fix(parser): support git diff.mnemonicPrefix in diff header

README.md

@@ -130,3 +130,5 @@ See the documentation for more information.
   decoration provider highlighting architecture, gitsigns blame popup
   highlighting, intra-line bg visibility fix
 - [@tris203](https://github.com/tris203) - support for transparent backgrounds
+- [@letientai299](https://github.com/letientai299) - `diff.mnemonicPrefix`
+  support

lua/diffs/parser.lua

@@ -248,7 +248,7 @@ function M.parse_buffer(bufnr)
       end
     end
 
-    local diff_git_file = logical:match('^diff %-%-git a/.+ b/(.+)$')
+    local diff_git_file = logical:match('^diff %-%-git %a/.+ %a/(.+)$')
       or logical:match('^diff %-%-combined (.+)$')
       or logical:match('^diff %-%-cc (.+)$')
     local neogit_file = logical:match('^modified%s+(.+)$')

spec/parser_spec.lua

@@ -262,6 +262,59 @@ describe('parser', function()
       delete_buffer(bufnr)
     end)
 
+    it('extracts filename with mnemonic prefix c/ i/', function()
+      local bufnr = create_buffer({
+        'diff --git c/init.lua i/init.lua',
+        'index 3e8afa0..018159c 100644',
+        '--- c/init.lua',
+        '+++ i/init.lua',
+        '@@ -1,1 +1,2 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('init.lua', hunks[1].filename)
+      assert.are.equal('lua', hunks[1].ft)
+      assert.are.equal('lua', hunks[1].lang)
+      delete_buffer(bufnr)
+    end)
+
+    it('extracts filename with mnemonic prefix w/ i/', function()
+      local bufnr = create_buffer({
+        'diff --git w/src/main.lua i/src/main.lua',
+        'index abc1234..def5678 100644',
+        '--- w/src/main.lua',
+        '+++ i/src/main.lua',
+        '@@ -1,1 +1,2 @@',
+        ' local M = {}',
+        '+local y = 2',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.are.equal('src/main.lua', hunks[1].filename)
+      delete_buffer(bufnr)
+    end)
+
+    it('rejects non-letter prefix in diff header', function()
+      local bufnr = create_buffer({
+        'diff --git 1/init.lua 2/init.lua',
+        'index 3e8afa0..018159c 100644',
+        '--- 1/init.lua',
+        '+++ 2/init.lua',
+        '@@ -1,1 +1,2 @@',
+        ' local M = {}',
+        '+local x = 1',
+      })
+      local hunks = parser.parse_buffer(bufnr)
+
+      assert.are.equal(1, #hunks)
+      assert.is_nil(hunks[1].filename)
+      delete_buffer(bufnr)
+    end)
+
     it('handles fugitive status format with diff headers', function()
       local bufnr = create_buffer({
         'Head: main',