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Limit inference from apparent types to one level deep (#27225)

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* Limit inference from apparent types to one level deep

* Rename marker & use booleanness not ===

* Undo typo
This commit is contained in:
Wesley Wigham 2018-09-20 15:00:17 -07:00 committed by GitHub
parent 67d8263b30
commit 928bff996f
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1 changed files with 10 additions and 1 deletions
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11
src/compiler/checker.ts
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@ -13439,6 +13439,7 @@ namespace ts {
let visited: Map<boolean>;
let contravariant = false;
let propagationType: Type;
let allowComplexConstraintInference = true;
inferFromTypes(originalSource, originalTarget);
function inferFromTypes(source: Type, target: Type): void {
@ -13616,7 +13617,15 @@ namespace ts {
// getApparentType can return _any_ type, since an indexed access or conditional may simplify to any other type.
// If that occurs and it doesn't simplify to an object or intersection, we'll need to restart `inferFromTypes`
// with the simplified source.
if (apparentSource !== source && !(apparentSource.flags & (TypeFlags.Object | TypeFlags.Intersection))) {
if (apparentSource !== source && allowComplexConstraintInference && !(apparentSource.flags & (TypeFlags.Object | TypeFlags.Intersection))) {
// TODO: The `allowComplexConstraintInference` flag is a hack! This forbids inference from complex constraints within constraints!
// This isn't required algorithmically, but rather is used to lower the memory burden caused by performing inference
// that is _too good_ in projects with complicated constraints (eg, fp-ts). In such cases, if we did not limit ourselves
// here, we might produce more valid inferences for types, causing us to do more checks and perform more instantiations
// (in addition to the extra stack depth here) which, in turn, can push the already close process over its limit.
// TL;DR: If we ever become generally more memory efficienct (or our resource budget ever increases), we should just
// remove this `allowComplexConstraintInference` flag.
allowComplexConstraintInference = false;
return inferFromTypes(apparentSource, target);
}
source = apparentSource;