[Bazel] Implement namespaced R classes + avoid resource merging

Enable rudimentary R class namespacing where each library only contains
references to the resources it declares instead of declarations plus all
transitive dependency references.

This saves a total of 215MB outputs + 145 Actions for a clean build.

* No resource merging for android_library targets
* Smaller R.{class,txt}
* Less desugaring + dexing

src/main/java/com/google/devtools/build/lib/rules/android/AarImport.java

@@ -113,7 +113,8 @@ public ConfiguredTarget create(RuleContext ruleContext)
                 manifest,
                 DataBinding.contextFrom(ruleContext, dataContext.getAndroidConfig()),
                 neverlink,
-                dataContext.getAndroidConfig().linkLibraryResources());
+                dataContext.getAndroidConfig().linkLibraryResources(),
+                /* namespacedRClass = */ false);
 
     MergedAndroidAssets mergedAssets =
         AndroidAssets.forAarImport(assets)

src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java

@@ -885,6 +885,15 @@ public static class Options extends FragmentOptions {
         help = "If disabled does not run aapt2 link for android_library targets")
     public boolean linkLibraryResources;
 
+    @Option(
+        name = "namespaced_r_class",
+        defaultValue = "false",
+        documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+        effectTags = {OptionEffectTag.CHANGES_INPUTS},
+        help = "If enabled each library only contains references to the resources it declares"
+            + " instead of declarations plus all dependency references.")
+    public boolean namespacedRClass;
+
     @Option(
             name = "output_library_linked_resources",
             defaultValue = "true",
@@ -1021,6 +1030,7 @@ public ImmutableSet<Class<? extends FragmentOptions>> requiredOptions() {
   private final boolean useRTxtFromMergedResources;
   private final boolean outputLibraryMergedAssets;
   private final boolean linkLibraryResources;
+  private final boolean namespacedRClass;
   private final boolean outputLibraryLinkedResources;
   private final Label legacyMainDexListGenerator;
   private final boolean disableInstrumentationManifestMerging;
@@ -1079,6 +1089,7 @@ private AndroidConfiguration(Options options) throws InvalidConfigurationExcepti
     this.filterLibraryJarWithProgramJar = options.filterLibraryJarWithProgramJar;
     this.useRTxtFromMergedResources = options.useRTxtFromMergedResources;
     this.linkLibraryResources = options.linkLibraryResources;
+    this.namespacedRClass = options.namespacedRClass;
     this.outputLibraryLinkedResources = options.outputLibraryLinkedResources;
     this.outputLibraryMergedAssets = options.outputLibraryMergedAssets;
     this.legacyMainDexListGenerator = options.legacyMainDexListGenerator;
@@ -1345,6 +1356,10 @@ boolean linkLibraryResources() {
     return linkLibraryResources;
   }
 
+  boolean namespacedRClass() {
+    return namespacedRClass;
+  }
+
   boolean outputLibraryLinkedResources() {
     return outputLibraryLinkedResources;
   }

src/main/java/com/google/devtools/build/lib/rules/android/AndroidLibrary.java

@@ -162,7 +162,8 @@ public ConfiguredTarget create(RuleContext ruleContext)
                   manifest,
                   DataBinding.contextFrom(ruleContext, dataContext.getAndroidConfig()),
                   isNeverLink,
-                  androidConfig.linkLibraryResources());
+                  androidConfig.linkLibraryResources(),
+                  androidConfig.namespacedRClass());
 
       MergedAndroidAssets assets = AndroidAssets.from(ruleContext).process(dataContext, assetDeps);
 

src/main/java/com/google/devtools/build/lib/rules/android/AndroidResourceParsingActionBuilder.java

@@ -38,6 +38,8 @@ public class AndroidResourceParsingActionBuilder {
   // Optional outputs
   @Nullable private Artifact compiledSymbols;
   @Nullable private Artifact dataBindingInfoZip;
+  @Nullable private Artifact classJarOut;
+  @Nullable private Artifact rTxtOut;
 
   /** Set the artifact location for the output protobuf. */
   public AndroidResourceParsingActionBuilder setOutput(Artifact output) {
@@ -73,6 +75,16 @@ public AndroidResourceParsingActionBuilder setCompiledSymbolsOutput(
     return this;
   }
 
