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go/parser: wrong syntax error #2088

rsc opened this issue Jul 21, 2011 · 3 comments

go/parser: wrong syntax error #2088

rsc opened this issue Jul 21, 2011 · 3 comments


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rsc commented Jul 21, 2011

$ cat x.go
package main

func f() {
    x(%v: hi", y)
$ gofmt x.go
x.go:4:2: illegal label declaration
x.go:5:3: expected '}', found 'EOF'

The first error in this file is the %.
go/parser should say something about the %
before complaining about the colon indirectly
via the label declaration.

It may also be worth checking in the tokenizer
for strings with newlines.  That's often a
helpful thing to point out in addition to what
the parser sees.  Same for newline in character

$ 6g x.go
x.go:4: syntax error: unexpected %
x.go:4: newline in string
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Comment 1:

This issue is fixed with (pending) CL 4803047 ( ).
By default, the parser, gofmt, and gotype report at most one error per line as often
subsequent errors on a line are spurious follow-up errors. In this case, the parser
guesses the label declaration to start at the x and reports it as such but does not
report the erroneous % (because it's considered a spurious error).
Changed the label error reporting to use the '%' position instead. Now the first error
reported is for the '%':
gofmt test.go
test.go:4:7: expected operand, found '%'
test.go:5:2: expected '}', found 'EOF'
Also added a -e flag to gotype and gofmt to get all errors:
gofmt -e test.go
test.go:4:7: expected operand, found '%'
test.go:4:8: expected ')', found 'IDENT' v
test.go:4:9: illegal label declaration
test.go:4:11: expected ';', found 'IDENT' hi
test.go:4:13: string not terminated
test.go:5:2: expected '}', found 'EOF'
test.go:5:2: expected ';', found 'EOF'
The scanner always checked for newlines in strings (again, in this specific case that
error is only reported with the -e flag set).

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Comment 2:

Correction: The previous comment should have said:
"Changed the label error reporting to use the ':' position instead."

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Comment 3:

This issue was closed by revision fa49779.

Status changed to Fixed.

@rsc rsc added fixed labels Jul 22, 2011
@golang golang locked and limited conversation to collaborators Jun 24, 2016
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