gomobile: init at 2020-06-22

The Android SDK is provided by `nixpkgs`, and in case of the Status Project
we build our app using that SDK in combination with gomobile since our
protocol library is written in Go:
https://github.com/golang/mobile

This tool is quite powerful and allows you even to build entire applications in Go:
https://pkg.go.dev/golang.org/x/mobile/cmd/gomobile#hdr-Compile_android_APK_and_iOS_app

Signed-off-by: Jakub Sokołowski <jakub@status.im>

pkgs/development/mobile/gomobile/default.nix

@@ -0,0 +1,61 @@
+{ stdenv, lib, fetchgit, buildGoModule, zlib, makeWrapper, xcodeenv, androidenv
+, xcodeWrapperArgs ? { }
+, xcodeWrapper ? xcodeenv.composeXcodeWrapper xcodeWrapperArgs
+, androidPkgs ? androidenv.composeAndroidPackages {
+    includeNDK = true;
+    ndkVersion = "21.3.6528147"; # WARNING: 22.0.7026061 is broken.
+  } }:
+
+buildGoModule {
+  pname = "gomobile";
+  version = "unstable-2020-06-22";
+
+  vendorSha256 = "1n1338vqkc1n8cy94501n7jn3qbr28q9d9zxnq2b4rxsqjfc9l94";
+
+  src = fetchgit {
+    # WARNING: Next commit removes support for ARM 32 bit builds for iOS
+    rev = "33b80540585f2b31e503da24d6b2a02de3c53ff5";
+    name = "gomobile";
+    url = "https://go.googlesource.com/mobile";
+    sha256 = "0c9map2vrv34wmaycsv71k4day3b0z5p16yzxmlp8amvqb38zwlm";
+  };
+
+  subPackages = [ "bind" "cmd/gobind" "cmd/gomobile" ];
+
+  # Fails with: go: cannot find GOROOT directory
+  doCheck = false;
+
+  patches = [ ./resolve-nix-android-sdk.patch ];
+
+  nativeBuildInputs = [ makeWrapper ]
+    ++ lib.optionals stdenv.isDarwin [ xcodeWrapper ];
+
+  # Prevent a non-deterministic temporary directory from polluting the resulting object files
+  postPatch = ''
+    substituteInPlace cmd/gomobile/env.go --replace \
+      'tmpdir, err = ioutil.TempDir("", "gomobile-work-")' \
+      'tmpdir = filepath.Join(os.Getenv("NIX_BUILD_TOP"), "gomobile-work")' \
+      --replace '"io/ioutil"' ""
+    substituteInPlace cmd/gomobile/init.go --replace \
+      'tmpdir, err = ioutil.TempDir(gomobilepath, "work-")' \
+      'tmpdir = filepath.Join(os.Getenv("NIX_BUILD_TOP"), "work")'
+  '';
+
+  # Necessary for GOPATH when using gomobile.
+  postInstall = ''
+    mkdir -p $out/src/golang.org/x
+    ln -s $src $out/src/golang.org/x/mobile
+    wrapProgram $out/bin/gomobile \
+      --prefix LD_LIBRARY_PATH : "${lib.makeLibraryPath [ zlib ]}" \
+      --prefix PATH : "${androidPkgs.androidsdk}/bin" \
+      --set ANDROID_HOME "${androidPkgs.androidsdk}/libexec/android-sdk" \
+      --set GOPATH $out
+  '';
+
+  meta = with lib; {
+    description = "A tool for building and running mobile apps written in Go";
+    homepage = "https://pkg.go.dev/golang.org/x/mobile/cmd/gomobile";
+    license = licenses.bsd3;
+    maintainers = with maintainers; [ jakubgs ];
+  };
+}

pkgs/development/mobile/gomobile/resolve-nix-android-sdk.patch

@@ -0,0 +1,15 @@
+diff --git a/cmd/gomobile/bind_androidapp.go b/cmd/gomobile/bind_androidapp.go
+index 3b01adc..76216fa 100644
+--- a/cmd/gomobile/bind_androidapp.go
++++ b/cmd/gomobile/bind_androidapp.go
+@@ -372,6 +372,10 @@ func androidAPIPath() (string, error) {
+ 	var apiVer int
+ 	for _, fi := range fis {
+ 		name := fi.Name()
++		// Resolve symlinked directories (this is how the Nix Android SDK package is built)
++		if fi2, err := os.Stat(filepath.Join(sdkDir.Name(), name)); err == nil {
++			fi = fi2
++		}
+ 		if !fi.IsDir() || !strings.HasPrefix(name, "android-") {
+ 			continue
+ 		}

pkgs/top-level/all-packages.nix

@@ -1563,6 +1563,10 @@ in
 
   xcodeenv = callPackage ../development/mobile/xcodeenv { };
 
+  gomobile = callPackage ../development/mobile/gomobile {
+    buildGoModule = buildGo115Module;
+  };
+
   ssh-agents = callPackage ../tools/networking/ssh-agents { };
 
   ssh-import-id = python3Packages.callPackage ../tools/admin/ssh-import-id { };