fix: Corsa differences in `export=` module augmentation by pratheeknathani · Pull Request #4446 · microsoft/typescript-go

pratheeknathani · 2026-06-25T20:15:38Z

Summary

Test setup: // /node_modules/foo/index.d.ts export = foo; declare namespace foo { export type T = number; } // /a.ts import * as foo from "foo"; declare module "foo" { export function f(): T; // OK in TS } Corsa wrongly reported TS4060: Return type of exported function has or is using private name 'T' when emitting...

What changed

Test setup:

// /node_modules/foo/index.d.ts
export = foo;
declare namespace foo {
 export type T = number;
}

// /a.ts
import * as foo from "foo";
declare module "foo" {
 export function f(): T; // OK in TS
}

Corsa wrongly reported TS4060: Return type of exported function has or is using private name 'T' when emitting a.d.ts. As a result a.d.ts was never emitted.

During declaration emit, T is resolved correctly, but its visibility is checked through its container, the namespace foo. foo is not marked export; it is exported only through export = foo in index.d.ts. TypeScript makes such an export = target visible by calling collectLinkedAliases(id, /*setVisibility*/ true) inside checkExportAssignment, which runs while checking every file, including non-emitted ones like index.d.ts.

Corsa moved that alias-visibility marking into the emit resolver (PrecalculateDeclarationEmitVisibility), which only walks the file currently being emitted (a.ts/b.ts). The export = foo lives in index.d.ts, which is never emitted, so foo (and therefore T) was never marked visible. determineIfDeclarationIsVisible then fell through to isGlobalSourceFile(parent) and returned false, producing the spurious TS4060.

Issue

Fixes #3481

Issue: #3481

Diffstat

internal/checker/emitresolver.go | 26 +++++++++++++++++++++
 ...signmentMembersVisibleInAugmentation.errors.txt | 23 ------------------
 ...exportAssignmentMembersVisibleInAugmentation.js | 5 ++++
 ...tAssignmentMembersVisibleInAugmentation.js.diff | 14 -----------
 ...entMembersVisibleInAugmentation.errors.txt.diff | 27 ----------------------
 5 files changed, 31 insertions(+), 64 deletions(-)

Testing

Ran the relevant tests and linter for the changed files while developing.
Kept the change minimal and focused on this one issue.

AI assistance

I used GitHub Copilot to help write parts of this change. I've reviewed and tested it myself, I understand what it does, and I'll follow up on any review feedback.

Fixes microsoft#3481

Copilot

Pull request overview

Fixes a declaration-emit visibility edge case where an export = target (and its nested exported members) wasn’t treated as externally visible during .d.ts emit, causing a spurious TS4060 and preventing declaration output for a module augmentation scenario.

Changes:

Treat declarations that are the target of an export = in their containing external module as visible during declaration emit visibility checks.
Update submodule baselines to remove the erroneous TS4060 diagnostic and restore a.d.ts emission for the affected test.
Remove now-unneeded triaged diff baselines for this case.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/checker/emitresolver.go	Adds an `export =`-target visibility fast-path in `determineIfDeclarationIsVisible`.
testdata/baselines/reference/submoduleTriaged/compiler/exportAssignmentMembersVisibleInAugmentation.errors.txt.diff	Removes the triaged diff that captured the now-fixed TS4060 discrepancy.
testdata/baselines/reference/submodule/compiler/exportAssignmentMembersVisibleInAugmentation.errors.txt	Removes the error baseline now that TS4060 no longer occurs.
testdata/baselines/reference/submodule/compiler/exportAssignmentMembersVisibleInAugmentation.js	Updates baseline to include the restored `a.d.ts` output.
testdata/baselines/reference/submodule/compiler/exportAssignmentMembersVisibleInAugmentation.js.diff	Removes the diff baseline since the output now matches the reference expectation.

jakebailey · 2026-06-25T20:31:50Z

-        export function f(): T; // OK
-                             ~
-!!! error TS4060: Return type of exported function has or is using private name 'T'.


Odd that this begins working

Yeah, this lines up with what upstream TypeScript already does here (which is why there was a submoduleTriaged diff recording Corsa diverging from it).

TS marks foo/T visible via collectLinkedAliases(setVisibility=true) on the export = foo in index.d.ts, but Corsa moved that into PrecalculateDeclarationEmitVisibility, which only walks the file being emitted (a.ts), so the export = in the never-emitted index.d.ts was missed and the target fell through to isGlobalSourceFile and returned false. The fix just treats a declaration that's the export = target of its own module as visible, so it matches TS again.

