Add Watchman-backed DiffAwareness implementation

src/main/java/com/google/devtools/build/lib/skyframe/BUILD

@@ -1264,6 +1264,7 @@ java_library(
         ":broken_diff_awareness_exception",
         ":incompatible_view_exception",
         ":workspace_info",
+        "//src/main/java/com/google/devtools/build/lib/events",
         "//src/main/java/com/google/devtools/build/lib/vfs",
         "//src/main/java/com/google/devtools/common/options",
         "//third_party:guava",
@@ -1704,16 +1705,21 @@ java_library(
         "LocalDiffAwareness.java",
         "MacOSXFsEventsDiffAwareness.java",
         "WatchServiceDiffAwareness.java",
+        "WatchmanDiffAwareness.java",
     ],
     deps = [
         ":broken_diff_awareness_exception",
         ":diff_awareness",
         ":incompatible_view_exception",
+        "//src/main/java/com/google/devtools/build/lib/events",
         "//src/main/java/com/google/devtools/build/lib/jni",
+        "//src/main/java/com/google/devtools/build/lib/util",
         "//src/main/java/com/google/devtools/build/lib/util:os",
         "//src/main/java/com/google/devtools/build/lib/vfs",
         "//src/main/java/com/google/devtools/build/lib/vfs:pathfragment",
         "//src/main/java/com/google/devtools/common/options",
+        "//third_party:flogger",
+        "//third_party:gson",
         "//third_party:guava",
         "//third_party:jsr305",
     ],

src/main/java/com/google/devtools/build/lib/skyframe/DiffAwareness.java

@@ -14,6 +14,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.vfs.ModifiedFileSet;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.Root;
@@ -63,7 +64,8 @@ default WorkspaceInfoFromDiff getWorkspaceInfo() {
    *     {@link DiffAwareness} instance. The {@link DiffAwareness} is expected to close itself in
    *     this case.
    */
-  View getCurrentView(OptionsProvider options) throws BrokenDiffAwarenessException;
+  View getCurrentView(OptionsProvider options, EventHandler eventHandler)
+      throws BrokenDiffAwarenessException;
 
   /**
    * Returns the set of files of interest that have been modified between the given two views.

src/main/java/com/google/devtools/build/lib/skyframe/DiffAwarenessManager.java

@@ -115,7 +115,7 @@ public ProcessableModifiedFileSet getDiff(
     DiffAwareness diffAwareness = diffAwarenessState.diffAwareness;
     View newView;
     try (SilentCloseable c = Profiler.instance().profile("diffAwareness.getCurrentView")) {
-      newView = diffAwareness.getCurrentView(options);
+      newView = diffAwareness.getCurrentView(options, eventHandler);
     } catch (BrokenDiffAwarenessException e) {
       handleBrokenDiffAwareness(eventHandler, pathEntry, ignoredPaths, e);
       return BrokenProcessableModifiedFileSet.INSTANCE;

src/main/java/com/google/devtools/build/lib/skyframe/LocalDiffAwareness.java

@@ -20,6 +20,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.util.OS;
+import com.google.devtools.build.lib.util.OptionsUtils;
 import com.google.devtools.build.lib.vfs.ModifiedFileSet;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.lib.vfs.Root;
@@ -71,6 +72,19 @@ public static final class Options extends OptionsBase {
             "If true, experimental Windows support for --watchfs is enabled. Otherwise --watchfs"
                 + "is a non-op on Windows. Make sure to also enable --watchfs.")
     public boolean windowsWatchFS;
+
+    @Option(
+        name = "experimental_watchman_path",
+        defaultValue = "",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        converter = OptionsUtils.PathFragmentConverter.class,
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help =
+            "If set to a non-empty value, the specified Watchman binary will be used for file "
+                + "system watching instead of the builtin OS-specific file system watching "
+                + "mechanism. If only a basename is provided, the binary will be searched for in "
+                + "PATH.")
+    public PathFragment watchmanPath;
   }
 
   /** Factory for creating {@link LocalDiffAwareness} instances. */
@@ -106,14 +120,21 @@ public DiffAwareness maybeCreate(
           return null;
         }
       }
+
+      ImmutableSet<Path> ignoredNioPaths =
+          ignoredPaths.stream().map(p -> Path.of(p.toString())).collect(toImmutableSet());
+
+      PathFragment watchmanPath = optionsProvider.getOptions(Options.class).watchmanPath;
+      if (!watchmanPath.isEmpty()) {
+        return new WatchmanDiffAwareness(resolvedPathEntryFragment.toString(), ignoredNioPaths);
+      }
+
       // On OSX uses FsEvents due to https://bugs.openjdk.java.net/browse/JDK-7133447
       if (OS.getCurrent() == OS.DARWIN) {
         return new MacOSXFsEventsDiffAwareness(resolvedPathEntryFragment.toString());
       }
 
-      return new WatchServiceDiffAwareness(
-          resolvedPathEntryFragment.toString(),
-          ignoredPaths.stream().map(p -> Path.of(p.toString())).collect(toImmutableSet()));
+      return new WatchServiceDiffAwareness(resolvedPathEntryFragment.toString(), ignoredNioPaths);
     }
   }
 

src/main/java/com/google/devtools/build/lib/skyframe/MacOSXFsEventsDiffAwareness.java

@@ -16,6 +16,7 @@
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.jni.JniLoader;
 import com.google.devtools.common.options.OptionsProvider;
 import java.nio.file.Path;
@@ -129,7 +130,7 @@ public void close() {
   }
 
   @Override
-  public View getCurrentView(OptionsProvider options)
+  public View getCurrentView(OptionsProvider options, EventHandler eventHandler)
       throws BrokenDiffAwarenessException {
     if (!JNI_AVAILABLE) {
       return EVERYTHING_MODIFIED;

src/main/java/com/google/devtools/build/lib/skyframe/WatchServiceDiffAwareness.java

@@ -18,6 +18,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.HashBiMap;
 import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.util.OS;
 import com.google.devtools.common.options.OptionsProvider;
 import java.io.IOException;
@@ -70,7 +71,8 @@ private void init() {
   }
 
   @Override
-  public View getCurrentView(OptionsProvider options) throws BrokenDiffAwarenessException {
+  public View getCurrentView(OptionsProvider options, EventHandler eventHandler)
+      throws BrokenDiffAwarenessException {
     // We need to consider 4 cases for watchFs:
     // previous view    current view
     //  disabled         disabled  -> EVERYTHING_MODIFIED