Quilt.cpp: implementation of Quilt in C++

Quilt.cpp is a clone of Quilt in C++20. The original is a collection of Bash scripts driving Coreutils, plus a bit of Perl. It does not support native Windows. In contrast, Quilt.cpp is a standalone, native application intended to complement w64devkit. It embeds a diff and patch, and so does not depend on any external tool except $EDITOR.

This project is a clean-room AI rewrite. AI generated the tests based on the Quilt documentation, online tutorials, and observing the original's behavior in various scenarios. The tests then served as a conformance suite for its own from-scratch Quilt implementation. Every line outside this README.md is written by AI. The original, feature complete — less deliberately omitted features listed below — was written with Claude Code over the course of four days.

Build

$ cmake -B build
$ cmake --build build

Tip: Set CMAKE_BUILD_PARALLEL_LEVEL for faster builds. To build the Windows amalgamation source, quilt.cpp, for easy distribution:

$ cmake --build -t amalgam

Then later without any build system:

$ c++ -std=c++20 -o quilt.exe quilt.cpp -lshell32

Or with MSVC:

$ cl /std:c++20 /EHsc quilt.cpp shell32.lib

Tests

$ cmake --build -build -t test

Tip: Set CTEST_PARALLEL_LEVEL for faster builds. Run tests against any Quilt using QUILT_TEST_EXECUTABLE:

$ cmake -B build -DQUILT_TEST_EXECUTABLE=/bin/quilt
$ cmake --build -build -t test

The purpose is validate the tests against the original Quilt.

Differences from Quilt

quilt mail

The original Quilt mail command is designed for emailing patches to mailing lists. It supports --send (direct SMTP via sendmail) and --mbox (write to a file), and it always generates a cover letter as the first message (patch 0/N), opening $EDITOR for its contents.

Quilt.cpp targets a different workflow: generating an mbox that can be applied on another machine with git am. The output format closely matches git format-patch --stdout so that subjects, commit messages, and authorship round-trip through git am. --send is unsupported.

To avoid passing --from every invocation, set a default in ~/.quiltrc:

QUILT_MAIL_ARGS='--from "First Last <user@example.com>" --mbox patches.mbox'

Shell-like splitting for QUILT_*_ARGS

The original Quilt is a Bash script, and variables like QUILT_MAIL_ARGS are eval'd with full shell syntax. Quilt.cpp implements a purpose-built splitter that covers the useful subset: single quotes (literal, no escapes), double quotes (with \", \\, \$ escapes), $VAR and ${VAR} expansion, and backslash escapes in unquoted text. Adjacent quoted and unquoted segments merge into a single token, just as in a shell. This applies to all QUILT_*_ARGS and QUILT_*_OPTS variables.

Deliberately omitted features

Quilt.cpp omits setup because it's an old, RPM-specific workflow that won't benefit from this rewrite. It omits grep because it's merely a wrapper around an external grep, which exists mainly because it's easy to do from a shell script. The shell command is to help work around the Quilt's untracked-file limitations, but it's blunt, and like grep it's a natural outgrowth of the original's shell-script nature.

There is no built-in pager support. LESS and QUILT_PAGER do nothing.

The --color option is parsed, validated, and discarded. QUILT_COLORS is not examined. Quilt.cpp does not produce color output because it is not intended for children.