[backport] chore(buildtool): add ios-build unit tests

This diff backports #1371 to the release/3.19 branch.

We needed to move the runtimex.Assert for darwin, otherwise we cannot
run unit tests on linux 😅. While there, be consistent and make sure we
avoid panicking on Windows if one runs unit tests there.

Part of ooni/probe#2564

internal/cmd/buildtool/android.go

@@ -31,6 +31,12 @@ func androidSubcommand() *cobra.Command {
 		Use:   "gomobile",
 		Short: "Builds oonimkall for android using gomobile",
 		Run: func(cmd *cobra.Command, args []string) {
+			// Implementation note: perform the check here such that we can
+			// run unit test for the building code from any system
+			runtimex.Assert(
+				runtime.GOOS == "darwin" || runtime.GOOS == "linux",
+				"this command requires darwin or linux",
+			)
 			androidBuildGomobile(&buildDeps{})
 		},
 	})
@@ -39,6 +45,12 @@ func androidSubcommand() *cobra.Command {
 		Use:   "cli",
 		Short: "Builds ooniprobe and miniooni for usage within termux",
 		Run: func(cmd *cobra.Command, args []string) {
+			// Implementation note: perform the check here such that we can
+			// run unit test for the building code from any system
+			runtimex.Assert(
+				runtime.GOOS == "darwin" || runtime.GOOS == "linux",
+				"this command requires darwin or linux",
+			)
 			androidBuildCLIAll(&buildDeps{})
 		},
 	})
@@ -48,6 +60,12 @@ func androidSubcommand() *cobra.Command {
 		Short: "Cross compiles C dependencies for Android",
 		Run: func(cmd *cobra.Command, args []string) {
 			for _, arg := range args {
+				// Implementation note: perform the check here such that we can
+				// run unit test for the building code from any system
+				runtimex.Assert(
+					runtime.GOOS == "darwin" || runtime.GOOS == "linux",
+					"this command requires darwin or linux",
+				)
 				androidCdepsBuildMain(arg, &buildDeps{})
 			}
 		},
@@ -59,11 +77,6 @@ func androidSubcommand() *cobra.Command {
 
 // androidBuildGomobile invokes the gomobile build.
 func androidBuildGomobile(deps buildtoolmodel.Dependencies) {
-	runtimex.Assert(
-		runtime.GOOS == "darwin" || runtime.GOOS == "linux",
-		"this command requires darwin or linux",
-	)
-
 	deps.PsiphonMaybeCopyConfigFiles()
 	deps.GolangCheck()
 
@@ -132,11 +145,6 @@ func androidNDKCheck(androidHome string) string {
 
 // androidBuildCLIAll builds all products in CLI mode for Android
 func androidBuildCLIAll(deps buildtoolmodel.Dependencies) {
-	runtimex.Assert(
-		runtime.GOOS == "darwin" || runtime.GOOS == "linux",
-		"this command requires darwin or linux",
-	)
-
 	deps.PsiphonMaybeCopyConfigFiles()
 	deps.GolangCheck()
 
@@ -379,10 +387,6 @@ func androidNDKBinPath(ndkDir string) string {
 
 // androidCdepsBuildMain builds C dependencies for android.
 func androidCdepsBuildMain(name string, deps buildtoolmodel.Dependencies) {
-	runtimex.Assert(
-		runtime.GOOS == "darwin" || runtime.GOOS == "linux",
-		"this command requires darwin or linux",
-	)
 	androidHome := deps.AndroidSDKCheck()
 	ndkDir := deps.AndroidNDKCheck(androidHome)
 	archs := []string{"arm", "arm64", "386", "amd64"}

internal/cmd/buildtool/internal/buildtooltest/buildtooltest.go

@@ -85,7 +85,7 @@ func CheckSingleCommand(cmd *execabs.Cmd, tee ExecExpectations) error {
 		return err
 	}
 	if err := CompareEnv(tee.Env, shellxtesting.CmdEnvironMinusOsEnviron(cmd)); err != nil {
-		return err
+		return fmt.Errorf("in %v: %w", tee.Argv, err)
 	}
 	return nil
 }
@@ -253,12 +253,12 @@ func (*DependenciesCallCounter) XCRun(args ...string) string {
 	case "-sdk":
 		runtimex.Assert(len(args) == 3, "expected three arguments")
 		runtimex.Assert(args[2] == "--show-sdk-path", "the third argument must be --show-sdk-path")
-		return filepath.Join("Developer", "SDKs", args[1])
+		return string(filepath.Separator) + filepath.Join("Developer", "SDKs", args[1])
 
 	case "-find":
 		runtimex.Assert(len(args) == 4, "expected four arguments")
 		runtimex.Assert(args[1] == "-sdk", "the second argument must be -sdk")
-		return filepath.Join("Developer", "SDKs", args[2], "bin", args[3])
+		return string(filepath.Separator) + filepath.Join("Developer", "SDKs", args[2], "bin", args[3])
 
 	default:
 		panic(errors.New("the first argument must be -sdk or -find"))

internal/cmd/buildtool/ios.go

@@ -37,6 +37,9 @@ func iosSubcommand() *cobra.Command {
 		Use:   "cdeps [zlib|openssl|libevent|tor...]",
 		Short: "Cross compiles C dependencies for iOS",
 		Run: func(cmd *cobra.Command, args []string) {
+			// Implementation note: perform the check here such that we can
+			// run unit test for the building code from any system
+			runtimex.Assert(runtime.GOOS == "darwin", "this command requires darwin")
 			for _, arg := range args {
 				iosCdepsBuildMain(arg, &buildDeps{})
 			}
@@ -66,8 +69,6 @@ func iosBuildGomobile(deps buildtoolmodel.Dependencies) {
 
 // iosCdepsBuildMain builds C dependencies for ios.
 func iosCdepsBuildMain(name string, deps buildtoolmodel.Dependencies) {
-	runtimex.Assert(runtime.GOOS == "darwin", "this command requires darwin")
-
 	// The ooni/probe-ios app explicitly only targets amd64 and arm64. It also targets
 	// as the minimum version iOS 12, while one cannot target a version of iOS > 10 when
 	// building for 32-bit targets. Hence, using only 64 bit archs here is fine.
@@ -150,9 +151,9 @@ func iosNewCBuildEnv(deps buildtoolmodel.Dependencies, ooniArch string) *cBuildE
 		CFLAGS: []string{
 			"-isysroot", isysroot,
 			minVersionFlag + iosMinVersion, // tricky: they must be concatenated
-			"-O2",
 			"-arch", appleArch,
 			"-fembed-bitcode",
+			"-O2",
 		},
 		CONFIGURE_HOST: "", // later
 		DESTDIR:        destdir,