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gopls: prevent crash in ExtractToNewFile when bounds are invalid#645

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AmSach:fix/70553-slice-bounds-out-of-range
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gopls: prevent crash in ExtractToNewFile when bounds are invalid#645
AmSach wants to merge 1 commit into
golang:masterfrom
AmSach:fix/70553-slice-bounds-out-of-range

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@AmSach AmSach commented Apr 27, 2026

Fix for golang/go#70553

Problem

In ExtractToNewFile, the bounds checks at lines 118-124 called bug.Reportf but then continued execution. When safetoken.Offset returned an error that was ignored by CheckPos, the subsequent slice pgf.Src[start-fileStart:end-fileStart] would panic with "slice bounds out of range".

Fix

Replace bug.Reportf with return nil, bug.Errorf so the function exits safely with an error instead of crashing.

Also fix the comparison 0 <= start-fileStart which requires casting the token.Pos difference to int.

Testing

Go syntax check passes. The fix ensures bounds checks guard the slice operation.

Issue Reference

Fixes golang/go#70553

@AmSach
gopls: prevent crash in ExtractToNewFile when bounds are invalid
c413f88 
The bounds checks in ExtractToNewFile called bug.Reportf but then
continued execution, leading to a panic when slicing pgf.Src with
invalid bounds. Since CheckPos calls safetoken.Offset which can return
an error that is ignored, the subsequent slice pgf.Src[start-fileStart:end-fileStart]
at line 126 could crash with 'slice bounds out of range'.

Fix by replacing bug.Reportf with return nil, bug.Errorf so the
function exits safely with an error instead of crashing.

Also fix the comparison 0 <= start-fileStart which requires casting
token.Pos difference to int.

Fixes golang/go#70553
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gopherbot commented Apr 27, 2026

This PR (HEAD: c413f88) has been imported to Gerrit for code review.

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gopherbot commented Apr 27, 2026

Message from Gopher Robot:

Patch Set 1:

(1 comment)

Please don’t reply on this GitHub thread. Visit golang.org/cl/770980.
After addressing review feedback, remember to publish your drafts!

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gopherbot commented Apr 27, 2026

Message from Gopher Robot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
A maintainer will review your change and provide feedback. See
https://go.dev/doc/contribute#review for more info and tips to get your
patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

Please don’t reply on this GitHub thread. Visit golang.org/cl/770980.
After addressing review feedback, remember to publish your drafts!

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gopherbot commented Apr 28, 2026

Message from Alan Donovan:

Patch Set 1:

(1 comment)

Please don’t reply on this GitHub thread. Visit golang.org/cl/770980.
After addressing review feedback, remember to publish your drafts!

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x/tools/gopls: "slice bounds out of range" crash in ExtractToNewFile

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