Make running soong_build in alternate modes nicer.

This includes the JSON graph generator and bp2build.

Before:
GENERATE_BAZEL_FILES=1 m nothing
GENERATE_JSON_MODULE_GRAPH=1 m nothing

Now:
m json-module-graph
m bp2build

They can now also be combined with other targets or each other.

The longer-term goal is to run "m queryview" and "m soong_docs" using
the same infrastructure. There are two alternate approaches:

1. Call soong_build from within the main Ninja invocation. This requires
two sequential soong_build invocations and is thus slower.
2. Do everything requested in the same soong_build invocation. This
would be faster, but one AFAIU can't tell Ninja that multiple possible
actions can build the same output so that doesn't work.

(1) is somewhat more desirable because soong_docs seems to be built
from build/make/core/main.mk ; I assume that that can be worked around
although I haven't checked where the output of "m soong_docs" goes.

Test: Presubmits.
Change-Id: If5ba36490d9f3f60733e6d6be9286eb2b67c3ff5

ui/build/config.go

@@ -33,7 +33,8 @@ import (
 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 @@ type configImpl struct {
 	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 @@ const (
 	// 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 @@ func (c *configImpl) parseArgs(ctx Context, args []string) {
 			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 @@ func (c *configImpl) Arguments() []string {
 	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 @@ func (c *configImpl) Dist() bool {
 	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) UseBazel() bool {
 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
 	}