+  public AndroidResourceParsingActionBuilder setClassJarOut(Artifact classJarOut) {
+    this.classJarOut = classJarOut;
+    return this;
+  }
+
+  public AndroidResourceParsingActionBuilder setRTxtOut(Artifact rTxtOut) {
+    this.rTxtOut = rTxtOut;
+    return this;
+  }
+
   public AndroidResourceParsingActionBuilder setDataBindingInfoZip(Artifact dataBindingInfoZip) {
     this.dataBindingInfoZip = dataBindingInfoZip;
     return this;
@@ -109,7 +121,18 @@ private void build(AndroidDataContext dataContext) {
             .addOutput("--dataBindingInfoOut", dataBindingInfoZip);
       }
 
-      compiledBuilder.buildAndRegister("Compiling Android resources", "AndroidResourceCompiler");
+      if (classJarOut != null) {
+        compiledBuilder.maybeAddOutput("--classJarOutput", classJarOut);
+      }
+
+      if (rTxtOut != null) {
+        compiledBuilder.maybeAddOutput("--rTxtOut", rTxtOut);
+      }
+
+      compiledBuilder.addAndroidJar()
+          .addLabelFlag("--targetLabel")
+          .maybeAddInput("--manifest", manifest)
+          .buildAndRegister("Compiling Android resources", "AndroidResourceCompiler");
     }
   }
 
@@ -135,6 +158,8 @@ public ParsedAndroidResources build(
         androidResources,
         output,
         compiledSymbols,
+        classJarOut,
+        rTxtOut,
         dataContext.getLabel(),
         manifest,
         dataBindingContext);

src/main/java/com/google/devtools/build/lib/rules/android/AndroidResources.java

@@ -395,9 +395,11 @@ public Optional<? extends AndroidResources> maybeFilter(
   public ParsedAndroidResources parse(
       AndroidDataContext dataContext,
       StampedAndroidManifest manifest,
-      DataBindingContext dataBindingContext)
+      DataBindingContext dataBindingContext,
+      boolean generateNamespacedRFiles)
       throws InterruptedException {
-    return ParsedAndroidResources.parseFrom(dataContext, this, manifest, dataBindingContext);
+    return ParsedAndroidResources.parseFrom(dataContext, this, manifest, dataBindingContext,
+        generateNamespacedRFiles);
   }
 
   /**
@@ -410,25 +412,33 @@ public ValidatedAndroidResources process(
       StampedAndroidManifest manifest,
       DataBindingContext dataBindingContext,
       boolean neverlink,
-      boolean linkResources)
+      boolean linkResources,
+      boolean namespacedRClass)
       throws RuleErrorException, InterruptedException {
     return process(
         dataContext,
         manifest,
         ResourceDependencies.fromRuleDeps(ruleContext, neverlink),
         dataBindingContext,
-        linkResources);
+        linkResources,
+        namespacedRClass);
   }
 
   ValidatedAndroidResources process(
       AndroidDataContext dataContext,
       StampedAndroidManifest manifest,
       ResourceDependencies resourceDeps,
       DataBindingContext dataBindingContext,
-      boolean linkResources)
+      boolean linkResources,
+      boolean namespacedRClass)
       throws InterruptedException {
-    MergedAndroidResources merge = parse(dataContext, manifest, dataBindingContext)
-        .merge(dataContext, resourceDeps);
+    ParsedAndroidResources parse =
+        parse(dataContext, manifest, dataBindingContext, namespacedRClass);
+
+    MergedAndroidResources merge = namespacedRClass ?
+        parse.noMerge(dataContext, resourceDeps) :
+        parse.merge(dataContext, resourceDeps);
+
     return linkResources ? merge.validate(dataContext) : merge.validateNoLink(dataContext);
   }
 

src/main/java/com/google/devtools/build/lib/rules/android/AndroidResourcesProcessorBuilder.java

@@ -14,7 +14,6 @@
 package com.google.devtools.build.lib.rules.android;
 
