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Include index signatures of the source in mapped type template target inferences #29253

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Merged
weswigham merged 1 commit into from
Jan 25, 2019
Merged

Include index signatures of the source in mapped type template target inferences #29253

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7 changes: 6 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14438,7 +14438,12 @@ namespace ts {
priority |= InferencePriority.MappedTypeConstraint;
inferFromTypes(getIndexType(source), constraintType);
priority = savePriority;
inferFromTypes(getUnionType(map(getPropertiesOfType(source), getTypeOfSymbol)), getTemplateTypeFromMappedType(<MappedType>target));
const valueTypes = compact([
getIndexTypeOfType(source, IndexKind.String),
getIndexTypeOfType(source, IndexKind.Number),
...map(getPropertiesOfType(source), getTypeOfSymbol)
]);
inferFromTypes(getUnionType(valueTypes), getTemplateTypeFromMappedType(<MappedType>target));
return true;
}
return false;
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7 changes: 5 additions & 2 deletions src/compiler/core.ts
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Expand Up @@ -884,8 +884,11 @@ namespace ts {
/**
* Compacts an array, removing any falsey elements.
*/
export function compact<T>(array: T[]): T[];
export function compact<T>(array: ReadonlyArray<T>): ReadonlyArray<T>;
export function compact<T>(array: (T | undefined | null | false | 0 | "")[]): T[];
export function compact<T>(array: ReadonlyArray<T | undefined | null | false | 0 | "">): ReadonlyArray<T>;
// TSLint thinks these can be combined with the above - they cannot; they'd produce higher-priority inferences and prevent the falsey types from being stripped
export function compact<T>(array: T[]): T[]; // tslint:disable-line unified-signatures
export function compact<T>(array: ReadonlyArray<T>): ReadonlyArray<T>; // tslint:disable-line unified-signatures
export function compact<T>(array: T[]): T[] {
let result: T[] | undefined;
if (array) {
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8 changes: 8 additions & 0 deletions tests/baselines/reference/mappedToToIndexSignatureInference.js
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@@ -0,0 +1,8 @@
//// [mappedToToIndexSignatureInference.ts]
declare const fn: <K extends string, V>(object: { [Key in K]: V }) => object;
declare const a: { [index: string]: number };
fn(a);


//// [mappedToToIndexSignatureInference.js]
fn(a);
18 changes: 18 additions & 0 deletions tests/baselines/reference/mappedToToIndexSignatureInference.symbols
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@@ -0,0 +1,18 @@
=== tests/cases/compiler/mappedToToIndexSignatureInference.ts ===
declare const fn: <K extends string, V>(object: { [Key in K]: V }) => object;
>fn : Symbol(fn, Decl(mappedToToIndexSignatureInference.ts, 0, 13))
>K : Symbol(K, Decl(mappedToToIndexSignatureInference.ts, 0, 19))
>V : Symbol(V, Decl(mappedToToIndexSignatureInference.ts, 0, 36))
>object : Symbol(object, Decl(mappedToToIndexSignatureInference.ts, 0, 40))
>Key : Symbol(Key, Decl(mappedToToIndexSignatureInference.ts, 0, 51))
>K : Symbol(K, Decl(mappedToToIndexSignatureInference.ts, 0, 19))
>V : Symbol(V, Decl(mappedToToIndexSignatureInference.ts, 0, 36))

declare const a: { [index: string]: number };
>a : Symbol(a, Decl(mappedToToIndexSignatureInference.ts, 1, 13))
>index : Symbol(index, Decl(mappedToToIndexSignatureInference.ts, 1, 20))

fn(a);
>fn : Symbol(fn, Decl(mappedToToIndexSignatureInference.ts, 0, 13))
>a : Symbol(a, Decl(mappedToToIndexSignatureInference.ts, 1, 13))

14 changes: 14 additions & 0 deletions tests/baselines/reference/mappedToToIndexSignatureInference.types
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@@ -0,0 +1,14 @@
=== tests/cases/compiler/mappedToToIndexSignatureInference.ts ===
declare const fn: <K extends string, V>(object: { [Key in K]: V }) => object;
>fn : <K extends string, V>(object: { [Key in K]: V; }) => object
>object : { [Key in K]: V; }

declare const a: { [index: string]: number };
>a : { [index: string]: number; }
>index : string

fn(a);
>fn(a) : object
>fn : <K extends string, V>(object: { [Key in K]: V; }) => object
>a : { [index: string]: number; }

3 changes: 3 additions & 0 deletions tests/cases/compiler/mappedToToIndexSignatureInference.ts
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@@ -0,0 +1,3 @@
declare const fn: <K extends string, V>(object: { [Key in K]: V }) => object;
declare const a: { [index: string]: number };
fn(a);