x/tools/internal/gcimporter: TestIExportData_stdlib test fails with GOTOOLCHAIN override

[hyangah]

I use GOTOOLCHAIN to switch toolchain version. (easiest, recommended way to pick up latest go toolchain inside google).

$ GOTOOLCHAIN=local go version
go version go1.25.6 darwin/arm64
$ go env -changed
GOTOOLCHAIN='go1.26.2+auto'

This specific test doesn't work with this arrangement.

--- FAIL: TestIExportData_stdlib (0.02s)
    iexport_test.go:73: err: exit status 1: stderr: go: overlay contains a replacement for /Users/hyangah/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.26.2.darwin-arm64/src/errors/bad.go. Files beneath GOMODCACHE (/Users/hyangah/go/pkg/mod) must not be replaced.

[gabyhelp]

Related Issues

• cmd/go: toolchain escape via PATH in covermode when GOTOOLCHAIN auto-switches #77820
• x/tools/internal/gcimporter: TestImportTypeparamTests depends on `GOROOT/test/typeparam` #70081 (closed)
• cmd/go: test with `-overlay` failed with a go-vet error #50044 (closed)
• x/tools/go/packages: TestOverlayModFileChanges broken at head #33956 (closed)
• x/website: TestAPIVersion test fails when GOROOT is the toolchain module #78593

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[mwriter]

This seems to be a new change from Michael:
3f46587
It is meant to be used to detect cases where GOMODCACHE has been replaced. That replacement is not supported (GOMODCACHE is meant to be immutable) and the caller will use the information to return an error.

@hyangah

Apparently, Golang automatically downloaded this toolchain version and found himself trapped :D

[dr2chase]

@matloob

[adonovan]

That error message comes from go list via packages.Load, but the overlay in TestIExportData_stdlib specifies only the file GOROOT/src/errors/bad.go, so I don't know why it's triggering. Needs investigation.

[mwriter]

That error message comes from go list via packages.Load

I wonder how many times these names have come up in recent issues ;D
I would be very happy if a new topic in the Discussions were opened for these issues of package and module management.

[mwriter]

GOTOOLCHAIN=local
GOTOOLCHAIN='go1.26.2+auto'

By the way, I've come to the conclusion that the most reliable solution is version control via GOTOOLCHAIN=path and GOTOOLCHAIN=version+path.