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.rules.android.AndroidDataConverter.JoinerType;
@@ -215,6 +214,8 @@ public ProcessedAndroidData build(
             databindingProcessedResources,
             symbols,
             /* compiledSymbols = */ null,
+            /* classJarOut = */ null,
+            /* rTxtOut = */  null,
             dataContext.getLabel(),
             processedManifest,
             dataBindingContext);

src/main/java/com/google/devtools/build/lib/rules/android/AndroidStarlarkData.java

@@ -173,7 +173,8 @@ public ValidatedAndroidResources mergeRes(
                   Sequence.cast(deps, AndroidResourcesInfo.class, "deps"), neverlink),
               DataBinding.contextFrom(
                   enableDataBinding, ctx.getActionConstructionContext(), ctx.getAndroidConfig()),
-              ctx.getAndroidConfig().linkLibraryResources());
+              ctx.getAndroidConfig().linkLibraryResources(),
+              ctx.getAndroidConfig().namespacedRClass());
     } catch (RuleErrorException e) {
       throw handleRuleException(errorReporter, e);
     }
@@ -273,7 +274,8 @@ public Dict<Provider, NativeInfo> processAarImportData(
                     getProviders(depsTargets, AndroidResourcesInfo.PROVIDER),
                     /* neverlink = */ false),
                 DataBinding.getDisabledDataBindingContext(ctx),
-                ctx.getAndroidConfig().linkLibraryResources());
+                ctx.getAndroidConfig().linkLibraryResources(),
+                ctx.getAndroidConfig().namespacedRClass());
 
     MergedAndroidAssets mergedAssets =
         AndroidAssets.forAarImport(assets)

src/main/java/com/google/devtools/build/lib/rules/android/ParsedAndroidResources.java

@@ -29,6 +29,10 @@
 public class ParsedAndroidResources extends AndroidResources {
   @Nullable private final Artifact symbols;
   @Nullable private final Artifact compiledSymbols;
+  @Nullable
+  private final Artifact classJarOut;
+  @Nullable
+  private final Artifact rTxtOut;
   private final Label label;
   private final StampedAndroidManifest manifest;
   private final DataBindingContext dataBindingContext;
@@ -37,7 +41,8 @@ public static ParsedAndroidResources parseFrom(
       AndroidDataContext dataContext,
       AndroidResources resources,
       StampedAndroidManifest manifest,
-      DataBindingContext dataBindingContext)
+      DataBindingContext dataBindingContext,
+      boolean generateNamespacedRFiles)
       throws InterruptedException {
     AndroidResourceParsingActionBuilder builder = new AndroidResourceParsingActionBuilder();
 
@@ -47,6 +52,14 @@ public static ParsedAndroidResources parseFrom(
     AndroidResources databindingProcessedResources =
         dataBindingContext.processResources(dataContext, resources, manifest.getPackage());
 
+    if (generateNamespacedRFiles) {
+      builder
+          .setClassJarOut(
+              dataContext.createOutputArtifact(AndroidRuleClasses.ANDROID_RESOURCES_CLASS_JAR))
+          .setRTxtOut(dataContext.createOutputArtifact(AndroidRuleClasses.ANDROID_R_TXT))
+          .setManifest(manifest.getManifest());
+    }
+
     return builder
         .setCompiledSymbolsOutput(
             dataContext.createOutputArtifact(AndroidRuleClasses.ANDROID_COMPILED_SYMBOLS))
@@ -62,18 +75,22 @@ public static ParsedAndroidResources of(
       AndroidResources resources,
       @Nullable Artifact symbols,
       @Nullable Artifact compiledSymbols,
+      @Nullable Artifact classJarOut,
+      @Nullable Artifact rTxtOut,
       Label label,
       StampedAndroidManifest manifest,
       DataBindingContext dataBindingContext) {
     return new ParsedAndroidResources(
-        resources, symbols, compiledSymbols, label, manifest, dataBindingContext);
+        resources, symbols, compiledSymbols, classJarOut, rTxtOut, label, manifest, dataBindingContext);
   }
 
