Add support for GPG-signed commits (mystor#46)

GPG-sign commits if option -S/--gpg-sign is given, or if configurations
revise.gpgSign or commit.gpgSign are set to true.

In contrast to git-commit's options, the keyid used for signing cannot
(yet) be specified explicitly but by user.signingKey to prevent using
the committer signature as fallback.

A call of `git-revise COMMIT --gpg-sign` w/o any changes in the index
does not cause (re)creation of GPG commit signatures.

Signed-off-by: Nicolas Schier <nicolas@fjasle.eu>

git-revise.1

@@ -79,6 +79,12 @@ Reset target commit\(aqs author to the current user.
 .B \-\-ref <gitref>
 Working branch to update; defaults to \fBHEAD\fP\&.
 .UNINDENT
+.INDENT 0.0
+.TP
+\fB\-\-gpg-sign\fR, \fB\-S\fR, \fB\-\-no\-gpg\-sign
+GPG-sign commits.  To override the \fIcommit.gpgSign\fR git configuration, use
+\fI\-\-no\-gpg\-sign\fR.
+.UNINDENT
 .SS Main modes of operation
 .INDENT 0.0
 .TP
@@ -147,6 +153,14 @@ If set to true, imply \fI\%\-\-autosquash\fP whenever \fI\%\-\-interactive\fP
 is specified. Overridden by \fI\%\-\-no\-autosquash\fP\&. Defaults to false. If
 not set, the value of \fBrebase.autoSquash\fP is used instead.
 .UNINDENT
+.INDENT 0.0
+.TP
+.B revise.gpgSign
+If set to true, GPG-sign new commits; defaults to false.  This setting
+overrides the original git configuration \fBcommit.gpgSign\fR and may be
+overridden by the command line options \fI\-\-gpg\-sign\fR and
+\fI\-\-no\-gpg\-sign\fR.
+.UNINDENT
 .SH CONFLICT RESOLUTION
 .sp
 When a conflict is encountered, \fBgit revise\fP will attempt to resolve

gitrevise/odb.py

@@ -17,6 +17,8 @@
     Tuple,
     cast,
 )
+import subprocess
+from sys import stderr, exit
 from types import TracebackType
 from pathlib import Path
 from enum import Enum
@@ -134,6 +136,15 @@ class Repository:
     index: "Index"
     """current index state"""
 
+    sign_commits: False
+    """sign commits with gpg"""
+
+    key_id: ""
+    """key ID to be used for commit signing"""
+
+    gpg: "gpg"
+    """path to GnuPG binary"""
+
     _objects: Dict[int, Dict[Oid, "GitObj"]]
     _catfile: Popen
     _tempdir: Optional[TemporaryDirectory]
@@ -144,6 +155,8 @@ class Repository:
         "default_author",
         "default_committer",
         "index",
+        "sign_commits",
+        "key_id",
         "_objects",
         "_catfile",
         "_tempdir",
@@ -162,6 +175,22 @@ def __init__(self, cwd: Optional[Path] = None):
 
         self.index = Index(self)
 
+        self.sign_commits = self.bool_config(
+            "revise.gpgSign", default=self.bool_config("commit.gpgSign", default=False)
+        )
+
+        self.key_id = self.default_committer.name
+        if self.default_committer.email:
+            if self.key_id:
+                self.key_id += b" "
+                self.key_id += b"<" + self.default_committer.email + b">"
+            else:
+                self.key_id = self.default_committer.email
+
+        self.key_id = self.bool_config("user.signingKey", default=self.key_id)
+
+        self.gpg = self.config("gpg.program", default="gpg")
+
         self._catfile = Popen(
             ["git", "cat-file", "--batch"],
             bufsize=-1,
@@ -270,8 +299,25 @@ def new_commit(
             body += b"parent " + parent.oid.hex().encode() + b"\n"
         body += b"author " + author + b"\n"
         body += b"committer " + committer + b"\n"
-        body += b"\n"
-        body += message
+
+        body_tail = b"\n" + message
+
+        if self.sign_commits:
+            p = subprocess.run(
+                [self.gpg, "-bsau", self.key_id],
+                capture_output=True,
+                input=body + body_tail,
+            )
+            if not p.stdout:
+                print(p.stderr.decode(), file=stderr, end="")
+                print("gpg failed to sign commit", file=stderr)
+                exit(1)
+
+            body += b"gpgsig " + p.stdout.replace(b"\n", b"\n ")
+            body = body[:-1]
+
+        body += body_tail
+
         return Commit(self, body)
 
     def new_tree(self, entries: Mapping[bytes, "Entry"]) -> "Tree":

gitrevise/tui.py

@@ -88,6 +88,14 @@ def build_parser() -> ArgumentParser:
         action="store_true",
         help="interactively cut a commit into two smaller commits",
     )
+
+    mode_group = parser.add_mutually_exclusive_group()
+    mode_group.add_argument(
+        "--gpg-sign", "-S", action="store_true", default=None, help="GPG sign commits",
+    )
+    index_group.add_argument(
+        "--no-gpg-sign", action="store_false", help="do not GPG sign commits",
+    )
     return parser
 
 
@@ -192,6 +200,9 @@ def inner_main(args: Namespace, repo: Repository):
     if args.patch:
         repo.git("add", "-p")
 
+    if args.gpg_sign != None:
+        repo.sign_commits = args.gpg_sign
+
     # Create a commit with changes from the index
     staged = None
     if not args.no_index: