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Make isTypeAssignableTo public on TypeChecker #56448

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merged 3 commits into from
Dec 8, 2023
Merged

Make isTypeAssignableTo public on TypeChecker #56448

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335cea4
Export isTypeAssignableTo on TypeChecker
jakebailey Nov 17, 2023
1ef7d15
Add some sort of docstring
jakebailey Nov 17, 2023
7ad4e52
Merge branch 'main' into export-isTypeAssignableTo
jakebailey Dec 8, 2023
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15 changes: 14 additions & 1 deletion src/compiler/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5158,7 +5158,20 @@ export interface TypeChecker {
/** @internal */ getPromiseLikeType(): Type;
/** @internal */ getAsyncIterableType(): Type | undefined;

/** @internal */ isTypeAssignableTo(source: Type, target: Type): boolean;
/**
* Returns true if the "source" type is assignable to the "target" type.
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Suggested change
* Returns true if the "source" type is assignable to the "target" type.
* Returns true if the `source` type is assignable to the `target` type.

*
* ```ts
* declare const abcLiteral: ts.Type; // Type of "abc"
* declare const stringType: ts.Type; // Type of string
*
* isTypeAssignableTo(abcLiteral, abcLiteral); // true; "abc" is assignable to "abc"
* isTypeAssignableTo(abcLiteral, stringType); // true; "abc" is assignable to string
* isTypeAssignableTo(stringType, abcLiteral); // false; string is not assignable to "abc"
* isTypeAssignableTo(stringType, stringType); // true; string is assignable to string
* ```
*/
isTypeAssignableTo(source: Type, target: Type): boolean;
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This needs a doc; please leave suggestions!

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Thinking on what I'd want as a user, it's mostly just knowing what kind of caching I'd have to worry about (since that was brought up by TS folks previously) and examples of what direction the assignability runs in. Vaguely:

/**
 * Performs an assignability check, including using persistent caches.
 * @returns Whether `source` is assignable to `type`.
 * @example
 * ```ts
 * declare const literal: ts.Type; // Type of "abc"
 * declare const primitive: ts.Type; // Type of string
 * isTypeAssignableTo(literal, literal); // true
 * isTypeAssignableTo(literal, primitive); // true
 * isTypeAssignableTo(primitive, literal); // false
 * isTypeAssignableTo(primitive, primitive); // true
 * ```

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Added something similar to the above.

/** @internal */ createAnonymousType(symbol: Symbol | undefined, members: SymbolTable, callSignatures: Signature[], constructSignatures: Signature[], indexInfos: IndexInfo[]): Type;
/** @internal */ createSignature(
declaration: SignatureDeclaration | undefined,
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14 changes: 14 additions & 0 deletions tests/baselines/reference/api/typescript.d.ts
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Expand Up @@ -6832,6 +6832,20 @@ declare namespace ts {
* is `never`. Instead, use `type.flags & TypeFlags.Never`.
*/
getNeverType(): Type;
/**
* Returns true if the "source" type is assignable to the "target" type.
*
* ```ts
* declare const abcLiteral: ts.Type; // Type of "abc"
* declare const stringType: ts.Type; // Type of string
*
* isTypeAssignableTo(abcLiteral, abcLiteral); // true; "abc" is assignable to "abc"
* isTypeAssignableTo(abcLiteral, stringType); // true; "abc" is assignable to string
* isTypeAssignableTo(stringType, abcLiteral); // false; string is not assignable to "abc"
* isTypeAssignableTo(stringType, stringType); // true; string is assignable to string
* ```
*/
isTypeAssignableTo(source: Type, target: Type): boolean;
/**
* True if this type is the `Array` or `ReadonlyArray` type from lib.d.ts.
* This function will _not_ return true if passed a type which
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