Vim as one translation unit

This repository holds a process, not a product. It turns a pristine vim tree into a single C file — vim.c, about 182,000 lines — that one gcc invocation compiles into a working, standalone vim in roughly eight seconds.

Between passes there is no editor here. vim.c, the Makefile and LICENSE are products: they appear when you run a pass and are regenerated from upstream the next time. A fresh checkout containing only .gitignore, README.md, CLAUDE.md, GOAL.md and tools/ is the intended state, not a missing file.

What it is not

• Not a fork, and nothing is rebranded. The program is vim, the binary is vim, and $VIM, $VIMRUNTIME, ~/.vimrc and every string are upstream's. Whatever you call the checkout directory is not a name this tree uses.
• Not a feature-stripped vim. No feature was removed to get here: the reduction is in files and preprocessor, not in what the editor can do. The build is upstream's tiny configuration plus +extra_search.
• But it does not behave like a stock vim. It ships no vimrc, so what one would have said is compiled in instead: eighteen option defaults — among them tabstop=4, shiftwidth=4, softtabstop=4, expandtab, autoindent, nocompatible, hlsearch and ruler — plus four mappings, with bracketed paste never enabled. -u NONE does not undo any of it; these are the defaults. CLAUDE.md lists them all and says which half of each {vi, vim} pair was edited.
• Not one command. GOAL.md is a prompt for an agent, executed phase by phase with verification at every boundary. There is no run.sh.

The result has no preprocessor left in it: every directive in vim.c is one of 41 #includes of a system header. main() is the last thing in the file and the only symbol with external linkage.

Running a pass

Read GOAL.md first — all of it. The ordering is the point; four of its ten phases exist only to make the later ones safe.

git clone --branch regexp-delimiter-atoms --depth 1 \
    https://github.com/arbace/vim upstream
rm -rf upstream/.git                  # immediately: that remote is read-only input
#   ... GOAL.md Phases 0-9 run inside upstream/ ...
#   ... vim.c, the Makefile and LICENSE move to the repository root ...
rm -rf upstream                       # nothing else of it is kept

upstream/ is a staging directory, gitignored, and does not exist between passes. Everything this tree has is produced by those phases — there is no list of extras to re-apply afterwards, which is what makes the end-of-pass comparison mean anything.

Then build and check:

make                                  # one gcc invocation, ~8 s
tools/verify.sh .reference/baselines  # behaviour, Ex sweep, pty, terminals, warnings
tools/refcheck.sh                     # this pass against the previous pass's output

verify.sh compares the editor's behaviour against recordings made by an earlier pass; refcheck.sh compares the source and binary against that pass's output, which for an unchanged upstream should differ by nothing at all. Neither substitutes for the other. Both are optional on a first run, which has nothing to compare against and is self-certifying — say so rather than implying more.

Where to read what

Those two documents are the authority. This file is a front door and deliberately carries no figures that would go stale; CLAUDE.md's numbers are measurements, re-taken every pass.

Licence

Vim's own, unmodified, in LICENSE — clause II.1 requires it to ship with a modified Vim, and it is copied from the clone by each pass rather than maintained here.