8000 x/tools/gopls: Definition: out-of-bounds panic · Issue #73797 · golang/go · GitHub
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x/tools/gopls: Definition: out-of-bounds panic #73797
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adonovan opened this issue May 20, 2025 · 4 comments
Open

x/tools/gopls: Definition: out-of-bounds panic #73797

adonovan opened this issue May 20, 2025 · 4 comments
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@madelinekalil
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gopls/telemetry-wins gopls Issues related to the Go language server, gopls. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Tools This label describes issues relating to any tools in the x/tools repository.
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gopls/v0.19.0

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@adonovan
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#!stacks
"runtime.goPanicIndex:+2" && "Definition:+107"

Issue created by stacks.

	case token.BREAK, token.CONTINUE:
			// Find innermost relevant ancestor for break/continue.
			for i, n := range path[1:] {
				if isLabeled {
					l, ok := path[1:][i+1].(*ast.LabeledStmt) <--- panic (on last iteration of range loop, i+1 is OOB)
					if !(ok && l.Label.Name == label.Name()) {
						continue
					}
				}

This stack ChWbnw was reported by telemetry:

golang.org/x/tools/gopls@v0.18.1 go1.23.6 windows/amd64 vscode (2)
@adonovan adonovan added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. gopls Issues related to the Go language server, gopls. Tools This label describes issues relating to any tools in the x/tools repository. gopls/telemetry-wins labels May 20, 2025
@gopherbot gopherbot added this to the Unreleased milestone May 20, 2025
@ 8000 adonovan adonovan modified the milestones: Unreleased, gopls/v0.19.0 May 20, 2025
@madelinekalil
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madelinekalil commented May 20, 2025 •
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Was able to reproduce this with the following code:

func F() {
    label:
	for i := range 10 {
	}
	for i := range 10 {
		continue label
	}
}

This compiles but there is a typecheck error since the label corresponds to a different loop. With the path[1:][i+1].(*ast.LabeledStmt) check we are assuming we will find the label on the enclosing path, which is not the case for this example. I guess we just have to add a check that i has not exceeded the length of the path and if it has, return early.

@mateusz834
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This compiles but there is a typecheck error since the label corresponds to a different loop

Note that it only ends up with a typecheck error if you are using gotip to compile gopls.

See #70974

@gopherbot
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Change https://go.dev/cl/674497 mentions this issue: gopls/internal/golang: fix crash in definition of invalid "continue label"

@gopherbot
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Change https://go.dev/cl/675017 mentions this issue: gopls/internal/golang: fix crash in definition of invalid "continue label"

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@madelinekalil madelinekalil

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gopls/telemetry-wins gopls Issues related to the Go language server, gopls. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Tools This label describes issues relating to any tools in the x/tools repository.
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