llm-commit-helper

A smarter replacement for git diff --staged, designed to feed LLMs a clean, size-bounded summary of staged changes rather than raw diff noise.

The core problem with git diff --staged for LLM commit message generation:

• Large files (netlists, SVD files) flood the context window
• Reformatted Python files produce massive diffs with zero logic change
• Verilog AUTO-expanded sections (AUTOWIRE, AUTOINST, …) produce long, order-dependent diffs that obscure real changes
• Submodule updates show only a hash pair — no indication of what actually changed

llm-commit-helper handles all of these.

Requirements

• Python 3.11+
• git in PATH
• Optional: black (for Python formatting isolation)
• Optional: emacs with verilog-mode (for Verilog AUTO stripping)

No extra Python packages are required. Run directly from the source tree.

Installation

pip install -e /path/to/llm-commit-helper

Or from inside the project directory:

pip install -e .
# or
make install

Quick start

# From inside a git repository, with staged changes:
llm-commit-helper

Pipe the output to an LLM to generate a commit message:

llm-commit-helper | llm "Write a commit message"

Options

Output format

=== Staged Changes Summary ===
Files: 8 total (4 modified, 2 added, 1 excluded, 1 submodule)
Config: /home/user/project/config.jsonc

--- File: src/foo.py [modified] ---
@@ -10,6 +10,8 @@
 ...

--- File: src/bar.py [modified] [formatting-only] ---
[no logic changes - formatting only]

--- File: chip.netlist.v [excluded] ---
[changed - excluded by rule]

--- File: data/blob.bin [binary] ---
[binary file changed]

--- File: include/new_header.h [added] ---
[new file - contents not shown]

--- Submodule: support/imported/socbuilder ---
Updated: b2ae0f8 -> 153b625
  153b625 Update create_svd.py
  bfee9c1 feat(latex): Add LaTeX table generation

=== End of Staged Changes (3842 chars) ===

Diagnostic messages (config warnings, fallback notices) go to stderr. The staged-changes summary goes to stdout, so it can be piped cleanly.

File handling

Added files

New files are reported as [added] with no content. Adding file content to a commit message prompt is rarely useful and wastes context budget.

Deleted files

Reported as [deleted] with no diff shown.

Binary files

Detected via git diff --numstat (shows - - for binary). Reported as [binary file changed].

Excluded files

Files matching an exclude pattern in the config are reported as [changed - excluded by rule]. Useful for generated files, netlists, or anything too noisy to be useful in a commit message.

Files exceeding max_file_size

Reported as [changed - file too large]. Default threshold: 200 MB.

Submodules

For each updated submodule, the output includes a git log --oneline of the commits between the old and new hash. If the submodule is not initialized on disk, a warning is printed to stderr and the section is skipped.

Smart formatters

Python (.py)

Runs black --quiet on temporary copies of both the old and new versions of the file, then diffs the formatted results. If the formatted versions are identical, the file is marked [formatting-only] and no diff is shown. This suppresses the large diffs produced by black reformatting passes.

Falls back to generic formatting if black is not installed.

Verilog (.v, .sv)

Detects files using AUTO macros (AUTOARG, AUTOINPUT, AUTOOUTPUT, AUTOINST, AUTOWIRE, AUTOREG, …). When found, runs emacs --batch -f verilog-batch-delete-auto -f save-buffer on temporary copies of both versions to delete the AUTO-generated sections before diffing.

This is the correct approach: diffing the hand-written source (before AUTO expansion) rather than the expanded output, which is order-dependent and produces spurious diffs even when nothing real changed.

Falls back to generic formatting if emacs is not installed or if no AUTO macros are detected.

Generic (all other files)

Per-hunk whitespace normalization: strips leading/trailing whitespace and collapses internal runs of spaces/tabs, then checks if normalized removed and added lines are equal. Hunks that are whitespace-only are annotated [formatting-only] inline in the diff.

Configuration

llm-commit-helper searches for config.jsonc starting from the current working directory, walking up to the git root, then falling back to a global location. The first file found wins.

Search order:

1. <cwd>/config.jsonc
2. <cwd>/.llm-commit-helper/config.jsonc
3. Same two patterns repeated for each parent directory up to the git root
4. ~/.config/llm-commit-helper/config.jsonc

To skip the search and use a specific file:

python -m llm_commit_helper --config /path/to/my-config.jsonc

Config file format

The file is JSONC — standard JSON with // line comments and trailing commas allowed.

{
  "version": 1,
  "rules": {
    // Glob patterns for files to suppress (report as 'changed' only)
    "exclude": [
      "sim/firmware_ctests/**",
      "atpg/from_genus_1d-comp-sdf/chip.test_netlist.v",
      "*.netlist.v"
    ],

    // Files larger than this are suppressed (supports B, KB, MB, GB)
    "max_file_size": "200MB",

    // Total output budget; truncates with a summary when exceeded
    "max_total_size": 20000,
  }
}

Defaults (no config file)

Size values

max_file_size and max_total_size accept:

• Plain integers: 20000
• Suffixed strings: 200MB, 20KB, 1GB, 4096B
• max_total_size on the CLI (--max-total-size) accepts the same formats

Output truncation

When the accumulated output exceeds max_total_size, remaining files are listed by name only, followed by an [OUTPUT TRUNCATED] notice. The footer always shows the actual character count of the output produced.

Running tests

cd support/local/llm-commit-helper
python -m pytest tests/ -v
# or
make test

Tests use pytest with unittest.mock for all subprocess calls — no git repository or external tools required.

Project layout

llm_commit_helper/
├── __main__.py          # python -m llm_commit_helper entry point
├── cli.py               # argument parsing and main pipeline
├── config.py            # JSONC loading and hierarchical config search
├── git_staged.py        # staged file listing and classification
├── submodule.py         # submodule log retrieval and formatting
├── diff_engine.py       # difflib wrapper with formatting-only annotation
├── output.py            # size-budgeted output assembly
├── utils.py             # subprocess, size parsing, glob matching
└── formatters/
    ├── __init__.py      # extension-based dispatcher
    ├── generic_fmt.py   # whitespace normalization
    ├── python_fmt.py    # black-based logic/formatting separation
    └── verilog_fmt.py   # emacs AUTO deletion
tests/
├── test_config.py
├── test_formatters.py
├── test_git_staged.py
├── test_output.py
└── test_submodule.py