[wleeaf]

I'm an AI agent (Claude Opus 5.5, by Anthropic) acting through this account. I wrote this change and this description.

git turns the subsection name of a legacy header like [section.SubSection] into lower case, and then compares it case-sensitively (get_base_var() in config.c, and the git-config documentation: "the subsection name is converted to lower-case and is also compared case sensitively"). With

[Section.SubSection]
	Key = v

key	git config --get (2.43)	File::string() before	File::string() after
section.subsection.key	v	None	Some("v")
section.SubSection.key	not found	Some("v")	None
Section.SUBSECTION.KEY	not found	None	None

The crate documentation lists this as a known difference: "We keep its case and compare case-insensitively". But the section lookup tree used the subsection name as written, so the comparison was case-sensitive against the original case. section.subsection.key, which is how git reads this file, wasn't found.

Changes:

• HeaderData::subsection_lookup_name() returns the subsection name of legacy headers in lower case, and of other headers unchanged.
• The section lookup tree uses it everywhere it adds or removes a section: push_section_internal, insert_section_after, set_section_header and remove_section_by_id.
• The header itself keeps its original case. subsection_name() and serialization don't change.
• The "Known differences" note in lib.rs now describes this behaviour.

legacy_subsection_is_looked_up_in_lower_case in tests/config/file/access/read_only.rs checks the lower-case lookup, the mixed-case lookup and that the header keeps its original case (on [Remote.Origin]). It fails on main with left: None, right: Some("https://example.com").

cargo test -p gix-config --features sha1 passes, except for two tests that also fail on main with the git 2.43 on the machine I used: multi_line_value_starting_on_a_continuation_line_is_not_indented (git 2.43 turns the tab into a space) and source::git_config_no_system. cargo clippy -p gix-config --features sha1 --all-targets -- -D warnings and cargo fmt --check pass.

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	⚠️ Failed 2026-10-26T06:58:49.631102Z We couldn’t complete this review. Comment @codex review to try again.	e6b29cd	PR opened

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