Make repo marker file parsing robust to version changes

Bazel 7.1.0 and 7.2.0 contains a bug where + characters in labels in the repository marker files cannot be parsed. This was fixed in commit d62e0a0. To reduce the rusk of future bugs in the same area, this change skips parsing the file if the first line shows that the content will not be used anyway, which should be reasonably safe if introducing new formats.

Improves #23336 that fixed #23322.

Closes #23642.

PiperOrigin-RevId: 679330823
Change-Id: I8123bdde047735ced3eabed3df68112d44318b08

src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryDelegatorFunction.java

@@ -621,6 +621,10 @@ static String unescape(String str) {
   }
 
   private static class DigestWriter {
+    // Input value map to force repo invalidation.
+    private static final ImmutableMap<RepoRecordedInput, String> NOT_UP_TO_DATE =
+        ImmutableMap.of(RepoRecordedInput.NEVER_UP_TO_DATE, "");
+
     private final BlazeDirectories directories;
     private final Path markerPath;
     private final Rule rule;
@@ -681,43 +685,41 @@ byte[] areRepositoryAndMarkerFileConsistent(
         return null;
       }
 
-      Map<RepoRecordedInput, String> recordedInputValues = new TreeMap<>();
-      String content;
       try {
-        content = FileSystemUtils.readContent(markerPath, UTF_8);
-        String markerRuleKey = readMarkerFile(content, recordedInputValues);
-        boolean verified = false;
-        if (Preconditions.checkNotNull(ruleKey).equals(markerRuleKey)) {
-          verified = handler.verifyRecordedInputs(rule, directories, recordedInputValues, env);
-          if (env.valuesMissing()) {
-            return null;
-          }
+        String content = FileSystemUtils.readContent(markerPath, UTF_8);
+        Map<RepoRecordedInput, String> recordedInputValues =
+            readMarkerFile(content, Preconditions.checkNotNull(ruleKey));
+        if (!handler.verifyRecordedInputs(rule, directories, recordedInputValues, env)) {
+          return null;
         }
-
-        if (verified) {
-          return new Fingerprint().addString(content).digestAndReset();
-        } else {
+        if (env.valuesMissing()) {
           return null;
         }
+        return new Fingerprint().addString(content).digestAndReset();
       } catch (IOException e) {
         throw new RepositoryFunctionException(e, Transience.TRANSIENT);
       }
     }
 
     @Nullable
-    private static String readMarkerFile(
-        String content, Map<RepoRecordedInput, String> recordedInputValues) {
-      String markerRuleKey = null;
+    private static Map<RepoRecordedInput, String> readMarkerFile(
+        String content, String expectedRuleKey) {
       Iterable<String> lines = Splitter.on('\n').split(content);
 
-      boolean firstLine = true;
+      @Nullable Map<RepoRecordedInput, String> recordedInputValues = null;
+      boolean firstLineVerified = false;
       for (String line : lines) {
         if (line.isEmpty()) {
           continue;
         }
-        if (firstLine) {
-          markerRuleKey = line;
-          firstLine = false;
+        if (!firstLineVerified) {
+          if (!line.equals(expectedRuleKey)) {
+            // Break early, need to reload anyway. This also detects marker file version changes
+            // so that unknown formats are not parsed.
+            return NOT_UP_TO_DATE;
+          }
+          firstLineVerified = true;
+          recordedInputValues = new TreeMap<>();
         } else {
           int sChar = line.indexOf(' ');
           if (sChar > 0) {
@@ -728,12 +730,13 @@ private static String readMarkerFile(
             }
           }
           // On parse failure, just forget everything else and mark the whole input out of date.
-          recordedInputValues.clear();
-          recordedInputValues.put(RepoRecordedInput.NEVER_UP_TO_DATE, "");
-          break;
+          return NOT_UP_TO_DATE;
         }
       }
-      return markerRuleKey;
+      if (!firstLineVerified) {
+        return NOT_UP_TO_DATE;
+      }
+      return Preconditions.checkNotNull(recordedInputValues);
     }
 
     private String computeRuleKey(Rule rule, StarlarkSemantics starlarkSemantics) {

src/test/shell/bazel/starlark_repository_test.sh

@@ -2895,6 +2895,14 @@ EOF
   bazel shutdown
   bazel build @foo >& $TEST_log || fail "expected bazel to succeed"
   expect_log "I see: nothing"
+
+  # Test to clear the marker file.
+  echo > ${marker_file}
+
+  # Running Bazel again shouldn't crash, and should result in a refetch.
+  bazel shutdown
+  bazel build @foo >& $TEST_log || fail "expected bazel to succeed"
+  expect_log "I see: nothing"
 }
 
 function test_file_watching_in_undefined_repo() {