Add dependency on dexpreopt.config to soong_build doc generation.

This was caught while running the soong_build docs action under Bazel as
ninja executor. Since the config file is not an explicit input to the
action, it's not present in Bazel's execution root during action
execution time, leading to a missing file error. To fix it, add the file
as an input to the action, if it's configured in product variables.

New soong_build statement:

build out/soong/docs/soong_build.html: s.writedocs.soongDocs $
        out/.module_paths/Android.bp.list out/soong/soong.variables $
        out/soong/dexpreopt.config | out/soong/.bootstrap/bin/soong_build
    outDir = out/soong/docs

Test: m
Test: USE_BAZEL=1 m
Bug: 161958189
Fixes: 161958189
Change-Id: I2bf264e848bb29ac91f4196fbe9c4ecf3cea8a2c

android/config.go

@@ -974,13 +974,21 @@ func (c *config) ModulesLoadedByPrivilegedModules() []string {
 	return c.productVariables.ModulesLoadedByPrivilegedModules
 }
 
-func (c *config) DexpreoptGlobalConfig(ctx PathContext) ([]byte, error) {
+func (c *config) DexpreoptGlobalConfigPath(ctx PathContext) OptionalPath {
 	if c.productVariables.DexpreoptGlobalConfig == nil {
+		return OptionalPathForPath(nil)
+	}
+	return OptionalPathForPath(
+		pathForBuildToolDep(ctx, *c.productVariables.DexpreoptGlobalConfig))
+}
+
+func (c *config) DexpreoptGlobalConfig(ctx PathContext) ([]byte, error) {
+	path := c.DexpreoptGlobalConfigPath(ctx)
+	if !path.Valid() {
 		return nil, nil
 	}
-	path := absolutePath(*c.productVariables.DexpreoptGlobalConfig)
-	ctx.AddNinjaFileDeps(path)
-	return ioutil.ReadFile(path)
+	ctx.AddNinjaFileDeps(path.String())
+	return ioutil.ReadFile(absolutePath(path.String()))
 }
 
 func (c *config) FrameworksBaseDirExists(ctx PathContext) bool {

android/writedocs.go

@@ -48,6 +48,13 @@ func (c *docsSingleton) GenerateBuildActions(ctx SingletonContext) {
 	deps = append(deps, pathForBuildToolDep(ctx, ctx.Config().moduleListFile))
 	deps = append(deps, pathForBuildToolDep(ctx, ctx.Config().ProductVariablesFileName))
 
+	// The dexpreopt configuration may not exist, but if it does, it's a dependency
+	// of soong_build.
+	dexpreoptConfigPath := ctx.Config().DexpreoptGlobalConfigPath(ctx)
+	if dexpreoptConfigPath.Valid() {
+		deps = append(deps, dexpreoptConfigPath.Path())
+	}
+
 	// Generate build system docs for the primary builder.  Generating docs reads the source
 	// files used to build the primary builder, but that dependency will be picked up through
 	// the dependency on the primary builder itself.  There are no dependencies on the

ui/build/test_build.go

@@ -68,6 +68,12 @@ func testForDanglingRules(ctx Context, config Config) {
 	miniBootstrapDir := filepath.Join(outDir, "soong", ".minibootstrap")
 	modulePathsDir := filepath.Join(outDir, ".module_paths")
 	variablesFilePath := filepath.Join(outDir, "soong", "soong.variables")
+	// dexpreopt.config is an input to the soong_docs action, which runs the
+	// soong_build primary builder. However, this file is created from $(shell)
+	// invocation at Kati parse time, so it's not an explicit output of any
+	// Ninja action, but it is present during the build itself and can be
+	// treated as an source file.
+	dexpreoptConfigFilePath := filepath.Join(outDir, "soong", "dexpreopt.config")
 
 	danglingRules := make(map[string]bool)
 
@@ -81,7 +87,8 @@ func testForDanglingRules(ctx Context, config Config) {
 		if strings.HasPrefix(line, bootstrapDir) ||
 			strings.HasPrefix(line, miniBootstrapDir) ||
 			strings.HasPrefix(line, modulePathsDir) ||
-			line == variablesFilePath {
+			line == variablesFilePath ||
+			line == dexpreoptConfigFilePath {
 			// Leaf node is in one of Soong's bootstrap directories, which do not have
 			// full build rules in the primary build.ninja file.
 			continue