Sort DirectoryNode children to ensure validity.

InputTree will create DirectoryNodes with non-sequential additions of
directory children. These must be maintained in order for representation
within remote Directory messages (and to properly compute action keys).

Co-Author=buchgr

Closes #8008.

PiperOrigin-RevId: 243235156

src/main/java/com/google/devtools/build/lib/remote/merkletree/InputTree.java

@@ -16,6 +16,7 @@
 import build.bazel.remote.execution.v2.Digest;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
+import com.google.common.collect.Sets;
 import com.google.devtools.build.lib.actions.ActionInput;
 import com.google.devtools.build.lib.actions.ActionInputHelper;
 import com.google.devtools.build.lib.actions.FileArtifactValue;
@@ -34,6 +35,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.SortedMap;
+import java.util.SortedSet;
 import java.util.TreeMap;
 
 /**
@@ -46,7 +48,7 @@ interface Visitor {
     void visitDirectory(PathFragment dirname, List<FileNode> files, List<DirectoryNode> dirs);
   }
 
-  abstract static class Node {
+  abstract static class Node implements Comparable<Node> {
     private final String pathSegment;
 
     Node(String pathSegment) {
@@ -57,6 +59,11 @@ String getPathSegment() {
       return pathSegment;
     }
 
+    @Override
+    public int compareTo(Node other) {
+      return pathSegment.compareTo(other.pathSegment);
+    }
+
     @Override
     public int hashCode() {
       return pathSegment.hashCode();
@@ -108,7 +115,7 @@ public boolean equals(Object o) {
   }
 
   static class DirectoryNode extends Node {
-    private final List<Node> children = new ArrayList<>();
+    private final SortedSet<Node> children = Sets.newTreeSet();
 
     DirectoryNode(String pathSegment) {
       super(pathSegment);

src/test/java/com/google/devtools/build/lib/remote/merkletree/InputTreeTest.java

@@ -169,6 +169,30 @@ public void directoryInputShouldBeExpanded() throws Exception {
     assertThat(fileNodesAtDepth(tree, 3)).containsExactly(expectedBuzzNode);
   }
 
+  @Test
+  public void testLexicographicalOrder() throws Exception {
+    // Regression test for https://github.com/bazelbuild/bazel/pull/8008
+    //
+    // The issue was that before #8008 we wrongly assumed that a sorted full list of inputs would
+    // also lead to sorted tree nodes. Thereby not taking into account that the path separator '/'
+    // influences the sorting of the full list but not that of the tree nodes as its stripped there.
+    // For example, the below full list is lexicographically sorted
+    //  srcs/system-root/bar.txt
+    //  srcs/system/foo.txt
+    //
+    // However, the tree node [system-root, system] is not (note the missing / suffix).
+
+    SortedMap<PathFragment, ActionInput> sortedInputs = new TreeMap<>();
+    Map<ActionInput, FileArtifactValue> metadata = new HashMap<>();
+
+    addFile("srcs/system/foo.txt", "foo", sortedInputs, metadata);
+    addFile("srcs/system-root/bar.txt", "bar", sortedInputs, metadata);
+
+    InputTree tree =
+        InputTree.build(sortedInputs, new StaticMetadataProvider(metadata), execRoot, digestUtil);
+    assertLexicographicalOrder(tree);
+  }
+
   private Artifact addFile(
       String path,
       String content,
@@ -193,28 +217,18 @@ private VirtualActionInput addVirtualFile(
   }
 
   private static void assertLexicographicalOrder(InputTree tree) {
-    int depth = 0;
-    while (true) {
-      // String::compareTo implements lexicographical order
-      List<String> files = filesAtDepth(depth, tree);
-      assertThat(files).isStrictlyOrdered();
-      List<String> directories = directoriesAtDepth(depth, tree);
-      assertThat(directories).isStrictlyOrdered();
-      if (directories.isEmpty()) {
-        break;
-      }
-      depth++;
-    }
+    // Assert the lexicographical order as defined by the remote execution protocol
+    tree.visit(
+        (PathFragment dirname, List<FileNode> files, List<DirectoryNode> dirs) -> {
+          assertThat(files).isStrictlyOrdered();
+          assertThat(dirs).isStrictlyOrdered();
+        });
   }
 
   private static List<String> directoriesAtDepth(int depth, InputTree tree) {
     return asPathSegments(directoryNodesAtDepth(tree, depth));
   }
 
-  private static List<String> filesAtDepth(int depth, InputTree tree) {
-    return asPathSegments(fileNodesAtDepth(tree, depth));
-  }
-
   private static List<String> asPathSegments(List<? extends Node> nodes) {
     return nodes.stream().map(Node::getPathSegment).collect(Collectors.toList());
   }