proposal: cmd/cgo: pkg-config support default pc file

[chai2010]

cgo user can custom default pc file to change CFLAGS and LDFLAGS.

for example:

#cgo pkg-config png

will read ${GOPATH}/pkg/cgo_${GOOS}_${GOARCH}/png.pc at first (donot need install ‘pkg-config’ tool):

# See: man pkg-config
pkgroot=${GOPATH}/pkg/cgo_${GOOS}_${GOARCH}/png

Name: png
Description: png library
Version: 1.2.3

Requires:
Cflags: -I${pkgroot}/include
Libs: -L${pkgroot}/lib -lpng

if no default pc file, then use local pkg-config tool.

[ianlancetaylor]

It seems to me that we can already do this using #cgo comments. What is the advantage to putting those flags into a .pc file?

[chai2010]

@ianlancetaylor
as cgo user, i hope use different cflags and ldflags for dev and release mode (build target and zip).
if use #cgo comments, i need change the code.
if use .pc file, i can set PKG_CONFIG_PATH to custom pc file for release mode.

[rsc]

GOPATH/pkg is really meant for binaries and things that can be regenerated.
It is a bit surprising to put a directory of configuration files into GOPATH/pkg/cgo_GOOS_GOARCH/

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[rsc]

Based on the discussion above, this proposal seems like a likely decline.
— rsc for the proposal review group

[rsc]

No change in consensus, so declined.
— rsc for the proposal review group