git: Sign revup-created commits when commit.gpgSign is set

commit-tree (plumbing) ignores commit.gpgSign, so read it from git
config and pass -S explicitly. Read in the existing make_git async
gather alongside the other config lookups.

Co-Authored-By: Anurag Makineni <anurag.makineni@wayve.ai>

Author: jerry-skydio

revup/git.py

@@ -151,20 +151,29 @@ async def get_editor() -> str:
             ret = os.environ.get("GIT_EDITOR", os.environ.get("EDITOR", "nano"))
         return ret
 
+    async def get_gpg_sign() -> bool:
+        # commit-tree (plumbing) ignores commit.gpgSign, so read it and pass -S ourselves.
+        val = await git_ctx.git_stdout(
+            "config", "--type=bool", "--get", "commit.gpgSign", raiseonerror=False
+        )
+        return val.strip() == "true"
+
     (
         repo_root,
         git_dir,
         actual_version,
         email,
         editor,
         main_exists,
+        gpg_sign,
     ) = await asyncio.gather(
         git_ctx.git_stdout("rev-parse", "--show-toplevel"),
         git_ctx.git_stdout("rev-parse", "--path-format=absolute", "--git-dir"),
         git_ctx.git_stdout("--version"),
         get_email(),
         get_editor(),
         git_ctx.is_branch_or_commit(f"{remote_name}/{main_branch}"),
+        get_gpg_sign(),
     )
 
     if git_version:
@@ -184,6 +193,7 @@ async def get_editor() -> str:
     git_ctx.email = email.lower()
     git_ctx.author = git_ctx.email.split("@")[0]
     git_ctx.editor = editor
+    git_ctx.gpg_sign = gpg_sign
     if not main_exists:
         if main_branch in COMMON_MAIN_BRANCHES:
             git_ctx.main_branch = COMMON_MAIN_BRANCHES[1 - COMMON_MAIN_BRANCHES.index(main_branch)]
@@ -225,6 +235,9 @@ class Git:
     author: str
     editor: str
 
+    # Whether to GPG/SSH sign commits revup creates, from git config commit.gpgSign
+    gpg_sign: bool
+
     def __init__(
         self,
         sh: shell.Shell,
@@ -239,6 +252,7 @@ def __init__(
         self.remote_name = remote_name
         self.keep_temp = keep_temp
         self.main_branch = main_branch
+        self.gpg_sign = False
         self.base_branch_globs = base_branch_globs.strip().splitlines()
         self.temp_dir = tempfile.TemporaryDirectory(  # pylint: disable=consider-using-with
             prefix="revup_"
@@ -556,6 +570,8 @@ async def commit_tree(self, commit_info: CommitHeader) -> GitCommitHash:
             "-m",
             commit_info.commit_msg,
         ]
+        if self.gpg_sign:
+            commit_tree_args.append("-S")
         for p in commit_info.parents:
             commit_tree_args.extend(["-p", p])
         ret = await self.git_stdout(*commit_tree_args, env=git_env)