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go/parser: bad error recovery for simple program with missing function name #63834

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griesemer opened this issue Oct 30, 2023 · 4 comments
Open

go/parser: bad error recovery for simple program with missing function name #63834

griesemer opened this issue Oct 30, 2023 · 4 comments
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gopls/parsing Issues related to parsing / poor parser recovery. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@griesemer
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package p

func (x string) []byte {
        return []byte(x)
}

produces (when run as test under go/types):

    check_test.go:168: testdata/manual.go:10:17: expected 'IDENT', found '['
    check_test.go:168: testdata/manual.go:10:18: expected '(', found ']'
    check_test.go:168: testdata/manual.go:10:24: missing ',' in parameter list
    check_test.go:168: testdata/manual.go:11:9: expected ')', found 'return'
    check_test.go:168: testdata/manual.go:11:17: missing ',' in parameter list
    check_test.go:168: testdata/manual.go:11:25: missing ',' before newline in parameter list
    check_test.go:168: testdata/manual.go:12:1: expected ')', found '}'
    check_test.go:168: testdata/manual.go:12:1: missing ',' in parameter list
    check_test.go:168: testdata/manual.go:12:2: expected ')', found 'EOF'
    check_test.go:168: testdata/manual.go:12:2: expected ')', found newline
    check_test.go:168: testdata/manual.go:12:2: expected ';', found 'EOF'
    check_test.go:168: testdata/manual.go:12:2: missing ',' before newline in parameter list

This may be easy to address.

cc: @findleyr
@griesemer griesemer added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Oct 30, 2023
@griesemer griesemer added this to the Backlog milestone Oct 30, 2023
@griesemer
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For the reference, the syntax parser produces just one error (also run under types2 test harness):

    check_test.go:157: testdata/manual.go:10:17: syntax error: unexpected [, expected name

(but then types2 crashes).

@lucasgpulcinelli
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Hi, first time contributor here
Is there someone working on this issue? It seems that the parseFuncDecl function in the go/parser package does not check syntax errors during function declaration if it does not conform to the usual two forms (methods and usual functions), and that is causing the cascade of errors seen.

Me and some colleagues would be interested in solving this

@griesemer
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@lucasgpulcinelli Nobody is working on this at the moment. Feel free to give it a shot. One word of caution, if I may: whatever your potential fix, please don't simply look for the particular pattern causing the problem here - it's an easy pitfall. As an aside, you might also want to look at cmd/compile/internal/syntax/parser.go which has better error recovery. Thanks.

@findleyr findleyr added the gopls/parsing Issues related to parsing / poor parser recovery. label Nov 17, 2023
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Change https://go.dev/cl/545075 mentions this issue: go/parser: improve error detection while parsing functions

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