diff --git a/ui/build/config.go b/ui/build/config.go
index 6de7a05..0b93b18 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -33,7 +33,8 @@
 type Config struct{ *configImpl }
 
 type configImpl struct {
-	// From the environment
+	// Some targets that are implemented in soong_build
+	// (bp2build, json-module-graph) are not here and have their own bits below.
 	arguments     []string
 	goma          bool
 	environ       *Environment
@@ -41,17 +42,19 @@
 	buildDateTime string
 
 	// From the arguments
-	parallel       int
-	keepGoing      int
-	verbose        bool
-	checkbuild     bool
-	dist           bool
-	skipConfig     bool
-	skipKati       bool
-	skipKatiNinja  bool
-	skipSoong      bool
-	skipNinja      bool
-	skipSoongTests bool
+	parallel        int
+	keepGoing       int
+	verbose         bool
+	checkbuild      bool
+	dist            bool
+	jsonModuleGraph bool
+	bp2build        bool
+	skipConfig      bool
+	skipKati        bool
+	skipKatiNinja   bool
+	skipSoong       bool
+	skipNinja       bool
+	skipSoongTests  bool
 
 	// From the product config
 	katiArgs        []string
@@ -109,9 +112,6 @@
 	// Only generate build files (in a subdirectory of the out directory) and exit.
 	generateBuildFiles
 
-	// Only generate the Soong json module graph for use with jq, and exit.
-	generateJsonModuleGraph
-
 	// 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
@@ -639,6 +639,10 @@
 			c.environ.Set(k, v)
 		} else if arg == "dist" {
 			c.dist = true
+		} else if arg == "json-module-graph" {
+			c.jsonModuleGraph = true
+		} else if arg == "bp2build" {
+			c.bp2build = true
 		} else {
 			if arg == "checkbuild" {
 				c.checkbuild = true
@@ -705,6 +709,26 @@
 	return c.arguments
 }
 
+func (c *configImpl) SoongBuildInvocationNeeded() bool {
+	if c.Dist() {
+		return true
+	}
+
+	if len(c.Arguments()) > 0 {
+		// Explicit targets requested that are not special targets like b2pbuild
+		// or the JSON module graph
+		return true
+	}
+
+	if !c.JsonModuleGraph() && !c.Bp2Build() {
+		// Command line was empty, the default Ninja target is built
+		return true
+	}
+
+	// build.ninja doesn't need to be generated
+	return false
+}
+
 func (c *configImpl) OutDir() string {
 	if outDir, ok := c.environ.Get("OUT_DIR"); ok {
 		return outDir
@@ -790,6 +814,14 @@
 	return c.dist
 }
 
+func (c *configImpl) JsonModuleGraph() bool {
+	return c.jsonModuleGraph
+}
+
+func (c *configImpl) Bp2Build() bool {
+	return c.bp2build
+}
+
 func (c *configImpl) IsVerbose() bool {
 	return c.verbose
 }
@@ -935,10 +967,6 @@
 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 if c.Environment().IsEnvTrue("GENERATE_JSON_MODULE_GRAPH") {
-		return generateJsonModuleGraph
 	} else {
 		return noBazel
 	}