fix(isUnix): exempt final line before no-newline marker from CR check

release-notes.md

@@ -4,6 +4,7 @@
 
 - [#697](https://github.com/kpdecker/jsdiff/pull/697) *`diffJson` now correctly handles JSON objects containing a key named `__proto__`*. (Previously, the returned diff would be as if the `__proto__` key did not exist on either of the objects being diffed.)
 - [#700](https://github.com/kpdecker/jsdiff/pull/700) *`diffJson` now correctly handles JSON objects containing a non-callable property named `toJSON`* - i.e. it gives such a property no special behaviour whatsoever, just as `JSON.stringify` doesn't. Previously, such properties caused an error to be thrown. (*Callable* `toJSON` properties continue to get the same special behaviour that `JSON.stringify` gives them.)
+- [#701](https://github.com/kpdecker/jsdiff/pull/701) *`applyPatch` with `autoConvertLineEndings` on will no longer consider a stray `\r` character occurring at the end of a file without a terminating `\n` character to be a Windows line ending*, and so will no longer strip it when converting from Windows to Unix line endings or fail to apply a Unix-style patch to a Windows file when the patch introduces such a stray `\r`.
 
 ## 9.0.0
 

src/patch/line-endings.ts

@@ -55,7 +55,7 @@ export function isUnix(patch: StructuredPatch | StructuredPatch[]): boolean {
   return !patch.some(
     index => index.hunks.some(
       hunk => hunk.lines.some(
-        line => !line.startsWith('\\') && line.endsWith('\r')
+        (line, i) => !line.startsWith('\\') && line.endsWith('\r') && !hunk.lines[i + 1]?.startsWith('\\')
       )
     )
   );

test/patch/apply.js

@@ -1422,6 +1422,19 @@ describe('patch/apply', function() {
         .to.equal('');
     });
 
+    it('should correctly apply a Unix patch whose final added line ends with a literal \\r (no newline at EOF) to a Windows file', () => {
+      // The patch is Unix-style (no \\r\\n line endings), but the added line's content ends with a
+      // literal '\\r' because the new file has no trailing newline. autoConvertLineEndings must
+      // recognise the patch as Unix (not Windows), convert it to match the CRLF source, and apply
+      // it correctly — without dropping the literal '\\r'. Previously, isUnix() returned false for
+      // such a patch, so no conversion was attempted and applyPatch returned false.
+      const oldFileUnix = 'line1\nline2\n';
+      const newFileUnix = 'line1\nline3\r'; // final line has literal CR and no trailing newline
+      const patch = structuredPatch('test', 'test', oldFileUnix, newFileUnix, undefined, undefined, {context: 0});
+      const oldFileWin = 'line1\r\nline2\r\n';
+      expect(applyPatch(oldFileWin, patch)).to.equal('line1\r\nline3\r');
+    });
+
     it('should automatically convert a patch with Unix file endings to Windows when patching a Windows file', () => {
       const oldFile = 'foo\r\nbar\r\nbaz\r\nqux\r\n';
       const diffFile =

test/patch/line-endings.js

@@ -148,4 +148,19 @@ describe('isUnix', () => {
     );
     expect(isUnix(patch)).to.equal(true);
   });
+
+  it('should still return true if only the last line in a file has a CR and there is a no newline at EOF indicator', () => {
+    const patch = parsePatch(
+      'Index: test\n'
+      + '===================================================================\n'
+      + '--- test\theader1\n'
+      + '+++ test\theader2\n'
+      + '@@ -1,2 +1,3 @@\n'
+      + ' line2\n'
+      + ' line3\n'
+      + '+line4\r\n'
+      + '\\ No newline at end of file\n'
+    );
+    expect(isUnix(patch)).to.equal(true);
+  });
 });