Bug 1540820 - Don't write generated JNI wrappers for every Java-level change. r=agi

This was fallout from Bug 1509572, which moved the "invalidation
smarts" to Gradle. Unfortunately, those smarts are not smart enough:
there are many situations where the annotations might change (a new
method) but where they don't actually change (a new method that isn't
annotated with @JNITarget).

Since we don't want to spend the time to make the "invalidation
smarts" truly smart, we need to bring back this little bit of Bug
1509572.

While we're here, we ensure that there is only one JNI wrapper
generation task for GeckoView and Fennec, regardless of variant.
Right now, those are named like:

- geckoview:generateJNIWrappersForGeneratedWithGeckoBinariesDebug
- app:generateJNIWrappersForFennecWithoutGeckoBinariesDebug

See https://bugzilla.mozilla.org/show_bug.cgi?id=1509539#c1 for some
discussion of these JNI wrapper generation tasks.

Differential Revision: https://phabricator.services.mozilla.com/D26427

--HG--
extra : moz-landing-system : lando

Author: ncalexan

mobile/android/annotations/src/main/java/org/mozilla/gecko/annotationProcessors/AnnotationProcessor.java

@@ -170,6 +170,21 @@ private static String getHeaderGuardName(final String name) {
     private static int writeOutputFile(final String name, final StringBuilder content) {
         final byte[] contentBytes = content.toString().getBytes(StandardCharsets.UTF_8);
 
+        try {
+            final byte[] existingBytes = Files.readAllBytes(new File(name).toPath());
+            if (Arrays.equals(contentBytes, existingBytes)) {
+                return 0;
+            }
+        } catch (FileNotFoundException e) {
+            // Pass.
+        } catch (NoSuchFileException e) {
+            // Pass.
+        } catch (IOException e) {
+            System.err.println("Unable to read " + name + ". Perhaps a permissions issue?");
+            e.printStackTrace(System.err);
+            return 1;
+        }
+
         try (FileOutputStream outStream = new FileOutputStream(name)) {
             outStream.write(contentBytes);
         } catch (IOException e) {

mobile/android/app/build.gradle

@@ -382,7 +382,9 @@ android.applicationVariants.all { variant ->
 }
 
 android.applicationVariants.all { variant ->
-    configureApplicationVariantWithJNIWrappers(variant, "Fennec")
+    if (variant.name == mozconfig.substs.GRADLE_ANDROID_APP_VARIANT_NAME) {
+        configureApplicationVariantWithJNIWrappers(variant, "Fennec")
+    }
 }
 
 if (gradle.startParameter.taskNames.any { it.endsWith('UnitTest') }) {

mobile/android/geckoview/build.gradle

@@ -309,7 +309,9 @@ android.libraryVariants.all { variant ->
 }
 
 android.libraryVariants.all { variant ->
-    configureLibraryVariantWithJNIWrappers(variant, "Generated")
+    if (variant.name == mozconfig.substs.GRADLE_ANDROID_GECKOVIEW_VARIANT_NAME) {
+        configureLibraryVariantWithJNIWrappers(variant, "Generated")
+    }
 }
 
 apply plugin: 'maven-publish'