From e13958cd7545409cc444148707db3d104e82ef3f Mon Sep 17 00:00:00 2001
From: jhorvitz <jhorvitz@google.com>
Date: Mon, 25 Apr 2022 08:55:43 -0700
Subject: [PATCH] Add a flag `--rewind_lost_inputs` to toggle action rewinding.

The flag value is ignored unless other rewinding prerequisites are met.

PiperOrigin-RevId: 444281575
---
 .../lib/buildtool/BuildRequestOptions.java      | 10 ++++++++++
 .../lib/skyframe/SequencedSkyframeExecutor.java | 17 +++++++++++------
 .../skyframe/SequencedSkyframeExecutorTest.java | 13 ++++++++-----
 3 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java b/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
index 1f71794edbdcb3..9d1d087b4eefee 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/BuildRequestOptions.java
@@ -420,6 +420,16 @@ public boolean useTopLevelTargetsForSymlinks() {
       help = "Whether to store output metadata in the action cache")
   public boolean actionCacheStoreOutputMetadata;
 
+  @Option(
+      name = "rewind_lost_inputs",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.EXECUTION},
+      help =
+          "Whether to use action rewinding to recover from lost inputs. Ignored unless"
+              + " prerequisites for rewinding are met (no incrementality, no action cache).")
+  public boolean rewindLostInputs;
+
   @Option(
       name = "discard_actions_after_execution",
       defaultValue = "true",
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
index 27a46b17cd48d6..e1740db5cbd7ea 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
@@ -273,11 +273,10 @@ public WorkspaceInfoFromDiff sync(
       OptionsProvider options)
       throws InterruptedException, AbruptExitException {
     if (evaluatorNeedsReset) {
-      // Rewinding is only supported with no incremental state and no action cache.
       inconsistencyReceiver =
-          trackIncrementalState || useActionCache(options)
-              ? GraphInconsistencyReceiver.THROWING
-              : new RewindableGraphInconsistencyReceiver();
+          rewindingPermitted(options)
+              ? new RewindableGraphInconsistencyReceiver()
+              : GraphInconsistencyReceiver.THROWING;
       // Recreate MemoizingEvaluator so that graph is recreated with correct edge-clearing status,
       // or if the graph doesn't have edges, so that a fresh graph can be used.
       resetEvaluator();
@@ -300,9 +299,15 @@ public WorkspaceInfoFromDiff sync(
     return workspaceInfo;
   }
 
-  private static boolean useActionCache(OptionsProvider options) {
+  private boolean rewindingPermitted(OptionsProvider options) {
+    // Rewinding is only supported with no incremental state and no action cache.
+    if (trackIncrementalState) {
+      return false;
+    }
     BuildRequestOptions buildRequestOptions = options.getOptions(BuildRequestOptions.class);
-    return buildRequestOptions != null && buildRequestOptions.useActionCache;
+    return buildRequestOptions != null
+        && !buildRequestOptions.useActionCache
+        && buildRequestOptions.rewindLostInputs;
   }
 
   /**
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutorTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutorTest.java
index 611c13916ad79c..ff6567a0888e68 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutorTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutorTest.java
@@ -2478,20 +2478,23 @@ public NestedSet<Artifact> discoverInputs(ActionExecutionContext actionExecution
 
   @Test
   public void usesCorrectGraphInconsistencyReceiver(
-      @TestParameter boolean trackIncrementalState, @TestParameter boolean useActionCache)
+      @TestParameter boolean trackIncrementalState,
+      @TestParameter boolean useActionCache,
+      @TestParameter boolean rewindLostInputs)
       throws Exception {
     extraSkyFunctions.put(
         SkyFunctionName.FOR_TESTING,
         (key, env) -> {
-          if (trackIncrementalState || useActionCache) {
-            assertThat(env.restartPermitted()).isFalse();
-          } else {
+          if (!trackIncrementalState && !useActionCache && rewindLostInputs) {
             assertThat(env.restartPermitted()).isTrue();
+          } else {
+            assertThat(env.restartPermitted()).isFalse();
           }
           return new SkyValue() {};
         });
     initializeSkyframeExecutor();
-    options.parse("--use_action_cache=" + useActionCache);
+    options.parse(
+        "--use_action_cache=" + useActionCache, "--rewind_lost_inputs=" + rewindLostInputs);
 
     skyframeExecutor.setActive(false);
     skyframeExecutor.decideKeepIncrementalState(