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Merged
ahejlsberg merged 15 commits into from
Feb 1, 2019
Merged

Infer contextual types from generic return types #29478

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1b4bce2
Infer contextual types from return types through generic functions
ahejlsberg Jan 17, 2019
da9feca
Accept new baselines
ahejlsberg Jan 17, 2019
bb1c91f
Remove literal freshness when contextual type is a literal type
ahejlsberg Jan 18, 2019
4163d2d
Add tests
ahejlsberg Jan 18, 2019
c809002
Accept new baselines
ahejlsberg Jan 18, 2019
0b366ce
Address CR feedback
ahejlsberg Jan 18, 2019
0b1da02
Add missing return statements (ugh)
ahejlsberg Jan 19, 2019
60e7528
No union type reductions in contextual types
ahejlsberg Jan 20, 2019
dbea08f
Accept new baselines
ahejlsberg Jan 20, 2019
cf479fc
Add regression test for #29168
ahejlsberg Jan 20, 2019
2ea0251
Accept new baselines
ahejlsberg Jan 20, 2019
7c1bb14
Merge branch 'master' into fixContextualReturnTypes
ahejlsberg Jan 26, 2019
fffd774
Merge branch 'master' into fixContextualReturnTypes
ahejlsberg Feb 1, 2019
c581575
Add breaking change repros
ahejlsberg Feb 1, 2019
42be36d
Accept new baselines
ahejlsberg Feb 1, 2019
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Infer contextual types from return types through generic functions
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@ahejlsberg
ahejlsberg committed Jan 17, 2019
commit 1b4bce236eeb2dc6ed0f3a5467b15f5bedeb2dfa
46 changes: 30 additions & 16 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14591,18 +14591,18 @@ namespace ts {
}

function inferFromProperties(source: Type, target: Type) {
if (isTupleType(source)) {
if (isArrayType(source) || isTupleType(source)) {
if (isTupleType(target)) {
const sourceLength = getLengthOfTupleType(source);
const sourceLength = isTupleType(source) ? getLengthOfTupleType(source) : 0;
const targetLength = getLengthOfTupleType(target);
const sourceRestType = getRestTypeOfTupleType(source);
const sourceRestType = isTupleType(source) ? getRestTypeOfTupleType(source) : getElementTypeOfArrayType(source);
const targetRestType = getRestTypeOfTupleType(target);
const fixedLength = targetLength < sourceLength || sourceRestType ? targetLength : sourceLength;
for (let i = 0; i < fixedLength; i++) {
inferFromTypes(i < sourceLength ? source.typeArguments![i] : sourceRestType!, target.typeArguments![i]);
inferFromTypes(i < sourceLength ? (<TypeReference>source).typeArguments![i] : sourceRestType!, target.typeArguments![i]);
}
if (targetRestType) {
const types = fixedLength < sourceLength ? source.typeArguments!.slice(fixedLength, sourceLength) : [];
const types = fixedLength < sourceLength ? (<TypeReference>source).typeArguments!.slice(fixedLength, sourceLength) : [];
if (sourceRestType) {
types.push(sourceRestType);
}
Expand Down Expand Up @@ -17694,14 +17694,28 @@ namespace ts {
// Return the contextual type for a given expression node. During overload resolution, a contextual type may temporarily
// be "pushed" onto a node using the contextualType property.
function getApparentTypeOfContextualType(node: Expression): Type | undefined {
let contextualType = getContextualType(node);
contextualType = contextualType && mapType(contextualType, getApparentType);
if (contextualType && contextualType.flags & TypeFlags.Union) {
if (isObjectLiteralExpression(node)) {
return discriminateContextualTypeByObjectMembers(node, contextualType as UnionType);
const contextualType = instantiateContextualType(getContextualType(node), node);
if (contextualType) {
const apparentType = mapType(contextualType, getApparentType);
if (apparentType.flags & TypeFlags.Union) {
if (isObjectLiteralExpression(node)) {
return discriminateContextualTypeByObjectMembers(node, apparentType as UnionType);
}
else if (isJsxAttributes(node)) {
return discriminateContextualTypeByJSXAttributes(node, apparentType as UnionType);
}
}
else if (isJsxAttributes(node)) {
return discriminateContextualTypeByJSXAttributes(node, contextualType as UnionType);
return apparentType;
}
}

// If the given contextual type constains instantiable types and if a mapper representing

@jack-williams jack-williams Jan 19, 2019

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constains -> contains

// return type inferences is available, instantiate those types using that mapper.
function instantiateContextualType(contextualType: Type | undefined, node: Expression): Type | undefined {
if (contextualType && maybeTypeOfKind(contextualType, TypeFlags.Instantiable)) {
const returnMapper = (<InferenceContext>getContextualMapper(node)).returnMapper;
if (returnMapper) {
return mapType(contextualType, t => t.flags & TypeFlags.Instantiable ? instantiateType(t, returnMapper) : t);

@weswigham weswigham Jan 18, 2019

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This mapType call should probably have it's third argument set since we're in contextual typing and preserving string | "x"'s literaliness is desirable.

@weswigham weswigham Jan 18, 2019

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Also: I'm wondering why bother with the map type/instantiate flag check at all - instantiateType is only going to instantiate instantiable types anyway.

@jack-williams jack-williams Jan 18, 2019 •
edited
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If you change the mapType I think you can go ahead and close #29174.

(or ping me and I’ll close it)

@ahejlsberg ahejlsberg Jan 18, 2019

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@weswigham Agreed, we should make sure we use UnionReduction.None. The reason we don't just call instantiateType is that getContextualMapper isn't a super cheap operation and also that we don't want to instantiate contained object types as it is unnecessary and can be expensive.

@jack-williams I'll fix it so we don't need #29174.

@jack-williams jack-williams Jan 18, 2019

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@ahejlsberg Grand, closing the PR. Might be worth adding the example from #29168 to this PR, just to make sure it’s fixed.

}
}
return contextualType;
Expand Down Expand Up @@ -19847,6 +19861,9 @@ namespace ts {
const inferenceTargetType = getReturnTypeOfSignature(signature);
// Inferences made from return types have lower priority than all other inferences.
inferTypes(context.inferences, inferenceSourceType, inferenceTargetType, InferencePriority.ReturnType);
// Create a type mapper for instantiating generic contextual types using the inferences made
// from the return type.
context.returnMapper = cloneTypeMapper(context);
}
}

Expand Down Expand Up @@ -23022,12 +23039,9 @@ namespace ts {
}

function checkExpressionForMutableLocation(node: Expression, checkMode: CheckMode | undefined, contextualType?: Type, forceTuple?: boolean): Type {
if (arguments.length === 2) {
contextualType = getContextualType(node);
}
const type = checkExpression(node, checkMode, forceTuple);
return isTypeAssertion(node) ? type :
getWidenedLiteralLikeTypeForContextualType(type, contextualType);
getWidenedLiteralLikeTypeForContextualType(type, instantiateContextualType(arguments.length === 2 ? getContextualType(node) : contextualType, node));
}

function checkPropertyAssignment(node: PropertyAssignment, checkMode?: CheckMode): Type {
Expand Down
1 change: 1 addition & 0 deletions src/compiler/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4364,6 +4364,7 @@ namespace ts {
inferences: InferenceInfo[]; // Inferences made for each type parameter
flags: InferenceFlags; // Inference flags
compareTypes: TypeComparer; // Type comparer function
returnMapper?: TypeMapper; // Type mapper for inferences from return types (if any)
}

/* @internal */
Expand Down