Validate monolithic and modular hidden API flags are consistent

This makes sure that where there is overlap between the hidden API
flags generated for a module and the monolithic flags that they are
identical. That ensures that the modular hidden API flags will be
compatible with previous releases that relied on the monolithic flags.

Bug: 179354495
Test: m out/soong/.intermediates/art/build/boot/art-bootclasspath-fragment/android_common_apex10000/modular-hiddenapi/all-flags.csv
      m out/soong/hiddenapi/hiddenapi-flags.csv
      - Create some inconsistencies between the above two files.
      m out/soong/hiddenapi/hiddenapi-flags.csv.valid
Change-Id: Iaf9e23cef63e221608955d89dc8d496bcc70c86e

java/hiddenapi_modular.go

@@ -15,6 +15,8 @@
 package java
 
 import (
+	"strings"
+
 	"android/soong/android"
 	"github.com/google/blueprint"
 )
@@ -378,6 +380,16 @@ func (i *hiddenAPIFlagFileInfo) append(other hiddenAPIFlagFileInfo) {
 
 var hiddenAPIFlagFileInfoProvider = blueprint.NewProvider(hiddenAPIFlagFileInfo{})
 
+// pathForValidation creates a path of the same type as the supplied type but with a name of
+// <path>.valid.
+//
+// e.g. If path is an OutputPath for out/soong/hiddenapi/hiddenapi-flags.csv then this will return
+// an OutputPath for out/soong/hiddenapi/hiddenapi-flags.csv.valid
+func pathForValidation(ctx android.PathContext, path android.WritablePath) android.WritablePath {
+	extWithoutLeadingDot := strings.TrimPrefix(path.Ext(), ".")
+	return path.ReplaceExtension(ctx, extWithoutLeadingDot+".valid")
+}
+
 // buildRuleToGenerateHiddenApiFlags creates a rule to create the monolithic hidden API flags from
 // the flags from all the modules, the stub flags, augmented with some additional configuration
 // files.
@@ -392,6 +404,30 @@ var hiddenAPIFlagFileInfoProvider = blueprint.NewProvider(hiddenAPIFlagFileInfo{
 // augmentationInfo is a struct containing paths to files that augment the information provided by
 // the moduleSpecificFlagsPaths.
 func buildRuleToGenerateHiddenApiFlags(ctx android.BuilderContext, name, desc string, outputPath android.WritablePath, baseFlagsPath android.Path, moduleSpecificFlagsPaths android.Paths, flagFileInfo *hiddenAPIFlagFileInfo) {
+
+	// The file which is used to record that the flags file is valid.
+	var validFile android.WritablePath
+
+	// If there are flag files that have been generated by fragments on which this depends then use
+	// them to validate the flag file generated by the rules created by this method.
+	if allFlagsPaths := flagFileInfo.AllFlagsPaths; len(allFlagsPaths) > 0 {
+		// The flags file generated by the rule created by this method needs to be validated to ensure
+		// that it is consistent with the flag files generated by the individual fragments.
+
+		validFile = pathForValidation(ctx, outputPath)
+
+		// Create a rule to validate the output from the following rule.
+		rule := android.NewRuleBuilder(pctx, ctx)
+		rule.Command().
+			BuiltTool("verify_overlaps").
+			Input(outputPath).
+			Inputs(allFlagsPaths).
+			// If validation passes then update the file that records that.
+			Text("&& touch").Output(validFile)
+		rule.Build(name+"Validation", desc+" validation")
+	}
+
+	// Create the rule that will generate the flag files.
 	tempPath := tempPathForRestat(ctx, outputPath)
 	rule := android.NewRuleBuilder(pctx, ctx)
 	command := rule.Command().
@@ -410,6 +446,14 @@ func buildRuleToGenerateHiddenApiFlags(ctx android.BuilderContext, name, desc st
 
 	commitChangeForRestat(rule, tempPath, outputPath)
 
+	if validFile != nil {
+		// Add the file that indicates that the file generated by this is valid.
+		//
+		// This will cause the validation rule above to be run any time that the output of this rule
+		// changes but the validation will run in parallel with other rules that depend on this file.
+		command.Validation(validFile)
+	}
+
 	rule.Build(name, desc)
 }