Fix msg-filename kept open after edition (#491)

--msg-filename type is now a Path and not a managed click.File.
This makes it easier to control the opening and closing of the file.

Context manager will make sure that the file we use will be refreshed after
edition.

Co-authored-by: Maxime Roussin-Bélanger <maxime.roussinbelanger@gmail.com>

gitlint-core/gitlint/cli.py

@@ -5,6 +5,7 @@
 import stat
 import sys
 from dataclasses import dataclass
+from pathlib import Path
 from typing import Optional
 
 import click
@@ -185,7 +186,8 @@ def from_commit_msg(message):
     # 1. Any data specified via --msg-filename
     if msg_filename:
         LOG.debug("Using --msg-filename.")
-        return from_commit_msg(str(msg_filename.read()))
+        with msg_filename.open(encoding=gitlint.utils.FILE_ENCODING) as msg_file:
+            return from_commit_msg(str(msg_file.read()))
 
     # 2. Any data sent to stdin (unless stdin is being ignored)
     if not lint_config.ignore_stdin:
@@ -245,7 +247,7 @@ class ContextObj:
     config_builder: LintConfigBuilder
     commit_hash: str
     refspec: str
-    msg_filename: str
+    msg_filename: Optional[Path] = None
     gitcontext: Optional[GitContext] = None
 
 
@@ -270,7 +272,7 @@ class ContextObj:
 @click.option("--ignore", envvar="GITLINT_IGNORE", default="", help="Ignore rules (comma-separated by id or name).")
 @click.option("--contrib", envvar="GITLINT_CONTRIB", default="",
               help="Contrib rules to enable (comma-separated by id or name).")
-@click.option("--msg-filename", type=click.File(encoding=gitlint.utils.FILE_ENCODING),
+@click.option("--msg-filename", type=click.Path(exists=True, dir_okay=False, path_type=Path),
               help="Path to a file containing a commit-msg.")
 @click.option("--ignore-stdin", envvar="GITLINT_IGNORE_STDIN", is_flag=True,
               help="Ignore any stdin data. Useful for running in CI server.")
@@ -458,13 +460,10 @@ def run_hook(ctx):
                 exit_code = GITLINT_SUCCESS
             elif value == "e":
                 LOG.debug("run-hook: editing commit message")
-                msg_filename = ctx.obj.msg_filename
-                if msg_filename:
-                    msg_filename.seek(0)
+                if ctx.obj.msg_filename:
                     editor = os.environ.get("EDITOR", DEFAULT_COMMIT_MSG_EDITOR)
-                    msg_filename_path = os.path.realpath(msg_filename.name)
-                    LOG.debug("run-hook: %s %s", editor, msg_filename_path)
-                    shell(editor + " " + msg_filename_path)
+                    LOG.debug("run-hook: %s %s", editor, ctx.obj.msg_filename)
+                    shell(f"{editor} {ctx.obj.msg_filename}")
                 else:
                     click.echo("Editing only possible when --msg-filename is specified.")
                     ctx.exit(exit_code)