microsoft/TypeScript
1
0
Fork 0
mirror of https://github.com/microsoft/TypeScript.git synced 2026-05-15 04:43:37 -05:00
Code Issues Packages Projects Releases 212 Wiki Activity

Improve logic for choosing between co- and contra-variant inferences (#46392)

Browse Source 
* Improve logic for choosing between co- and contra-variant inferences

* Add tests
This commit is contained in:
Anders Hejlsberg
2021-10-19 09:58:10 -07:00
committed by GitHub
parent fd6552a3c2
commit 56b6279818
5 changed files with 332 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
src/compiler/checker.ts
View File

@@ -22329,12 +22329,11 @@ namespace ts {
if (signature) {
const inferredCovariantType = inference.candidates ? getCovariantInference(inference, signature) : undefined;
if (inference.contraCandidates) {
const inferredContravariantType = getContravariantInference(inference);
// If we have both co- and contra-variant inferences, we prefer the contra-variant inference
// unless the co-variant inference is a subtype and not 'never'.
// unless the co-variant inference is a subtype of some contra-variant inference and not 'never'.
inferredType = inferredCovariantType && !(inferredCovariantType.flags & TypeFlags.Never) &&
isTypeSubtypeOf(inferredCovariantType, inferredContravariantType) ?
inferredCovariantType : inferredContravariantType;
some(inference.contraCandidates, t => isTypeSubtypeOf(inferredCovariantType, t)) ?
inferredCovariantType : getContravariantInference(inference);
}
else if (inferredCovariantType) {
inferredType = inferredCovariantType;