fix: handle file mode changes (old mode/new mode) in diff parsing (#41)

* fix: handle file mode changes (old mode/new mode) in diff parsing

Files with `old mode`/`new mode` extended headers were not parsed
correctly, causing two bugs:

1. `new mode` lines were not recognized as extended headers. The
   ExtendedHeader constants included `Old: 'old'` which matches
   `old mode ...`, but only had `NewFile: 'new file'` for new-prefixed
   headers. Since `'new mode ...'` does not start with `'new file'`,
   `parseExtendedHeader` returned null, breaking the extended header
   loop prematurely.

2. When `parseFileChange` returned undefined (due to unrecognized
   headers and no matching return conditions), `parseFileChanges`
   used `break` instead of `continue`, causing ALL subsequent files
   in the diff to be silently dropped.

Fixes:
- Add `NewMode: 'new mode'` to ExtendedHeader constants
- Handle mode-only changes (no --- /+++ markers, no chunks) by
  falling back to the comparison line path
- Change `parseFileChanges` to skip unparseable entries instead of
  aborting the entire parse

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add changed mode data

* remove console.log

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: YeonJuan <yeonjuan93@naver.com>

Author: 3 people

.gitignore

@@ -11,3 +11,4 @@ demo/parse-git-diff.js
 !.yarn/sdks
 !.yarn/versions
 playground-out
+.DS_Store

.yarn/install-state.gz

@@ -0,0 +1,3 @@
+diff --git a/script.sh b/script.sh
+old mode 100644
+new mode 100755

src/__fixtures__/mode-change

@@ -0,0 +1,11 @@
+diff --git a/script.sh b/script.sh
+old mode 100644
+new mode 100755
+diff --git a/readme.md b/readme.md
+index abc1234..def5678 100644
+--- a/readme.md
++++ b/readme.md
+@@ -1,3 +1,3 @@
+ # Title
+-old content
++new content

src/__fixtures__/mode-change-followed-by-file

@@ -0,0 +1,10 @@
+diff --git a/script.sh b/script.sh
+old mode 100644
+new mode 100755
+index abc1234..def5678
+--- a/script.sh
++++ b/script.sh
+@@ -1,3 +1,3 @@
+ #!/bin/bash
+-echo "hello"
++echo "world"

src/__fixtures__/mode-change-with-content

@@ -0,0 +1,6 @@
+diff --git a/run.sh b/script.sh
+old mode 100755
+new mode 100644
+similarity index 100%
+rename from run.sh
+rename to script.sh

src/__fixtures__/mode-change-with-rename

@@ -1,4 +1,4 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
 exports[`issue 31-no-prefix parse \`31-no-prefix\` 1`] = `
 {
@@ -1177,6 +1177,8 @@ exports[`issue 31-no-prefix parse \`31-no-prefix\` 1`] = `
           "type": "Chunk",
         },
       ],
+      "newMode": undefined,
+      "oldMode": undefined,
       "path": "var/folders/kt/zd3bfncd0c3gjx25hbcq483c0000gn/T/epicshop/diff/advanced-react-apis/09.03.solution/dn2ncwjsbmo/index.tsx",
       "type": "ChangedFile",
     },

src/__tests__/__snapshots__/31-no-prefix.test.ts.snap

@@ -1,4 +1,4 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
 exports[`issue 31 parse \`31\` 1`] = `
 {
@@ -410,6 +410,8 @@ exports[`issue 31 parse \`31\` 1`] = `
           "type": "Chunk",
         },
       ],
+      "newMode": undefined,
+      "oldMode": undefined,
       "path": "var/folders/kt/zd3bfncd0c3gjx25hbcq483c0000gn/T/epicshop/diff/advanced-react-apis/04.01.solution/7h2jowvfi2q/index.tsx",
       "type": "ChangedFile",
     },

src/__tests__/__snapshots__/31.test.ts.snap

@@ -1,4 +1,4 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
 exports[`aa parse \`all\` 1`] = `
 {
@@ -31,6 +31,8 @@ exports[`aa parse \`all\` 1`] = `
           "type": "Chunk",
         },
       ],
+      "newMode": undefined,
+      "oldMode": undefined,
       "path": "rename.md",
       "type": "ChangedFile",
     },
@@ -112,11 +114,15 @@ exports[`aa parse \`all\` 1`] = `
           "type": "Chunk",
         },
       ],
+      "newMode": undefined,
+      "oldMode": undefined,
       "path": "rename.md",
       "type": "ChangedFile",
     },
     {
       "chunks": [],
+      "newMode": undefined,
+      "oldMode": undefined,
       "pathAfter": "rename.md",
       "pathBefore": "newfile.md",
       "type": "RenamedFile",

src/__tests__/__snapshots__/all.test.ts.snap

@@ -1,4 +1,4 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
+// Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
 exports[`chunk-context parse \`chunk-context\` 1`] = `
 {
@@ -31,6 +31,8 @@ exports[`chunk-context parse \`chunk-context\` 1`] = `
           "type": "Chunk",
         },
       ],
+      "newMode": undefined,
+      "oldMode": undefined,
       "path": "rename.js",
       "type": "ChangedFile",
     },