Repository navigation
Cache inferences made from type arguments - #64553
Merged
Merged
Conversation
typescript-automation
Bot
added
Author: Team
For Uncommitted Bug
Copilot started reviewing on behalf of
Anders Hejlsberg (ahejlsberg)
September 30, 2026 15:30
View session
Contributor
There was a problem hiding this comment.
Copilot review overview
🟡 Changes recommended
The cache key omits propagation state, and the performance regression lacks direct test coverage.
Review effort: Balanced
Findings: 1
Open (2)
What changed in this PR
Caches type-argument inference for matching aliases and generic references to prevent exponential checking.
Changes:
- Extends inference cache keys with variance and priority state.
- Routes alias/reference inference through
invokeOnce. - Updates correlated-union tests for corrected inference behavior.
| File | Description |
|---|---|
tsc/internal/checker/inference.go |
Implements expanded inference caching. |
tsc/testdata/tests/cases/compiler/correlatedUnions.ts |
Uses NoInfer to preserve intended inference. |
tsc/testdata/baselines/reference/compiler/correlatedUnions.types |
Updates type baseline. |
tsc/testdata/baselines/reference/compiler/correlatedUnions.symbols |
Updates symbol baseline. |
tsc/testdata/baselines/reference/compiler/correlatedUnions.js |
Updates emit baseline. |
| // between the same pair of types. | ||
| func (c *Checker) invokeOnce(n *InferenceState, source *Type, target *Type, action func(c *Checker, n *InferenceState, source *Type, target *Type)) { | ||
| key := InferenceKey{s: source.id, t: target.id} | ||
| key := InferenceKey{source: source.id, target: target.id, priority: n.priority, contravariant: n.contravariant, bivariant: n.bivariant} |
| case source.objectFlags&ObjectFlagsReference != 0 && target.objectFlags&ObjectFlagsReference != 0 && (source.AsTypeReference().target == target.AsTypeReference().target || c.isArrayType(source) && c.isArrayType(target)) && !(source.AsTypeReference().node != nil && target.AsTypeReference().node != nil): | ||
| // If source and target are references to the same generic type, infer from type arguments | ||
| c.inferFromTypeArguments(n, c.getTypeArguments(source), c.getTypeArguments(target), c.getVariances(source.AsTypeReference().target)) | ||
| c.invokeOnce(n, source, target, (*Checker).inferFromReferenceTypeArguments) |
Member
Author
|
Oleksandr Tarasiuk (@a-tarasyuk) I have manually verified that this has the same effect on check times for the original repro and the test you included in #64388. Can you describe what goes on in that test? I'd like to understand before we include it. |
Member
Author
|
TypeScript Bot (@typescript-bot) test it |
Contributor
Contributor
|
Anders Hejlsberg (@ahejlsberg), the perf run you requested failed. You can check the log here. |
Contributor
|
Hey Anders Hejlsberg (@ahejlsberg), the results of running the DT tests are ready. Everything looks the same! |
Contributor
|
Anders Hejlsberg (@ahejlsberg) Here are the results of running the user tests with tsc comparing Something interesting changed - please have a look. Details
|
Contributor
|
Anders Hejlsberg (@ahejlsberg) Here are the results of running the top 400 repos with tsc comparing Everything looks good! |
Member
Author
|
TypeScript Bot (@typescript-bot) perf test this faster |
Contributor
Member
Author
|
The change in the webpack user test is simply that we're inferring a different type now that there aren't dropped inferences. The errors themselves are actually follow-on errors from other issues in webpack (specifically here that use of values as types now require explicit |
Anders Hejlsberg (ahejlsberg)
requested a review
from Ryan Cavanaugh (RyanCavanaugh)
September 30, 2026 20:04
typescript-automation
Bot
added
For Backlog Bug
Anders Hejlsberg (ahejlsberg)
requested a review
from Jake Bailey (jakebailey)
September 30, 2026 20:05
Contributor
|
Anders Hejlsberg (@ahejlsberg) Here they are:
tscComparison Report - baseline..pr
System info unknown
Hosts
Scenarios
Developer Information: |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Jake Bailey (jakebailey)
approved these changes
Sep 30, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
With this PR we cache inferences made from type arguments of references to the same alias or class/interface. The PR supersedes #64388 which implements similar caching, but does so through a separate cache instead of leveraging the existing
invokeOncecaching infrastructure.The PR fixes an issue with the existing cache where
priority,contravariant, andbivariantstates weren't included in the cache key. This would cause false matches and lead to dropped inferences. This fix revealed a test case incorrelatedUnions.tsthat incorrectly depended on dropped inferences and now requires use ofNoInfer<T>. The issue can be observed by the error in this version of the test that simply reverses the declaration order ofletterandcallerin theLetterCallertype.Thanks Oleksandr Tarasiuk (@a-tarasyuk) for researching the root cause and fix for the issue in #64378.
Fixes #64378.