Parse both old and new filenames from rename lines (R old -> new).
When diffing staged renames, use old filename as base to correctly
show content changes rather than treating the file as entirely new.
Also adds comprehensive tests for filename edge cases:
- Double extensions, hyphens, underscores, dotfiles
- Deep nested paths, complex renames
- Documents known limitation with filenames containing ' -> '
Section headers (Staged/Unstaged) now show all diffs in that section,
matching fugitive's behavior. Untracked files show as all-added diffs.
Deleted files show as all-removed diffs.
Also handles edge cases:
- Empty new/old content for deleted/new files
- Section header detection returns is_header flag
Compares current buffer against any git revision (default HEAD), opens result
with full diffs.nvim syntax highlighting. Follows fugitive convention:
:Gdiff/:Gvdiff open vertical split, :Ghdiff opens horizontal split.
Apply treesitter highlighting to diff metadata lines (diff --git, index,
---, +++) using the diff language parser. Header info is attached only
to the first hunk of each file to avoid duplicate highlighting.
Based on PR #52 by @phanen with fixes:
- header_lines now only contains diff metadata, not hunk content
- header info attached only to first hunk per file
- removed arbitrary hunk count restriction
