Match Rust gcda output to cc via -Z profile-emit.

Use the -Z profile-emit flag to ensure that rust gcda files have
/proc/self/cwd/ appended to them similar to cc modules. This makes sure
our gcda output is consistent no matter what language the binary is
written in.

Bug: 156482307
Test: gcda outputs to the new path.

Change-Id: Ife4d55f885c7e33dffa66f7436bc2bf8b5916586

cc/builder.go

@@ -283,16 +283,19 @@ var (
 		"cFlags")
 )
 
+func PwdPrefix() string {
+	// Darwin doesn't have /proc
+	if runtime.GOOS != "darwin" {
+		return "PWD=/proc/self/cwd"
+	}
+	return ""
+}
+
 func init() {
 	// We run gcc/clang with PWD=/proc/self/cwd to remove $TOP from the
 	// debug output. That way two builds in two different directories will
 	// create the same output.
-	if runtime.GOOS != "darwin" {
-		pctx.StaticVariable("relPwd", "PWD=/proc/self/cwd")
-	} else {
-		// Darwin doesn't have /proc
-		pctx.StaticVariable("relPwd", "")
-	}
+	pctx.StaticVariable("relPwd", PwdPrefix())
 
 	pctx.HostBinToolVariable("SoongZipCmd", "soong_zip")
 	pctx.Import("android/soong/remoteexec")

rust/builder.go

@@ -21,6 +21,7 @@ import (
 	"github.com/google/blueprint/pathtools"
 
 	"android/soong/android"
+	"android/soong/cc"
 )
 
 var (
@@ -161,11 +162,17 @@ func transformSrctoCrate(ctx android.ModuleContext, main android.Path, deps Path
 
 	if flags.Coverage {
 		var gcnoFile android.WritablePath
+		// Provide consistency with cc gcda output, see cc/builder.go init()
+		profileEmitArg := strings.TrimPrefix("PWD=", cc.PwdPrefix()) + "/"
 
 		if outputFile.Ext() != "" {
 			gcnoFile = android.PathForModuleOut(ctx, pathtools.ReplaceExtension(outputFile.Base(), "gcno"))
+			rustcFlags = append(rustcFlags, "-Z profile-emit="+profileEmitArg+android.PathForModuleOut(
+				ctx, pathtools.ReplaceExtension(outputFile.Base(), "gcda")).String())
 		} else {
 			gcnoFile = android.PathForModuleOut(ctx, outputFile.Base()+".gcno")
+			rustcFlags = append(rustcFlags, "-Z profile-emit="+profileEmitArg+android.PathForModuleOut(
+				ctx, outputFile.Base()+".gcda").String())
 		}
 
 		implicitOutputs = append(implicitOutputs, gcnoFile)