[9.0.1] Error on single_version_override patch with wrong patch_strip (#28566) (#28622)

Since diffs that don't apply to the MODULE.bazel file are silently
skipped (see
c413192),
this is needed to make users aware that their patch doesn't actually
apply to the file.

Fixes #28560

Closes #28566.

PiperOrigin-RevId: 868458465
Change-Id: I78d4027c5e8e01c2f5297e679c271bd4dac7b724

Commit
55312cc

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>

Author: bazel-io

src/main/java/com/google/devtools/build/lib/bazel/repository/decompressor/PatchUtil.java

@@ -447,6 +447,8 @@ private static void applyInternal(
       throw new PatchFailedException("Cannot find patch file: " + patchFile.getPathString());
     }
 
+    String singleFileStr =
+        singleFile != null ? singleFile.relativeTo(outputDirectory).getPathString() : null;
     boolean isGitDiff = false;
     boolean hasRenameFrom = false;
     boolean hasRenameTo = false;
@@ -594,6 +596,16 @@ private static void applyInternal(
                     oldFile, newFile, oldFileStr, newFileStr, patchStartLocation);
               }
             }
+            if (singleFileStr != null
+                && strip == 0
+                && ("a/" + singleFileStr).equals(oldFileStr)
+                && ("b/" + singleFileStr).equals(newFileStr)) {
+              throw new PatchFailedException(
+                  String.format(
+                      "error at line %d: the patch file contains a/b prefixes, did you forget to"
+                          + " set patch_strip = 1?",
+                      patchStartLocation));
+            }
 
             if (singleFile == null || (singleFile.equals(newFile) && singleFile.equals(oldFile))) {
               Patch<String> patch = UnifiedDiffUtils.parseUnifiedDiff(patchContent);

src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java

@@ -1875,6 +1875,47 @@ public void testSingleVersionOverridePatches() throws Exception {
             "ccc", InterimModule.DepSpec.fromModuleKey(new ModuleKey("ccc", Version.parse("2.0"))));
   }
 
+  @Test
+  public void testSingleVersionOverridePatches_defaultPatchStripForGitPatch() throws Exception {
+    FakeRegistry registry = registryFactory.newFakeRegistry("/foo");
+    ModuleFileFunction.REGISTRIES.set(differencer, ImmutableSet.of(registry.getUrl()));
+    ModuleKey bbb = createModuleKey("bbb", "1.0");
+    registry.addModule(bbb, "module(name='bbb',version='1.0')");
+
+    scratch.file("BUILD");
+    scratch.file(
+        "patch.diff",
+        """
+        diff --git a/MODULE.bazel b/MODULE.bazel
+        --- a/MODULE.bazel
+        +++ b/MODULE.bazel
+        @@ -1,1 +1,1 @@
+        -module(name='bbb',version='1.0')
+        +module(name='bbb',version='1.0',bazel_compatibility=[">=7.0.0"])
+        """);
+    scratch.overwriteFile(
+        rootDirectory.getRelative("MODULE.bazel").getPathString(),
+        """
+        single_version_override(
+          module_name="bbb",
+          patches = [
+            "//:patch.diff",
+          ],
+        )
+        """);
+
+    var moduleFileKey = ModuleFileValue.key(bbb);
+    EvaluationResult<ModuleFileValue> result =
+        evaluator.evaluate(ImmutableList.of(moduleFileKey), evaluationContext);
+    assertThat(result.hasError()).isTrue();
+    assertThat(result.getError().getException())
+        .hasMessageThat()
+        .isEqualTo(
+            "error applying single_version_override patch /workspace/patch.diff to module file:"
+                + " error at line 2: the patch file contains a/b prefixes, did you forget to set"
+                + " patch_strip = 1?");
+  }
+
   @Test
   public void testSingleVersionOverridePatches_failsOnRename() throws Exception {
     FakeRegistry registry = registryFactory.newFakeRegistry("/foo");