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Restrict widening of literal types in type argument inference

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This commit is contained in:
Anders Hejlsberg 2016-09-02 09:42:58 -07:00
parent 2a60f79869
commit b3c9571d6f
1 changed files with 7 additions and 5 deletions
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12
src/compiler/checker.ts
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@ -7506,7 +7506,7 @@ namespace ts {
function hasPrimitiveConstraint(type: TypeParameter): boolean {
const constraint = getConstraintOfTypeParameter(type);
return constraint && (constraint.flags & (TypeFlags.String | TypeFlags.Number | TypeFlags.Boolean | TypeFlags.Enum)) !== 0;
return constraint && maybeTypeOfKind(constraint, TypeFlags.Primitive);
}
function inferTypes(context: InferenceContext, source: Type, target: Type) {
@ -7515,7 +7515,10 @@ namespace ts {
let depth = 0;
let inferiority = 0;
const visited = createMap<boolean>();
inferFromTypes(source, target);
// We widen a literal source type only if we're inferring directly to a type parameter
// that has no primitive or literal constraint.
const shouldWiden = isLiteralType(source) && target.flags & TypeFlags.TypeParameter && !hasPrimitiveConstraint(<TypeParameter>target);
inferFromTypes(shouldWiden ? getBaseTypeOfLiteralType(source) : source, target);
function isInProcess(source: Type, target: Type) {
for (let i = 0; i < depth; i++) {
@ -7584,9 +7587,8 @@ namespace ts {
inferences.secondary || (inferences.secondary = []) :
inferences.primary || (inferences.primary = []);
// Infer base primitive type for unit types.
const widened = isUnitType(source) && !hasPrimitiveConstraint(<TypeParameter>target) ? getBaseTypeOfLiteralType(source) : source;
if (!contains(candidates, widened)) {
candidates.push(widened);
if (!contains(candidates, source)) {
candidates.push(source);
}
}
return;