From f65cf57d307279e7ba07f4c9f16be68b88a418ec Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Tue, 17 Mar 2026 17:09:06 -0400
Subject: [PATCH 1/2] fix(parser): support git diff.mnemonicPrefix in diff
 header

Problem: `git diff.mnemonicPrefix = true` produces diff headers like
`diff --git c/init.lua i/init.lua` using single-letter mnemonic
prefixes (`c/`, `i/`, `w/`) instead of the standard `a/`/`b/`.
The parser only matched `a/.+ b/(.+)`, so mnemonic-prefixed diffs
produced no highlighting.

Solution: Change the pattern to `%a/.+ %a/(.+)` (Lua `%a` matches
any letter), accepting any single-letter prefix while correctly
rejecting numeric prefixes like `1/`/`2/`. Adds tests for both
the accepted mnemonic cases and the rejected numeric case.
---
 README.md            |  1 +
 lua/diffs/parser.lua |  2 +-
 spec/parser_spec.lua | 53 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 8685ee0..0db28c7 100644
--- a/README.md
+++ b/README.md
@@ -130,3 +130,4 @@ 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
diff --git a/lua/diffs/parser.lua b/lua/diffs/parser.lua
index 6f84b83..09047a2 100644
--- a/lua/diffs/parser.lua
+++ b/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+(.+)$')
diff --git a/spec/parser_spec.lua b/spec/parser_spec.lua
index adbbd37..815032b 100644
--- a/spec/parser_spec.lua
+++ b/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',

From b6f16dfadf089b938799a2b5fddbc80f10439038 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Tue, 17 Mar 2026 17:13:44 -0400
Subject: [PATCH 2/2] ci: format

---
 README.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 0db28c7..cca39c7 100644
--- a/README.md
+++ b/README.md
@@ -130,4 +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
+- [@letientai299](https://github.com/letientai299) - `diff.mnemonicPrefix`
+  support