#!/usr/bin/env bash
# Does this change touch anything that can move the compiler? Prints `true`
# or `false` on stdout and ALWAYS exits 0, so a caller can put the answer
# straight into `$GITHUB_OUTPUT` without a failing status turning the step
# red. Usage:
#
#   scripts/ci-compiler-relevant.sh <base-revision> [head-revision]
#
# It exists because the two expensive CI jobs (`test`, 54 min, and
# `bootstrap`, 22 min) cannot be affected by a change that only touches
# prose -- and a docs-only change is exactly the traffic that fills the
# runner queue, where every queued minute is paid by an unrelated branch.
#
# A workflow-level `paths-ignore` would be shorter and is WRONG here, for
# two reasons that were checked rather than assumed:
#
#   * `docs-check` is a pre-commit hook (devenv.nix -> scripts/check-docs.sh,
#     which type-checks every code block under docs/). So a docs-only change
#     is NOT a change CI can ignore wholesale: it still needs the
#     `pre-commit-checks` job. A workflow-level filter would skip that too,
#     which is a missed signal rather than a saving. Only the two compiler
#     jobs are gated, and this script only decides whether they can see the
#     change.
#
#     That is the ONLY docs gate in this repository, which is why the point
#     is not academic: `gh workflow list --all` reports just three workflows
#     here -- CI, "Nightly release" (active, but its single job is gated on
#     `github.repository == 'monad-lang/monad'`, never this remote, so it runs
#     nothing) and "Deploy mdBook site to Pages" (disabled_manually, and it
#     builds and deploys a site rather than checking any code block). Round
#     1's changes to those two files are unobservable in this repository.
#   * `paths-ignore` on `pull_request` skips the whole workflow, and a
#     skipped workflow leaves its required status checks PENDING -- GitHub's
#     documented behaviour -- so on a repository with required checks the
#     filter blocks the merge instead of saving an hour. Whether this
#     repository has them could not be verified from here (the PAT is not
#     allowed to read branch protection), so the design has to be correct
#     either way: a job-level skip reports a verdict.
#
# A third reason is local to this corpus: `bench/` and `proofs/` are in
# `check-monad-tests.sh`'s `corpus_dirs`, so their `.mo` files ARE swept.
# Ignoring those trees wholesale would skip real signal; only their markdown
# is ignorable, which is what the `*.md` rule below does.
#
# THE DECISION FAILS OPEN. An empty diff, an all-zeros or unreachable base
# (`github.event.before` on a new branch), an unknown event, or any git
# error all answer `true`. That is the only acceptable direction: a
# misclassification may then cost an hour of runner time, never a missed
# failure. The rules below are the paths a change can touch without the
# compiler reading them -- markdown in any directory, the generated mdbook
# under docs/, and files no build in this repository opens.
set -euo pipefail

base="${1:-}"
head="${2:-HEAD}"

files=""
if [ -n "$base" ] && ! printf '%s' "$base" | grep -qE '^0+$' \
  && git rev-parse --verify --quiet "${base}^{commit}" > /dev/null 2>&1; then
  files="$(git diff --name-only "$base" "$head" 2> /dev/null)" || files=""
fi

if [ -z "$files" ]; then
  echo true
  exit 0
fi

while IFS= read -r path; do
  [ -n "$path" ] || continue
  case "$path" in
    # Markdown is prose wherever this repository keeps it: the root
    # README/AGENTS/CODE_OF_CONDUCT, docs/src's book sources, the
    # per-directory READMEs, and .claude-plugin's.
    *.md) ;;
    # The mdbook's config and its COMMITTED build output (docs/book/*.html).
    # Generated, and nothing compiles it -- mdbook.yml is disabled_manually.
    docs/*) ;;
    # Opened by no nix expression, script or hook in the tree: nix's
    # `meta.license` names a nixpkgs value, not this file, and the ignore
    # rules are consumed by git itself.
    LICENSE | .gitignore) ;;
    # Agent/plugin configuration. Not read by any CI step -- the pre-commit
    # hooks come from .pre-commit-config.yaml, generated by devenv.
    .claude-plugin/*) ;;
    *) echo true; exit 0 ;;
  esac
done <<< "$files"

echo false