Subsume INTEGRATED_BP2BUILD into other env modes

This refactors bazel-build mode determination logic in soong_ui so it's
clearer which of three possible modes are being used in a given
invocation (NO_BAZEL, GENERATE_BUILD_FILES, or MIXED_BUILDS).

Test: bootstrap tests
Change-Id: I41d2baebf8d560c2cc42db8daa8b936101d453e3
diff --git a/ui/build/build.go b/ui/build/build.go
index 3692f4f..c2ad057 100644
--- a/ui/build/build.go
+++ b/ui/build/build.go
@@ -258,8 +258,8 @@
 		// Run Soong
 		runSoong(ctx, config)
 
-		if config.Environment().IsEnvTrue("GENERATE_BAZEL_FILES") {
-			// Return early, if we're using Soong as the bp2build converter.
+		if config.bazelBuildMode() == generateBuildFiles {
+			// Return early, if we're using Soong as solely the generator of BUILD files.
 			return
 		}
 	}
diff --git a/ui/build/config.go b/ui/build/config.go
index 4816d1f..1d1f71f 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -93,6 +93,21 @@
 	BUILD_MODULES
 )
 
+type bazelBuildMode int
+
+// Bazel-related build modes.
+const (
+	// Don't use bazel at all.
+	noBazel bazelBuildMode = iota
+
+	// Only generate build files (in a subdirectory of the out directory) and exit.
+	generateBuildFiles
+
+	// Generate synthetic build files and incorporate these files into a build which
+	// partially uses Bazel. Build metadata may come from Android.bp or BUILD files.
+	mixedBuild
+)
+
 // checkTopDir validates that the current directory is at the root directory of the source tree.
 func checkTopDir(ctx Context) {
 	if _, err := os.Stat(srcDirFileCheck); err != nil {
@@ -897,6 +912,16 @@
 	return c.useBazel
 }
 
+func (c *configImpl) bazelBuildMode() bazelBuildMode {
+	if c.Environment().IsEnvTrue("USE_BAZEL_ANALYSIS") {
+		return mixedBuild
+	} else if c.Environment().IsEnvTrue("GENERATE_BAZEL_FILES") {
+		return generateBuildFiles
+	} else {
+		return noBazel
+	}
+}
+
 func (c *configImpl) StartRBE() bool {
 	if !c.UseRBE() {
 		return false
diff --git a/ui/build/soong.go b/ui/build/soong.go
index 7e94b25..a41dbe1 100644
--- a/ui/build/soong.go
+++ b/ui/build/soong.go
@@ -206,7 +206,8 @@
 		}
 	}
 
-	integratedBp2Build := config.Environment().IsEnvTrue("INTEGRATED_BP2BUILD")
+	buildMode := config.bazelBuildMode()
+	integratedBp2Build := (buildMode == mixedBuild) || (buildMode == generateBuildFiles)
 
 	// This is done unconditionally, but does not take a measurable amount of time
 	bootstrapBlueprint(ctx, config, integratedBp2Build)
@@ -312,7 +313,7 @@
 
 func shouldCollectBuildSoongMetrics(config Config) bool {
 	// Do not collect metrics protobuf if the soong_build binary ran as the bp2build converter.
-	return config.Environment().IsFalse("GENERATE_BAZEL_FILES")
+	return config.bazelBuildMode() != generateBuildFiles
 }
 
 func loadSoongBuildMetrics(ctx Context, config Config) *soong_metrics_proto.SoongBuildMetrics {