x/mobile: failed to compile a package with C in comments

[hajimehoshi]

What version of Go are you using (go version)?

$ go version
go version go1.12.5 darwin/amd64

$ gomobile version
gomobile version +cafc553 Mon Aug 26 17:01:11 2019 +0000 (android,ios); androidSDK=/Users/hajimehoshi/Library/Android/sdk/platforms/android-28

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/hajimehoshi/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hajimehoshi/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/ht/ky_bwgzs4bd5z1hh02k34x_h0000gn/T/go-build345783314=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Build the below file with gomobile bind -target=ios

package main

// #cgo CFLAGS: -x objective-c                                                                                                                                                                                                                
// #cgo LDFLAGS: -framework Foundation -framework UIKit                                                                                                                                                                                       
//                                                                                                                                                                                                                                            
// #import <UIKit/UIKit.h>                                                                                                                                                                                                                    
import "C"

func main() {
}

What did you expect to see?

No error related to C compilation

What did you see instead?

$ gomobile bind -target=ios .
gomobile: /Users/hajimehoshi/go/bin/gobind -lang=go,objc -outdir=/var/folders/ht/ky_bwgzs4bd5z1hh02k34x_h0000gn/T/gomobile-work-318068638 -tags=ios . failed: exit status 1
2019/08/29 23:05:27 go [list -e -json -compiled=true -test=false -export=false -deps=true -find=false -tags ios -- .]: exit status 2: # example.com
./mobile.go:6:10: fatal error: 'UIKit/UIKit.h' file not found
 #import <UIKit/UIKit.h>
         ^~~~~~~~~~~~~~~
1 error generated.

At least 597adff16ade9d88626f8caea514bb189b8c74ee worked.

[hajimehoshi]

Ah, this was duplicated with #33859

[hajimehoshi]

I found this was another case. The error message starts with # example.com (or an arbitrary package name) when C is written in a Go file.

@matloob , any thoughts?

[matloob]

Ugh, I think the best we can do is let through any errors that start with "# \n"

the compiler can spit out arbitrary error messages and trying to parse them is hopeless

[hajimehoshi]

Thanks,

Ugh, I think the best we can do is let through any errors that start with "# \n"

This would highly likely include other messages than cgo, right?

[matloob]

Unfortunately yes, but I think this is the best we can do. Long term, we need to fix go list -e to not print these errors to stderr.

[gopherbot]

Change https://golang.org/cl/192330 mentions this issue: go/packages: ignore any go list errors that seem to come from cgo

[gopherbot]

Change https://golang.org/cl/194497 mentions this issue: all: update go.mod