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go/types: missing error on an edge-case with continue/break with labels #70974

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mateusz834 opened this issue Dec 23, 2024 · 4 comments · May be fixed by #70976
Open

go/types: missing error on an edge-case with continue/break with labels #70974

mateusz834 opened this issue Dec 23, 2024 · 4 comments · May be fixed by #70976
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@mateusz834
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NeedsFix The path to resolution is known, but the work has not been done.

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@mateusz834
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mateusz834 commented Dec 23, 2024 •
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Once again, because i am poking around with go/types internals, i have spotted a bug in the type-checker.

The code below type-checks without any error:

package test

func test() {
outer:
	for range "aa" {
		break outer
	}

	for range "aa" {
		break outer
	}
}

This happens because lstmt:

go/src/go/types/labels.go

Line 169 in b9955f0

lstmt = s

is assigned and never cleared, thus:

go/src/go/types/labels.go

Lines 234 to 236 in b9955f0

case *ast.BlockStmt:
blockBranches(lstmt, s.List)

is executed with a wrong label (for the second for statement).

CC @adonovan @griesemer
@mateusz834 mateusz834 added the NeedsFix The path to resolution is known, but the work has not been done. label Dec 23, 2024
@mateusz834
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I will send a CL for this.

@mateusz834 mateusz834 changed the title go/types: missing error on an edge-case with continue/break go/types: missing error on an edge-case with continue/break with labels Dec 23, 2024
@adonovan
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I'm curious: how are you finding these interesting bugs? Are you using a fuzzer, or just reading skeptically? Either way, impressive.

@mateusz834 mateusz834 linked a pull request Dec 23, 2024 that will close this issue
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@gopherbot
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Change https://go.dev/cl/638257 mentions this issue: go/types: propagate *ast.LabeledStmt in blockBranches properly

@mateusz834
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@adonovan I am working on a POC go/* fork tgoast, with a HTML-like syntax (it is a superset of Go, Go is a valid tgo (working name)). As I try to get the fork of types working, something told me that the current logic seemed wrong, after a few attempts, this bug came to my mind.

@mateusz834 mateusz834 self-assigned this Dec 24, 2024
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go/types: propagate *ast.LabeledStmt in blockBranches properly mateusz834/go
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@adonovan @gopherbot @mateusz834