Deprecate USE_GOMA and replace with FORCE_USE_GOMA

Bug: b/163361527
Test: Ran builds with USE_GOMA / FORCE_USE_GOMA flags
Change-Id: I67b229fbf52e913b0c4f5e7932021132ddc0598f
diff --git a/ui/build/config.go b/ui/build/config.go
index e9a8fc9..9bd0877 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -24,6 +24,7 @@
 	"time"
 
 	"android/soong/shared"
+
 	"github.com/golang/protobuf/proto"
 
 	smpb "android/soong/ui/metrics/metrics_proto"
@@ -183,6 +184,17 @@
 		"EMPTY_NINJA_FILE",
 	)
 
+	if ret.UseGoma() {
+		ctx.Println("Goma for Android is being deprecated and replaced with RBE. See go/rbe_for_android for instructions on how to use RBE.")
+		ctx.Println()
+		ctx.Println("See go/goma_android_exceptions for exceptions.")
+		ctx.Fatalln("USE_GOMA flag is no longer supported.")
+	}
+
+	if ret.ForceUseGoma() {
+		ret.environ.Set("USE_GOMA", "true")
+	}
+
 	// Tell python not to spam the source tree with .pyc files.
 	ret.environ.Set("PYTHONDONTWRITEBYTECODE", "1")
 
@@ -778,6 +790,18 @@
 	return c.totalRAM
 }
 
+// ForceUseGoma determines whether we should override Goma deprecation
+// and use Goma for the current build or not.
+func (c *configImpl) ForceUseGoma() bool {
+	if v, ok := c.environ.Get("FORCE_USE_GOMA"); ok {
+		v = strings.TrimSpace(v)
+		if v != "" && v != "false" {
+			return true
+		}
+	}
+	return false
+}
+
 func (c *configImpl) UseGoma() bool {
 	if v, ok := c.environ.Get("USE_GOMA"); ok {
 		v = strings.TrimSpace(v)