This sort of cross-file analysis is very spooky... It means emit can differ based on whether or not we use the checker for emit or not. Probably that is inevitable for this particular location, however

jakebailey · 2026-06-25T20:44:08Z

@typescript-bot perf test this faster

typescript-automation · 2026-06-25T20:44:13Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test this faster`	✅ Started	👀 Results

typescript-automation · 2026-06-25T21:07:15Z

@jakebailey
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄	₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{81,773 (± 0.05%)}	_{81,811 (± 0.04%)}	_~	_81,770	_81,853	_{p=0.128 n=6}
_Types	_98,821	_98,821	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{180,225k (± 0.33%)}	_{179,941k (± 0.28%)}	_~	_179,281k	_180,780k	_{p=0.230 n=6}
_{Memory Allocs}	_{2,547,020 (± 0.01%)}	_{2,547,001 (± 0.01%)}	_~	_2,546,688	_2,547,441	_{p=0.936 n=6}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.066s (± 8.59%)}	_{0.063s (± 5.69%)}	_~	_0.059s	_0.067s	_{p=0.466 n=6}
_{Bind Time}	_{0.018s (±30.58%)}	_{0.016s (±24.36%)}	_~	_0.011s	_0.023s	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.872s (± 1.13%)}	_{0.869s (± 0.28%)}	_~	_0.864s	_0.871s	_{p=0.686 n=6}
_{Total Time}	_{0.957s (± 1.40%)}	_{0.949s (± 0.96%)}	_~	_0.935s	_0.963s	_{p=0.336 n=6}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{876,226 (± 0.10%)}	_{877,045 (± 0.17%)}	_~	_875,879	_879,930	_{p=0.298 n=6}
_Types	_{263,750 (± 0.00%)}	_{263,750 (± 0.00%)}	_~	_263,748	_263,751	_{p=1.000 n=6}
_{Memory Used}	_{830,189k (± 0.05%)}	_{830,701k (± 0.07%)}	_~	_830,267k	_831,792k	_{p=0.128 n=6}
_{Memory Allocs}	_{12,654,301 (± 0.12%)}	_{12,650,638 (± 0.09%)}	_~	_12,639,416	_12,664,479	_{p=0.575 n=6}
_{Config Time}	_0.017s	_{0.017s (± 4.71%)}	_~	_0.017s	_0.019s	_{p=0.405 n=6}
_{Parse Time}	_{0.234s (± 4.58%)}	_{0.237s (± 4.30%)}	_~	_0.228s	_0.255s	_{p=0.419 n=6}
_{Bind Time}	_{0.054s (±19.40%)}	_{0.057s (±35.88%)}	_~	_0.036s	_0.087s	_{p=0.688 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{1.881s (± 0.77%)}	_{1.908s (± 1.93%)}	_~	_1.868s	_1.958s	_{p=0.471 n=6}
_{Total Time}	_{2.202s (± 0.64%)}	_{2.232s (± 1.04%)}	_{+0.030s (+ 1.36%)}	_2.207s	_2.260s	_{p=0.016 n=6}
_{mui-docs - native}
_Errors	_11,282	_{11,280 (± 0.04%)}	_~	_11,271	_11,282	_{p=0.074 n=6}
_Symbols	_4,747,930	_4,747,930	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,585,409	_1,585,409	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{5,883,975k (± 0.03%)}	_{5,882,408k (± 0.03%)}	_~	_5,879,606k	_5,885,692k	_{p=0.298 n=6}
_{Memory Allocs}	_{50,872,251 (± 0.14%)}	_{50,813,209 (± 0.06%)}	_~	_50,773,375	_50,858,662	_{p=0.093 n=6}
_{Config Time}	_{0.017s (± 9.79%)}	_{0.017s (± 6.94%)}	_~	_0.016s	_0.019s	_{p=0.445 n=6}
_{Parse Time}	_{0.529s (± 5.37%)}	_{0.545s (± 2.62%)}	_~	_0.525s	_0.561s	_{p=0.378 n=6}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{17.399s (± 0.38%)}	_{17.438s (± 0.67%)}	_~	_17.356s	_17.651s	_{p=0.470 n=6}
_{Emit Time}	_{0.524s (±30.36%)}	_{0.520s (±31.02%)}	_~	_0.430s	_0.847s	_{p=0.871 n=6}
_{Total Time}	_{19.278s (± 0.89%)}	_{19.287s (± 1.42%)}	_~	_19.091s	_19.824s	_{p=0.936 n=6}
_{self-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,394,269	_1,394,269	_~	_~	_~	_{p=1.000 n=6}
_Types	_442,235	_442,235	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{1,650,893k (± 0.33%)}	_{1,649,859k (± 0.29%)}	_~	_1,643,208k	_1,655,768k	_{p=0.810 n=6}
_{Memory Allocs}	_{98,387,513 (± 0.04%)}	_{98,396,273 (± 0.05%)}	_~	_98,336,835	_98,481,642	_{p=0.936 n=6}
_{Config Time}	_{0.026s (±15.49%)}	_{0.017s (±47.62%)}	_{🟩-0.009s (-34.81%)}	_0.007s	_0.027s	_{p=0.037 n=6}
_{Parse Time}	_{0.272s (± 4.54%)}	_{0.266s (± 4.89%)}	_~	_0.246s	_0.283s	_{p=0.470 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{2.336s (± 0.61%)}	_{2.326s (± 0.64%)}	_~	_2.310s	_2.354s	_{p=0.297 n=6}
_{Emit Time}	_{0.288s (± 2.23%)}	_{0.283s (± 3.40%)}	_~	_0.270s	_0.299s	_{p=0.297 n=6}
_{Total Time}	_{30.568s (± 0.64%)}	_{30.244s (± 1.16%)}	_~	_29.731s	_30.731s	_{p=0.093 n=6}
