x/mobile/cmd/gomobile: CGO_CFLAGS is overwritten during go bind -target=ios

[hsinhoyeh]

hi,
I faced an issue when I run gomobile bind with CGO_CFLAGS and CGO_LDFLAGS like

CGO_CFLAGS="-I/usr/local/include" \
CGO_LDFLAGS="-L/usr/local/lib" gomobile build -target=ios -v

but output told me that there a header file not found.
It turns out when we build ios, the CGO_CFLAGS and CGO_LDFLAGS are overwritten.
https://github.com/golang/mobile/blob/master/cmd/gomobile/env.go#L132

I have a way to workaround this:

index 5458bc2..00cb78c 100644
--- a/cmd/gomobile/env.go
+++ b/cmd/gomobile/env.go
@@ -119,8 +119,8 @@ func envInit() (err error) {
                "GOARM=7",
                "CC=" + clang,
                "CXX=" + clang,
-               "CGO_CFLAGS=" + cflags + " -arch " + archClang("arm"),
-               "CGO_LDFLAGS=" + cflags + " -arch " + archClang("arm"),
+               "CGO_CFLAGS=" + os.Getenv("CGO_CFLAGS") + " " + cflags + " -arch " + archClang("arm"),
+               "CGO_LDFLAGS=" + os.Getenv("CGO_LDFLAGS") + " " + cflags + " -arch " + archClang("arm"),
                "CGO_ENABLED=1",
        }
        darwinArm64Env = []string{
@@ -128,8 +128,8 @@ func envInit() (err error) {
                "GOARCH=arm64",
                "CC=" + clang,
                "CXX=" + clang,
-               "CGO_CFLAGS=" + cflags + " -arch " + archClang("arm64"),
-               "CGO_LDFLAGS=" + cflags + " -arch " + archClang("arm64"),
+               "CGO_CFLAGS=" + os.Getenv("CGO_CFLAGS") + " " + cflags + " -arch " + archClang("arm64"),
+               "CGO_LDFLAGS=" + os.Getenv("CGO_LDFLAGS") + " " + cflags + " -arch " + archClang("arm64"),
                "CGO_ENABLED=1",
        }

@@ -142,8 +142,8 @@ func envInit() (err error) {
                "GOARCH=386",
                "CC=" + clang,
                "CXX=" + clang,
-               "CGO_CFLAGS=" + cflags + " -mios-simulator-version-min=6.1 -arch " + archClang("386"),
-               "CGO_LDFLAGS=" + cflags + " -mios-simulator-version-min=6.1 -arch " + archClang("386"),
+               "CGO_CFLAGS=" + os.Getenv("CGO_CFLAGS") + " " + cflags + " -mios-simulator-version-min=6.1 -arch " + archClang("386"),
+               "CGO_LDFLAGS=" + os.Getenv("CGO_LDFLAGS") + " " + cflags + " -mios-simulator-version-min=6.1 -arch " + archClang("386"),
                "CGO_ENABLED=1",
        }
        darwinAmd64Env = []string{

let me know if you think this is an issue.

[crawshaw]

It would be nice to be able to set these flags when using gomobile. It's an odd middle-ground however: we deliberately ignore some variables like GOOS, GOARCH, CC, and CXX, but we will use the flags variables? And we will apply the same CC flags to different compilers?

[hsinhoyeh]

I think it is better to have a flag variable to determine whether we want to inherit CFO_CFLAGS and CGO_LDFLAGS from env. It should be caller's call to deal with different compilers.
how do you think?

[eliasnaur]

With https://go-review.googlesource.com/99316 in it is now possible to generate complete bindings with the gobind tool, skip gomobile and build the JNI lbraries manually with CC=... CXX=... CGO_ENABLED=1 GOOS=android GOARCH=... go build -buildmode=c-shared.
(With pending https://go-review.googlesource.com/c/mobile/+/99875 gomobile will change to use standalone toolchains, and build exactly as above)
Does that solution help you?