Use ctime in file digest cache key

File digests are now additionally keyed by ctime for supported file
system implementations. Since Bazel has a non-zero default for
`--cache_computed_file_digests`, this may be required for correctness in
cases where different files have identical mtime and inode number.
For example, this can happen on Linux when files are extracted from a
tar file with fixed mtime and are then replaced with `mv`, which
preserves inodes.

src/main/java/com/google/devtools/build/lib/vfs/DigestUtils.java

@@ -46,6 +46,9 @@ private static class CacheKey {
     /** File system identifier of the file (typically the inode number). */
     private final long nodeId;
 
+    /** Last change time of the file. */
+    private final long changeTime;
+
     /** Last modification time of the file. */
     private final long modifiedTime;
 
@@ -62,6 +65,7 @@ private static class CacheKey {
     public CacheKey(Path path, FileStatus status) throws IOException {
       this.path = path.asFragment();
       this.nodeId = status.getNodeId();
+      this.changeTime = status.getLastChangeTime();
       this.modifiedTime = status.getLastModifiedTime();
       this.size = status.getSize();
     }
@@ -76,6 +80,7 @@ public boolean equals(Object object) {
         CacheKey key = (CacheKey) object;
         return path.equals(key.path)
             && nodeId == key.nodeId
+            && changeTime == key.changeTime
             && modifiedTime == key.modifiedTime
             && size == key.size;
       }
@@ -86,6 +91,7 @@ public int hashCode() {
       int result = 17;
       result = 31 * result + path.hashCode();
       result = 31 * result + Longs.hashCode(nodeId);
+      result = 31 * result + Longs.hashCode(changeTime);
       result = 31 * result + Longs.hashCode(modifiedTime);
       result = 31 * result + Longs.hashCode(size);
       return result;

src/test/shell/integration/execution_phase_tests.sh

@@ -369,4 +369,60 @@ function test_track_directory_crossing_package() {
       >& "$TEST_log" || fail "Expected success"
   expect_log "WARNING: Directory artifact foo/dir crosses package boundary into"
 }
+
+# Regression test for https://github.com/bazelbuild/bazel/issues/14723
+function test_fixed_mtime_move_detected_as_change() {
+  mkdir -p pkg
+  cat > pkg/BUILD <<'EOF'
+load("rules.bzl", "my_expand")
+
+genrule(
+    name = "my_templates",
+    srcs = ["template_archive.tar"],
+    outs = ["template1"],
+    cmd = "tar -C $(RULEDIR) -xf $<",
+)
+
+my_expand(
+    name = "expand1",
+    input = "template1",
+    output = "expanded1",
+    to_sub = {"test":"foo"}
+)
+EOF
+  cat > pkg/rules.bzl <<'EOF'
+def _my_expand_impl(ctx):
+    ctx.actions.expand_template(
+        template = ctx.file.input,
+        output = ctx.outputs.output,
+        substitutions = ctx.attr.to_sub
+    )
+
+my_expand = rule(
+    implementation = _my_expand_impl,
+    attrs = {
+        "input": attr.label(allow_single_file=True),
+        "output": attr.output(),
+        "to_sub" : attr.string_dict(),
+    }
+)
+EOF
+
+  echo "test : alpha" > template1
+  touch -t 197001010000 template1
+  tar -cf pkg/template_archive_alpha.tar template1
+
+  echo "test : delta" > template1
+  touch -t 197001010000 template1
+  tar -cf pkg/template_archive_delta.tar template1
+
+  mv pkg/template_archive_alpha.tar pkg/template_archive.tar
+  bazel build //pkg:expand1 || fail "Expected success"
+  assert_equals "foo : alpha" "$(cat bazel-bin/pkg/expanded1)"
+
+  mv pkg/template_archive_delta.tar pkg/template_archive.tar
+  bazel build //pkg:expand1 || fail "Expected success"
+  assert_equals "foo : delta" "$(cat bazel-bin/pkg/expanded1)"
+}
+
 run_suite "Integration tests of ${PRODUCT_NAME} using the execution phase."