From f2a3c05ee74027d79b6465424d4c9ba79bd414bb Mon Sep 17 00:00:00 2001
From: Yoshiue <37270772+yoshi12u@users.noreply.github.com>
Date: Sun, 27 Jul 2025 09:13:08 +0900
Subject: [PATCH] feat: suggest commit messages from diff

---
 README.md            | 6 ++++++
 doc/copilot.txt      | 5 +++++
 lua/copilot/util.lua | 7 +++++++
 3 files changed, 18 insertions(+)

diff --git a/README.md b/README.md
index 0f9ed9e4..2096509c 100644
--- a/README.md
+++ b/README.md
@@ -299,6 +299,12 @@ require("copilot").setup {
 }
 ```
 
+### git commit messages
+
+When editing a commit message (`gitcommit` filetype), Copilot uses the staged
+diff (`git diff --staged`) to generate commit message suggestions. Enable
+`gitcommit` in the `filetypes` table to use this feature.
+
 ### logger
 
 Logs will be written to the `file` for anything of `file_log_level` or higher.
diff --git a/doc/copilot.txt b/doc/copilot.txt
index 2d62d298..4a0d3979 100644
--- a/doc/copilot.txt
+++ b/doc/copilot.txt
@@ -299,6 +299,11 @@ won’t be used anymore. e.g.
     }
 <
 
+GIT COMMIT MESSAGES~
+
+When editing a commit message (`gitcommit` filetype), Copilot fetches the
+staged diff (`git diff --staged`) to provide commit message suggestions. Enable
+`gitcommit` in the |copilot-filetypes| table to use this feature.
 
 LOGGER ~
 
diff --git a/lua/copilot/util.lua b/lua/copilot/util.lua
index 41b94e33..ab7b211c 100644
--- a/lua/copilot/util.lua
+++ b/lua/copilot/util.lua
@@ -74,6 +74,13 @@ function M.get_doc()
     position = params.position,
   }
 
+  if vim.bo.filetype == "gitcommit" then
+    local ok, diff = pcall(vim.fn.system, { "git", "diff", "--staged", "--no-color" })
+    if ok and diff and diff ~= "" then
+      doc.gitDiff = diff
+    end
+  end
+
   return doc
 end