 6, 41))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>B : Symbol(A.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 6, 41))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 8))

static B = class B<T extends A = A> {
>B : Symbol(A.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 6, 41))
>B : Symbol(B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 8, 12))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 8, 21))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))
>A : Symbol(A, Decl(classStaticBlockDoNotSpoilVariance1.ts, 0, 0))

parent!: T;
>parent : Symbol(B.parent, Decl(classStaticBlockDoNotSpoilVariance1.ts, 8, 39))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 8, 21))

};
}

const A2 = class A2<T = number> {
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 5))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 20))

static {
type _<T extends A2 = A2> = T;
>_ : Symbol(_, Decl(classStaticBlockDoNotSpoilVariance1.ts, 14, 10))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 15, 11))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 15, 11))
}

value!: T;
>value : Symbol(A2.value, Decl(classStaticBlockDoNotSpoilVariance1.ts, 16, 3))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 20))

child!: InstanceType<typeof A2.B<A2<T>>>;
>child : Symbol(A2.child, Decl(classStaticBlockDoNotSpoilVariance1.ts, 18, 12))
>InstanceType : Symbol(InstanceType, Decl(lib.es5.d.ts, --, --))
>A2.B : Symbol(A2.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 19, 43))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>B : Symbol(A2.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 19, 43))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 20))

static B = class B<T extends A2 = A2> {
>B : Symbol(A2.B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 19, 43))
>B : Symbol(B, Decl(classStaticBlockDoNotSpoilVariance1.ts, 21, 12))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 21, 21))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))
>A2 : Symbol(A2, Decl(classStaticBlockDoNotSpoilVariance1.ts, 13, 10))

parent!: T;
>parent : Symbol(B.parent, Decl(classStaticBlockDoNotSpoilVariance1.ts, 21, 41))
>T : Symbol(T, Decl(classStaticBlockDoNotSpoilVariance1.ts, 21, 21))

};
};

85 changes: 85 additions & 0 deletions tests/baselines/reference/classStaticBlockDoNotSpoilVariance1.types
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//// [tests/cases/conformance/classes/classStaticBlock/classStaticBlockDoNotSpoilVariance1.ts] ////

=== classStaticBlockDoNotSpoilVariance1.ts ===
class A<T = number> {
>A : A<T>
> : ^^^^

static {
type _<T extends A = A> = T;
>_ : T
> : ^
}

value!: T;
>value : T
> : ^

child!: InstanceType<typeof A.B<A<T>>>;
>child : B<A<T>>
> : ^^^^^^^
>A.B : typeof B
> : ^^^^^^^^
>A : typeof A
> : ^^^^^^^^
>B : typeof B
> : ^^^^^^^^

static B = class B<T extends A = A> {
>B : typeof B
> : ^^^^^^^^
>class B<T extends A = A> { parent!: T; } : typeof B
> : ^^^^^^^^
>B : typeof B
> : ^^^^^^^^

parent!: T;
>parent : T
> : ^

};
}

const A2 = class A2<T = number> {
>A2 : typeof A2
> : ^^^^^^^^^
>class A2<T = number> { static { type _<T extends A2 = A2> = T; } value!: T; child!: InstanceType<typeof A2.B<A2<T>>>; static B = class B<T extends A2 = A2> { parent!: T; };} : typeof A2
> : ^^^^^^^^^
>A2 : typeof A2
> : ^^^^^^^^^

static {
type _<T extends A2 = A2> = T;
>_ : T
> : ^
}

value!: T;
>value : T
> : ^

child!: InstanceType<typeof A2.B<A2<T>>>;
>child : B<A2<T>>
> : ^^^^^^^^
>A2.B : typeof B
> : ^^^^^^^^
>A2 : typeof A2
> : ^^^^^^^^^
>B : typeof B
> : ^^^^^^^^

static B = class B<T extends A2 = A2> {
>B : typeof B
> : ^^^^^^^^
>class B<T extends A2 = A2> { parent!: T; } : typeof B
> : ^^^^^^^^
>B : typeof B
> : ^^^^^^^^

parent!: T;
>parent : T
> : ^

};
};

29 changes: 29 additions & 0 deletions tests/cases/conformance/classes/classStaticBlock/classStaticBlockDoNotSpoilVariance1.ts
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// @strict: true
// @target: esnext
// @noEmit: true

class A<T = number> {
static {
type _<T extends A = A> = T;
}

value!: T;
child!: InstanceType<typeof A.B<A<T>>>;

static B = class B<T extends A = A> {
parent!: T;
};
}

const A2 = class A2<T = number> {
static {
type _<T extends A2 = A2> = T;
}

value!: T;
child!: InstanceType<typeof A2.B<A2<T>>>;

static B = class B<T extends A2 = A2> {
parent!: T;
};
};
19 changes: 19 additions & 0 deletions tests/cases/fourslash/quickInfoAvoidsClassVarianceCircularity1.ts
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@Andarist Andarist Aug 12, 2024

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this one was already fixed by #53549 , this is just an extra test case

Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
/// <reference path='fourslash.ts'/>

// @strict: true

//// class A<T extends number = number> {
//// value!: T;
//// child!: InstanceType<typeof A.B<A<T>>>;
////
//// static B = class B<T extends A> {
//// parent!: T;
//// };
//// }
////
//// var a = new A();
////
//// a.child.parent.value/**/;

verify.quickInfoAt("", "(property) A<number>.value: number");
verify.getSemanticDiagnostics([]);