   ParsedAndroidResources(ParsedAndroidResources other, StampedAndroidManifest manifest) {
     this(
         other,
         other.symbols,
         other.compiledSymbols,
+        /* classJarOut= */ null,
+        /* rTxtOut= */ null,
         other.label,
         manifest,
         other.dataBindingContext);
@@ -83,12 +100,16 @@ protected ParsedAndroidResources(
       AndroidResources resources,
       Artifact symbols,
       @Nullable Artifact compiledSymbols,
+      @Nullable Artifact classJarOut,
+      @Nullable Artifact rTxtOut,
       Label label,
       StampedAndroidManifest manifest,
       DataBindingContext dataBindingContext) {
     super(resources);
     this.symbols = symbols;
     this.compiledSymbols = compiledSymbols;
+    this.classJarOut = classJarOut;
+    this.rTxtOut = rTxtOut;
     this.label = label;
     this.manifest = manifest;
     this.dataBindingContext = dataBindingContext;
@@ -104,6 +125,16 @@ public Artifact getCompiledSymbols() {
     return compiledSymbols;
   }
 
+  @Nullable
+  Artifact getAapt2RTxt() {
+    return rTxtOut;
+  }
+
+  @Nullable
+  public Artifact getClassJar() {
+    return classJarOut;
+  }
+
   public Iterable<Artifact> getArtifacts() {
     return getResources();
   }
@@ -134,6 +165,13 @@ MergedAndroidResources merge(AndroidDataContext dataContext, ResourceDependencie
     return MergedAndroidResources.mergeFrom(dataContext, this, resourceDeps);
   }
 
+  /** Skips merging this target's resources instead using artifacts produced at compilation. */
+  public MergedAndroidResources noMerge(AndroidDataContext dataContext,
+      ResourceDependencies resourceDeps) {
+    return MergedAndroidResources.of(this, null, this.classJarOut, this.rTxtOut,
+        null, resourceDeps, this.manifest.withProcessedManifest(this.manifest.getManifest()));
+  }
+
   @Override
   public Optional<? extends ParsedAndroidResources> maybeFilter(
       RuleErrorConsumer errorConsumer, ResourceFilter resourceFilter, boolean isDependency)
@@ -142,7 +180,7 @@ public Optional<? extends ParsedAndroidResources> maybeFilter(
         .map(
             resources ->
                 ParsedAndroidResources.of(
-                    resources, symbols, compiledSymbols, label, manifest, dataBindingContext));
+                    resources, symbols, compiledSymbols, null, null, label, manifest, dataBindingContext));
   }
 
   @Override

src/main/java/com/google/devtools/build/lib/rules/android/ValidatedAndroidResources.java

@@ -244,6 +244,8 @@ public ValidatedAndroidResources export() {
                 new AndroidResources(getResources(), getResourceRoots()),
                 getSymbols(),
                 getCompiledSymbols(),
+                null,
+                null,
                 getLabel(),
                 getStampedManifest(),
                 // Null out databinding to avoid accidentally propagating ActionCreationContext

src/test/java/com/google/devtools/build/lib/rules/android/AndroidResourcesTest.java

@@ -161,7 +161,8 @@ private void assertFilterValidated(
                 getManifest(),
                 DataBinding.contextFrom(ruleContext, dataContext.getAndroidConfig()),
                 /* neverlink = */ false,
-                /* linkResources */ true);
+                /* linkResources */ true,
+                AndroidDataContext.forNative(ruleContext).getAndroidConfig().namespacedRClass());
     Optional<? extends AndroidResources> maybeFiltered =
         assertFilter(unfiltered, filteredResources, /* isDependency = */ true);
 
@@ -423,7 +424,8 @@ private ParsedAndroidResources assertParse(
         raw.parse(
             AndroidDataContext.forNative(ruleContext),
             manifest,
-            dataBindingContext);
+            dataBindingContext,
+            AndroidDataContext.forNative(ruleContext).getAndroidConfig().namespacedRClass());
 
     // Inherited values should be equal
     assertThat(raw).isEqualTo(new AndroidResources(parsed));
@@ -459,7 +461,8 @@ private ParsedAndroidResources makeParsedResources(
         .parse(
             AndroidDataContext.forNative(ruleContext),
             getManifest(),
-            dataBindingContext);
+            dataBindingContext,
+            AndroidDataContext.forNative(ruleContext).getAndroidConfig().namespacedRClass());
   }
 
   private ProcessedAndroidManifest getManifest() {