code review 150360043: cmd/cc, runtime: disallow structs without tags

cmd/cc, runtime: disallow structs without tags

Structs without tags have no unique name to use in the
Go definitions generated from the C types.
This caused issue 8812, fixed by CL 149260043.
Avoid future problems by requiring struct tags.

Update runtime as needed.
(There is no other C code in the tree.)

[rsc, 2014-10-01 00:50:43]

Hello golang-codereviews@googlegroups.com (cc: dfc, iant, khr, r),

I'd like you to review this change to
https://code.google.com/p/go/

[bradfitz, 2014-10-01 00:56:53]

LGTM

[dave_cheney.net, 2014-10-01 00:59:43]

Thanks Russ.

https://codereview.appspot.com/150360043/diff/40001/src/cmd/cc/cc.y
File src/cmd/cc/cc.y (right):

https://codereview.appspot.com/150360043/diff/40001/src/cmd/cc/cc.y#newcode1046
src/cmd/cc/cc.y:1046: diag(Z, "tagless struct");
nit: i know this is only an internal error for runtime developers, but maybe
this would be a better error 

"untagged struct; tagged structs are required for precise GC"

https://codereview.appspot.com/150360043/diff/40001/src/runtime/os_plan9.h
File src/runtime/os_plan9.h (right):

https://codereview.appspot.com/150360043/diff/40001/src/runtime/os_plan9.h#ne...
src/runtime/os_plan9.h:66: struct TosProf			/* Per process profiling */
nit: one too many \t 's

[iant, 2014-10-01 01:11:23]

LGTM

[rsc, 2014-10-03 16:44:24]

*** Submitted as https://code.google.com/p/go/source/detail?r=6f838e507399 ***

cmd/cc, runtime: disallow structs without tags

Structs without tags have no unique name to use in the
Go definitions generated from the C types.
This caused issue 8812, fixed by CL 149260043.
Avoid future problems by requiring struct tags.

Update runtime as needed.
(There is no other C code in the tree.)

LGTM=bradfitz, iant
R=golang-codereviews, bradfitz, dave, iant
CC=golang-codereviews, khr, r
https://codereview.appspot.com/150360043

https://codereview.appspot.com/150360043/diff/40001/src/cmd/cc/cc.y
File src/cmd/cc/cc.y (right):

https://codereview.appspot.com/150360043/diff/40001/src/cmd/cc/cc.y#newcode1046
src/cmd/cc/cc.y:1046: diag(Z, "tagless struct");
On 2014/10/01 00:59:43, dfc wrote:
> nit: i know this is only an internal error for runtime developers, but maybe
> this would be a better error 
> 
> "untagged struct; tagged structs are required for precise GC"

Such a detailed, verbose error would be clearly out of place in this code base.
It's all going away very soon.

I did change it to 'struct must have tag' so that it says what's wrong instead
of just stating a fact and leaving the incorrectness to be inferred.