feat: rewrite config parser to be consistent with Git

Previously it was based on an ini-parser, which depends on the
Python version and also isn't actually dealing with the Git's
specific grammar and rules.

Now it's much more consistent, albeit probably also slower.

--- agent

Replace the line-oriented INI parsing logic in GitConfigParser with a
character-stream parser modeled on Git's config.c implementation.

The inherited configparser section matcher treats everything between the
first opening bracket and the last closing bracket as one section name.
Consequently, GitPython interpreted a header such as:

    [user] [other]

as one section named "user] [other", while Git interpreted it as two
successive section headers and assigned following values to "other".
Writing opaque section names through the INI serializer could therefore
change the configuration's meaning when Git subsequently read it.

Implement Git's configuration grammar directly, following the behavior of
git_parse_source(), get_base_var(), get_value(), and parse_value(). The new
parser handles:

- basic and quoted-subsection section headers
- multiple section headers in the same character stream
- comments introduced by '#' or ';'
- quoted and unquoted values
- supported backslash escapes
- backslash-newline continuations
- leading and trailing whitespace rules
- CRLF input and UTF-8 byte-order marks
- entries without values, represented semantically as boolean true
- duplicate options while preserving their order

Reject syntax that Git itself rejects, including colon delimiters,
underscore-containing option names, malformed section headers, unknown
value escapes, and unterminated quoted values.

Replace the raw value writer with a canonical Git-config serializer.
Values are always quoted, with backslashes, quotes, newlines, tabs, and
backspaces escaped. Quoted subsection names are parsed and re-escaped
canonically before being written. Comments and original whitespace remain
intentionally unpreserved when a dirty configuration is flushed.

Validate section names by parsing them as complete Git section headers.
This ensures each supplied name identifies exactly one section and
prevents unquoted closing brackets from injecting another section.
Validate option names against Git's ASCII letter, digit, and hyphen
grammar as well.

Update fixtures that previously depended on INI syntax rejected by Git,
and adjust expectations for decoded value escapes and valueless boolean
entries.

Add coverage for:

- the differing interpretation of adjacent section headers
- BOM, CRLF, comments, continuations, and valueless entries
- malformed syntax rejected by Git
- canonical value serialization and reparsing
- real `git config` interoperability
- closing brackets inside quoted subsection names
- quotes and backslashes inside subsection names
- invalid section and option names
- duplicate-value behavior with Git-compatible option names

Co-authored-by: Sebastian Thiel <sebastian.thiel@icloud.com>

Author: codex

git/config.py

@@ -4,6 +4,7 @@
 __all__ = ["Submodule", "UpdateProgress"]
 
 import gc
+from configparser import NoSectionError
 from io import BytesIO
 import logging
 import os
@@ -16,7 +17,7 @@
 import git
 from git.cmd import Git
 from git.compat import defenc
-from git.config import GitConfigParser, SectionConstraint, cp
+from git.config import GitConfigParser, SectionConstraint
 from git.exc import (
     BadName,
     InvalidGitRepositoryError,
@@ -172,7 +173,7 @@ def _set_cache_(self, attr: str) -> None:
             # Default submodule values.
             try:
                 self.path = reader.get("path")
-            except cp.NoSectionError as e:
+            except NoSectionError as e:
                 if self.repo.working_tree_dir is not None:
                     raise ValueError(
                         "This submodule instance does not exist anymore in '%s' file"
@@ -1503,7 +1504,7 @@ def exists(self) -> bool:
                 if hasattr(self, attr):
                     loc[attr] = getattr(self, attr)
                 # END if we have the attribute cache
-            except (cp.NoSectionError, ValueError):
+            except (NoSectionError, ValueError):
                 # On PY3, this can happen apparently... don't know why this doesn't
                 # happen on PY2.
                 pass

git/objects/submodule/base.py

@@ -110,7 +110,7 @@ def flush_to_index(self) -> None:
     # } END interface
 
     # { Overridden Methods
-    def write(self) -> None:  # type: ignore[override]
+    def write(self) -> None:
         rval: None = super().write()
         self.flush_to_index()
         return rval

git/objects/submodule/util.py

@@ -8,12 +8,13 @@
 __all__ = ["RemoteProgress", "PushInfo", "FetchInfo", "Remote"]
 
 import contextlib
+from configparser import NoOptionError, NoSectionError
 import logging
 import re
 
 from git.cmd import Git, handle_process_output
 from git.compat import defenc, force_text
-from git.config import GitConfigParser, SectionConstraint, cp
+from git.config import GitConfigParser, SectionConstraint
 from git.exc import GitCommandError
 from git.refs import Head, Reference, RemoteReference, SymbolicReference, TagReference
 from git.util import (
@@ -577,7 +578,7 @@ def __getattr__(self, attr: str) -> Any:
         # though a slot of the same name exists.
         try:
             return self._config_reader.get(attr)
-        except cp.NoOptionError:
+        except NoOptionError:
             return super().__getattr__(attr)
         # END handle exception
 
@@ -619,10 +620,10 @@ def exists(self) -> bool:
         try:
             self.config_reader.get("url")
             return True
-        except cp.NoOptionError:
+        except NoOptionError:
             # We have the section at least...
             return True
-        except cp.NoSectionError:
+        except NoSectionError:
             return False
 
     @classmethod

git/remote.py

@@ -22,8 +22,7 @@
 	url = git://gitorious.org/~martin.marcher/git-python/serverhorror.git
 	fetch = +refs/heads/*:refs/remotes/MartinMarcher/*
     # can handle comments - the section name is supposed to be stripped
-# causes stock git-config puke
-[  gui ]
+[gui]
 	geometry = 1316x820+219+243 207 192
 [branch "mainline_performance"]
 	remote = mainline
@@ -43,4 +42,3 @@
 # inclusions should be processed immediately
 [sec]
     var1 = value1_main
-

test/fixtures/git_config

@@ -4,4 +4,4 @@
 [section1]
     option1 = value1a
     option1 = value1b
-    other_option1 = other_value1
+    other-option1 = other_value1

test/fixtures/git_config_multiple

@@ -3,7 +3,5 @@
   hasbackslash = "foo\\bar"
   hasquote = "ab\"cd"
   hastrailingbackslash = "word\\"
-  hasunrecognized = "p\qrs"
-  hasunescapedquotes = "ab"cd"e"
   ordinary = "hello world"
   unquoted = good evening