Introduce a new SkyValue that merely contains the workspace name. The workspace name is needed for package loading, and so splitting out this computation into a separate skyframe node that can be change-pruned gives us better incrementality; previously we'd need to reload all packages on a WORKSPACE file change.

N.B.
(i) This CL doesn't solve all the other performance issues with //external in Bazel/Blaze since it's still inefficiently used for resolving labels like @foo//bar:baz.
(ii) This CL doesn't address the wasteful invalidation + change pruning of all the packages.

--
PiperOrigin-RevId: 146925369
MOS_MIGRATED_REVID=146925369

1 files changed, 102 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameValue.java
new file mode 100644
index 0000000000..9bfbfed3fc
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameValue.java
@@ -0,0 +1,102 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.skyframe;
+
+import com.google.devtools.build.lib.util.Preconditions;
+import com.google.devtools.build.skyframe.SkyKey;
+import com.google.devtools.build.skyframe.SkyValue;
+import java.util.Objects;
+import javax.annotation.Nullable;
+
+/**
+ * A value that solely represents the 'name' of a Bazel workspace, as defined in the WORKSPACE file.
+ *
+ * <p>This is a separate value with trivial change pruning so as to not necessitate a dependency
+ * from every {@link PackageValue} to the //external {@link PackageValue}, since such a
+ * hypothetical design would necessiate reloading all packages whenever there's a benign change to
+ * the WORKSPACE file.
+ */
+public class WorkspaceNameValue implements SkyValue {
+  private static final SkyKey KEY =
+      SkyKey.create(SkyFunctions.WORKSPACE_NAME, DummyArgument.INSTANCE);
+  private static final WorkspaceNameValue ERROR = new WorkspaceNameValue(null);
+
+  @Nullable
+  private final String workspaceName;
+
+  private WorkspaceNameValue(@Nullable String workspaceName) {
+    this.workspaceName = workspaceName;
+  }
+
+  /**
+   * Returns the name of the workspace, or {@code null} if there was an error in the WORKSPACE file.
+   */
+  @Nullable
+  public String maybeGetName() {
+    return workspaceName;
+  }
+
+  /** Returns the (singleton) {@link SkyKey} for {@link WorkspaceNameValue}s. */
+  public static SkyKey key() {
+    return KEY;
+  }
+
+  /** Returns a {@link WorkspaceNameValue} for a workspace whose WORKSPACE file is in error. */
+  public static WorkspaceNameValue withError() {
+    return WorkspaceNameValue.ERROR;
+  }
+
+  /** Returns a {@link WorkspaceNameValue} for a workspace with the given name. */
+  public static WorkspaceNameValue withName(String workspaceName) {
+    return new WorkspaceNameValue(Preconditions.checkNotNull(workspaceName));
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (!(obj instanceof WorkspaceNameValue)) {
+      return false;
+    }
+    WorkspaceNameValue other = (WorkspaceNameValue) obj;
+    return Objects.equals(workspaceName, other.workspaceName);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(workspaceName);
+  }
+
+  @Override
+  public String toString() {
+    return String.format("WorkspaceNameValue[name=%s]", workspaceName);
+  }
+
+  /** Singleton class used as the {@link SkyKey#argument} for {@link WorkspaceNameValue#key}. */
+  public static final class DummyArgument {
+    public static final int HASHCODE = DummyArgument.class.getCanonicalName().hashCode();
+    public static final DummyArgument INSTANCE = new DummyArgument();
+
+    private DummyArgument() {
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      return obj instanceof DummyArgument;
+    }
+
+    @Override
+    public int hashCode() {
+      return HASHCODE;
+    }
+  }
+}