Add reduced repro tests for apply_patch parser mismatches

codex-rs/apply-patch/tests/suite/corpus_compare.rs

@@ -0,0 +1,118 @@
+use codex_apply_patch::Hunk;
+use codex_apply_patch::ParseError;
+use codex_apply_patch::StreamingPatchParser;
+use codex_apply_patch::parse_patch;
+
+#[derive(Debug, PartialEq)]
+enum CompareResult {
+    Match,
+    Mismatch {
+        legacy: Result<Vec<Hunk>, ParseError>,
+        streaming: Result<Vec<Hunk>, ParseError>,
+    },
+}
+
+fn parse_with_streaming_parser(patch: &str) -> Result<Vec<Hunk>, ParseError> {
+    let mut parser = StreamingPatchParser::default();
+    let mut last_hunks = None;
+    if let Some(hunks) = parser.push_delta(patch)? {
+        last_hunks = Some(hunks);
+    }
+    if !patch.ends_with('\n')
+        && let Some(hunks) = parser.push_delta("\n")?
+    {
+        last_hunks = Some(hunks);
+    }
+    Ok(last_hunks.unwrap_or_default())
+}
+
+fn compare_patch_outputs(patch: &str) -> CompareResult {
+    let legacy = parse_patch(patch).map(|args| args.hunks);
+    let streaming = parse_with_streaming_parser(patch);
+    if legacy == streaming {
+        CompareResult::Match
+    } else {
+        CompareResult::Mismatch { legacy, streaming }
+    }
+}
+
+#[test]
+fn reduced_repros_document_current_parser_mismatches() {
+    let cases = [
+        (
+            "empty update hunk is accepted by streaming parser",
+            "\
+*** Begin Patch
+*** Update File: foo.txt
+*** End Patch",
+        ),
+        (
+            "trailing empty update chunk before end patch is accepted",
+            "\
+*** Begin Patch
+*** Update File: foo.txt
+@@
+-old
++new
+@@
+*** End Patch",
+        ),
+        (
+            "trimmed nested add-file header inside update content is misparsed as syntax",
+            "\
+*** Begin Patch
+*** Update File: foo.txt
+@@
+-old
++new
+ *** Add File: nested.txt
+ +hello
+ *** End Patch
+*** End Patch",
+        ),
+        (
+            "trimmed nested context marker inside update content starts a new chunk",
+            "\
+*** Begin Patch
+*** Update File: foo.txt
+@@
+ line before
+ @@ nested
+-line after
++line after new
+*** End Patch",
+        ),
+        (
+            "trimmed nested end marker inside update content ends the patch early",
+            "\
+*** Begin Patch
+*** Update File: foo.txt
+@@
+-old
++new
+ *** End Patch
+ tail
+*** End Patch",
+        ),
+        (
+            "move-only update hunk is accepted and next hunk continues",
+            "\
+*** Begin Patch
+*** Update File: old.txt
+*** Move to: new.txt
+*** Update File: other.txt
+@@
+-before
++after
+*** End Patch",
+        ),
+    ];
+
+    for (name, patch) in cases {
+        let result = compare_patch_outputs(patch);
+        assert!(
+            matches!(result, CompareResult::Mismatch { .. }),
+            "{name}: expected mismatch, got {result:?}"
+        );
+    }
+}

codex-rs/apply-patch/tests/suite/mod.rs

@@ -1,4 +1,5 @@
 mod cli;
+mod corpus_compare;
 mod scenarios;
 #[cfg(not(target_os = "windows"))]
 mod tool;