_{self-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_337,637	_337,637	_~	_~	_~	_{p=1.000 n=6}
_Types	_199,520	_199,520	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{332,423k (± 0.05%)}	_{332,469k (± 0.03%)}	_~	_332,328k	_332,628k	_{p=0.689 n=6}
_{Memory Allocs}	_{4,760,753 (± 0.02%)}	_{4,760,374 (± 0.01%)}	_~	_4,759,773	_4,760,776	_{p=0.471 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.131s (± 3.29%)}	_{0.125s (± 3.90%)}	_~	_0.120s	_0.133s	_{p=0.064 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{1.393s (± 0.95%)}	_{1.385s (± 0.58%)}	_~	_1.376s	_1.397s	_{p=0.297 n=6}
_{Emit Time}	_{0.125s (±11.12%)}	_{0.124s (± 3.79%)}	_~	_0.118s	_0.131s	_{p=1.000 n=6}
_{Total Time}	_{1.709s (± 1.23%)}	_{1.686s (± 0.47%)}	_{-0.022s (- 1.30%)}	_1.676s	_1.695s	_{p=0.037 n=6}
_{ts-pre-modules - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_97,488	_97,488	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₅₆	₃₅₆	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{133,703k (± 0.01%)}	_{133,731k (± 0.02%)}	_~	_133,698k	_133,764k	_{p=0.128 n=6}
_{Memory Allocs}	_{182,584 (± 0.20%)}	_{182,683 (± 0.14%)}	_~	_182,228	_182,911	_{p=0.378 n=6}
_{Config Time}	_{0.001s (±48.94%)}	_0.001s	_~	_~	_~	_{p=0.405 n=6}
_{Parse Time}	_{0.110s (± 3.54%)}	_{0.109s (± 4.86%)}	_~	_0.106s	_0.120s	_{p=0.807 n=6}
_{Bind Time}	_{0.038s (± 5.12%)}	_{0.035s (±15.33%)}	_~	_0.029s	_0.044s	_{p=0.142 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{0.152s (± 3.65%)}	_{0.148s (± 4.42%)}	_~	_0.142s	_0.156s	_{p=0.260 n=6}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_6,793,987	_6,793,987	_~	_~	_~	_{p=1.000 n=6}
_Types	_2,402,155	_2,402,155	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{4,619,034k (± 0.01%)}	_{4,619,215k (± 0.02%)}	_~	_4,617,943k	_4,620,572k	_{p=0.810 n=6}
_{Memory Allocs}	_{32,790,166 (± 0.04%)}	_{32,788,462 (± 0.03%)}	_~	_32,778,046	_32,802,967	_{p=0.936 n=6}
_{Config Time}	_{0.074s (±12.20%)}	_{0.074s (± 9.55%)}	_~	_0.068s	_0.084s	_{p=1.000 n=6}
_{Parse Time}	_{0.891s (± 3.76%)}	_{0.886s (± 2.80%)}	_~	_0.852s	_0.910s	_{p=0.873 n=6}
_{Bind Time}	_{0.145s (±14.31%)}	_{0.138s (± 2.53%)}	_~	_0.133s	_0.144s	_{p=1.000 n=6}
_{Check Time}	_{8.948s (± 0.65%)}	_{8.903s (± 0.29%)}	_~	_8.855s	_8.927s	_{p=0.054 n=6}
_{Emit Time}	_{2.471s (± 9.01%)}	_{2.483s (± 3.54%)}	_~	_2.322s	_2.575s	_{p=0.230 n=6}
_{Total Time}	_{12.548s (± 1.13%)}	_{12.501s (± 0.97%)}	_~	_12.293s	_12.639s	_{p=0.471 n=6}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_183,526	_183,526	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{223,356k (± 0.10%)}	_{223,412k (± 0.09%)}	_~	_223,162k	_223,580k	_{p=0.575 n=6}
_{Memory Allocs}	_{1,080,282 (± 0.35%)}	_{1,080,195 (± 0.47%)}	_~	_1,073,344	_1,087,827	_{p=0.936 n=6}
_{Config Time}	_{0.010s (±10.67%)}	_{0.012s (±14.99%)}	_~	_0.009s	_0.014s	_{p=0.051 n=6}
_{Parse Time}	_{0.155s (± 4.24%)}	_{0.155s (± 4.16%)}	_~	_0.146s	_0.163s	_{p=1.000 n=6}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.042s (±16.10%)}	_{0.036s (±20.54%)}	_~	_0.030s	_0.050s	_{p=0.108 n=6}
_{Total Time}	_{0.207s (± 3.56%)}	_{0.203s (± 5.72%)}	_~	_0.193s	_0.224s	_{p=0.261 n=6}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,065,147	_1,065,147	_~	_~	_~	_{p=1.000 n=6}
_Types	_389,312	_389,312	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{643,885k (± 0.02%)}	_{643,875k (± 0.01%)}	_~	_643,784k	_643,930k	_{p=0.689 n=6}
_{Memory Allocs}	_{5,103,085 (± 0.13%)}	_{5,098,278 (± 0.04%)}	_~	_5,095,997	_5,102,191	_{p=0.093 n=6}
_{Config Time}	_{0.005s (±11.05%)}	_{0.005s (± 8.44%)}	_~	_0.004s	_0.005s	_{p=0.595 n=6}
_{Parse Time}	_{0.131s (± 4.93%)}	_{0.139s (± 4.07%)}	_~	_0.132s	_0.148s	_{p=0.072 n=6}
_{Bind Time}	_{0.035s (±27.16%)}	_{0.035s (±25.34%)}	_~	_0.026s	_0.047s	_{p=0.688 n=6}
_{Check Time}	_{1.306s (± 1.59%)}	_{1.306s (± 1.03%)}	_~	_1.292s	_1.330s	_{p=0.810 n=6}
_{Emit Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.482s (± 1.09%)}	_{1.490s (± 1.14%)}	_~	_1.475s	_1.521s	_{p=0.336 n=6}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
self-build-src - native
self-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

