tiny-pattern-ts/scripts/branch.sh

#!/bin/sh

set -eu

# Branch front-door. Run as `npm run create:branch -- <prefix>/<desc>`.
#
# How we got here (short): the branching model says every change starts from a
# clean, current `main`, and the type-driven loop only produces trustworthy
# results if the baseline was green *before* the first edit. Both facts were
# prose. Prose rots silently — a rule nobody checks is a suggestion — so the
# precondition became this script: it asserts, then branches, and the branch
# only appears if the assertions passed. Cheap checks run first, `npm run test`
# runs last: the expensive gate is not paid on a tree that was never eligible.
#
# Rejected for the prefix name: `run:` / `perform:` (both mean only "do the
# thing named after them", so every script in the repo would fit under them and
# the taxonomy collapses); `git:` (names the tool, not the lifecycle moment, and
# advertises passthrough aliases); `start:` (describes this half, not the
# release); `cut:` (idiomatic for both, but it needs VCS slang to decode, and a
# signpost that has to be explained is not one); `flow:` (overloaded in a library
# about type-level matching); and the existing families — `check:*` is read-only
# and aggregated by `check`, so CI would run a command that mutates repo state;
# `fix:*`'s review surface is a file diff, not a branch; `maintain:*` is advisory
# and explicitly never a gate.
#
# `create:` was kept because both members really do create something: a branch,
# a release. It was added to both prefix lists in CONTRIBUTING.md in the same
# commit as its first members, because a prefix missing from those lists is
# invisible — which is the `use:` mistake this repo now carries in backlog.tasks.
# There is deliberately no bare `create` aggregator: "run all the workflows"
# describes nothing anyone wants, and `publish:*` already sets the precedent for
# a prefix without one.
#
# Also rejected: a full git-flow CLI wrapping the merge too (merging ends in
# "review the diff yourself", which is judgment, and only the start half carries
# a verification burden); and reusing `pubv`'s preflight (release-shaped,
# third-party, and it would make branch start pay a build + pack it has no use
# for).
#
# Every refusal is non-mutating except the baseline test, which runs on `main`
# after we switch there — so a red `main` restores the branch you started on
# rather than stranding you on it.

BASE="main"
PREFIXES="feature fix chore"
NAME="${1:-}"

if [ -z "${NAME}" ]; then
    echo "usage: npm run create:branch -- <prefix>/<desc>    (prefix: ${PREFIXES})" >&2
    exit 2
fi

git rev-parse --is-inside-work-tree >/dev/null 2>&1 || {
    echo "error: not inside a git work tree." >&2
    exit 1
}

MATCH=0
for p in ${PREFIXES}; do
    case "${NAME}" in
    "${p}/"*) MATCH=1 ;;
    esac
done
if [ "${MATCH}" -ne 1 ]; then
    echo "error: '${NAME}' must start with one of: ${PREFIXES}." >&2
    echo "       the prefix is inferred from the task, not defaulted here." >&2
    exit 1
fi
git check-ref-format --branch "${NAME}" >/dev/null 2>&1 || {
    echo "error: '${NAME}' is not a valid branch name." >&2
    exit 1
}
git show-ref --verify --quiet "refs/heads/${NAME}" && {
    echo "error: branch '${NAME}' already exists; switch to it instead." >&2
    exit 1
}

START_REF=$(git symbolic-ref --quiet --short HEAD || true)
if [ -z "${START_REF}" ]; then
    echo "error: detached HEAD; switch to a branch first." >&2
    exit 1
fi

STATE_ROOT=$(git rev-parse --absolute-git-dir)
for state in MERGE_HEAD rebase-merge rebase-apply CHERRY_PICK_HEAD BISECT_LOG; do
    [ -e "${STATE_ROOT}/${state}" ] && {
        echo "error: a '${state}' operation is in progress; finish or abort it first." >&2
        exit 1
    }
done
# `--porcelain` is deliberately stricter than `git diff --quiet`: it also reports
# untracked files, which would otherwise ride silently onto the new branch.
DIRTY=$(git status --porcelain)
if [ -n "${DIRTY}" ]; then
    echo "error: working tree is not clean:" >&2
    echo "${DIRTY}" | sed 's/^/         /' >&2
    exit 1
fi

git show-ref --verify --quiet "refs/heads/${BASE}" || {
    echo "error: no local '${BASE}' to branch from." >&2
    exit 1
}

# Derive the remote rather than hardcoding it: this repo has `origin` (ssh) and
# `origin_https`, and `main` tracks the latter — `git fetch origin main` would
# check currency against a ref that is never updated here.
UPSTREAM=$(git rev-parse --quiet --abbrev-ref --symbolic-full-name "${BASE}@{upstream}" 2>/dev/null || true)
if [ -n "${UPSTREAM}" ]; then
    git fetch --quiet "${UPSTREAM%/*}" "${UPSTREAM#*/}" || {
        echo "error: '${UPSTREAM}' check failed: could not reach '${UPSTREAM%/*}'." >&2
        echo "       refusing to branch on a possibly stale '${BASE}'." >&2
        exit 1
    }
    BEHIND=$(git rev-list --count "${BASE}..${UPSTREAM}")
    AHEAD=$(git rev-list --count "${UPSTREAM}..${BASE}")
    if [ "${BEHIND}" -ne 0 ] || [ "${AHEAD}" -ne 0 ]; then
        echo "error: '${BASE}' has diverged from '${UPSTREAM}' (ahead ${AHEAD}, behind ${BEHIND})." >&2
        [ "${AHEAD}" -ne 0 ] && echo "       not yet pushed commits on '${BASE}': push them, or rebase this work onto them." >&2
        [ "${BEHIND}" -ne 0 ] && echo "       update it: git switch ${BASE} && git pull --ff-only" >&2
        exit 1
    fi
else
    echo "warning: '${BASE}' has no upstream; freshness against the remote is unchecked." >&2
fi

restore() {
    git switch --quiet "${START_REF}" 2>/dev/null || true
}
trap 'restore' EXIT HUP INT TERM

if [ "${START_REF}" != "${BASE}" ]; then
    git switch --quiet "${BASE}"
fi

echo "Baseline: npm run test"
if ! npm run --silent test; then
    echo "error: baseline is red on '${BASE}'; fix that first so later failures stay attributable." >&2
    exit 1
fi

git switch --quiet --no-track -c "${NAME}"
trap - EXIT HUP INT TERM

# push.default=upstream is set here, so an inherited upstream would make a bare
# `git push` target main. Branching local-from-local does not set one anyway;
# --no-track says so out loud.
echo "Created ${NAME} from ${BASE} $(git rev-parse --short "${BASE}")."