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go/parser: goto; is incorrectly valid #70957

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mateusz834 opened this issue Dec 22, 2024 · 4 comments · May be fixed by #70958
Open

go/parser: goto; is incorrectly valid #70957

mateusz834 opened this issue Dec 22, 2024 · 4 comments · May be fixed by #70958
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@mateusz834
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NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.

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@mateusz834
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mateusz834 commented Dec 22, 2024 •
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While poking around the go/types internals, i noticed that nothing really "type-checks" gotos without labels.

First pass:

go/src/go/types/stmt.go

Lines 578 to 608 in 500675a

case *ast.BranchStmt:
if s.Label != nil {
check.hasLabel = true
return // checked in 2nd pass (check.labels)
}
switch s.Tok {
case token.BREAK:
if ctxt&breakOk == 0 {
check.error(s, MisplacedBreak, "break not in for, switch, or select statement")
}
case token.CONTINUE:
if ctxt&continueOk == 0 {
check.error(s, MisplacedContinue, "continue not in for statement")
}
case token.FALLTHROUGH:
if ctxt&fallthroughOk == 0 {
var msg string
switch {
case ctxt&finalSwitchCase != 0:
msg = "cannot fallthrough final case in switch"
case ctxt&inTypeSwitch != 0:
msg = "cannot fallthrough in type switch"
default:
msg = "fallthrough statement out of place"
}
check.error(s, MisplacedFallthrough, msg)
}
default:
check.errorf(s, InvalidSyntaxTree, "branch statement: %s", s.Tok)
}

Second pass:

go/src/go/types/labels.go

Lines 173 to 176 in 500675a

case *ast.BranchStmt:
if s.Label == nil {
return // checked in 1st pass (check.stmt)
}

Also it also turns out that:

func test() {
    goto;
}

Is accepted by the go/parser. The spec disallows gotos without labels, so we should either return an appropriate error in go/types or go/parser. Currently go/types returns an InvalidSyntaxTree error.

go/src/go/types/stmt.go

Lines 605 to 607 in 500675a

default:
check.errorf(s, InvalidSyntaxTree, "branch statement: %s", s.Tok)
}

CC @griesemer @adonovan
@gabyhelp
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(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

@mateusz834 mateusz834 added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Dec 22, 2024
@mateusz834
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Actually, this looks like a bug in go/parser:

go/src/go/parser/parser.go

Lines 2051 to 2056 in 500675a

pos := p.expect(tok)
var label *ast.Ident
if tok != token.FALLTHROUGH && p.tok == token.IDENT {
label = p.parseIdent()
}
p.expectSemi()

Will send a CL.

@mateusz834 mateusz834 self-assigned this Dec 22, 2024
@mateusz834
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cmd/compile/internal/syntax currently reports this as an error:

go/src/cmd/compile/internal/syntax/parser.go

Lines 2660 to 2667 in 500675a

case _Goto:
s := new(BranchStmt)
s.pos = p.pos()
s.Tok = _Goto
p.next()
s.Label = p.name()
return s

@mateusz834 mateusz834 linked a pull request Dec 22, 2024 that will close this issue
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Change https://go.dev/cl/638395 mentions this issue: go/parser: require label after goto

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go/parser: require label after goto mateusz834/go
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