The PR deleted submoduleTriaged/compiler/exportAssignmentMembersVisibleInAugmentation.errors.txt.diff (the diff is now resolved) but left its entry in testdata/submoduleTriaged.txt. TestSubmoduleTriagedFilesExist in internal/testutil/baseline asserts every listed file exists, so it failed across every go test ./... job (no-submodules, noembed, race, ubuntu, windows, concurrent, generate). Remove the stale line; the issue-3481 group keeps augmentExportEquals2.errors.txt.diff, which is still a tracked diff.

pratheeknathani · 2026-06-25T21:36:10Z

Pushed ad92cc3 to fix CI on this PR.

The earlier commit correctly deleted the now-resolved triaged baseline submoduleTriaged/compiler/exportAssignmentMembersVisibleInAugmentation.errors.txt.diff, but left its entry in testdata/submoduleTriaged.txt. TestSubmoduleTriagedFilesExist (in internal/testutil/baseline) asserts every listed file exists, so it failed across all go test ./... jobs (no-submodules, noembed, race, ubuntu, windows, concurrent, generate).

The follow-up removes that single stale line. The issue-3481 group still keeps augmentExportEquals2.errors.txt.diff, which remains a tracked diff. Verified locally with go test ./internal/testutil/baseline/ and the full testrunner suite (TestLocal + TestSubmodule).

fix: Corsa differences in export= module augmentation

c77babf

Fixes microsoft#3481

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fix: Corsa differences in `export=` module augmentation#4446

fix: Corsa differences in `export=` module augmentation#4446
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