Shift/reduce conflict in src/cmd/gc/go.y causes compile error at import #771
Description
by pwil3058:
$GOOS=linux
$GOARCH=amd64
Version: accc5a64ee63 tip
In the distribution directory, do:
LANG=C LANGUAGE="en_US.UTF8" bison -v -y src/cmd/gc/go.y
Expected output:
Actual output:
conflicts: 1 shift/reduce
This conflict can cause compile failure in exactly one way e.g.:
Copy the attached files: pkg1.go, pkg2.go, Makefile; to a directory:
make
Expected output:
6g pkg1.go
6g pkg2.go
Actual output:
6g pkg1.go
6g pkg2.go
pkg2.go:3: syntax error: unexpected }, expecting .
make: *** [all] Error 1
This failure is caused by line 16 in pkg1.go which is exactly the same as
line 9 except that it has a field tag which, together with the fact the
function type being declared has no return type, is the cause of the problem.
The problem is not triggered until the package in pkg1.go is imported by
pkg2.go (which is all it does).
Confirmation of this analysys can be made by commenting out the tag on
line 16 and running make. There will be no problems.
Analysis of src/cmd/gc/y.output indicates that the cause of the
shift/reduce conflict is summarised in the extracted subset in the attached
file conflict.y.
It can be further localised to the five (simplified) productions:
hidden_importsym:
LLITERAL '.' sym
hidden_structdcl:
sym hidden_type oliteral
oliteral: /* empty */
| LLITERAL
hidden_type:
hidden_importsym
Since the language construct that triggers the failure is fairly uncommon,
this is probably not urgent.
Attachments: