homebrew tap for mcpp: prebuilt release formula + automated bump

Formula/mcpp-m.rb ships the same prebuilt artifacts install.sh downloads,
verified against upstream's .sha256 sidecars.

Two things this repo exists to get right:

- The formula installs the self-contained tree under libexec and puts a
  launcher on PATH. mcpp derives MCPP_HOME from the canonicalized path of
  the running binary, so a plain symlink into bin would make the Cellar
  version directory its home -- registry, caches and every downloaded
  toolchain would be discarded by the next 'brew upgrade'.

- The name. homebrew-core owns 'mcpp' (Matsui's C preprocessor), so the
  formula is mcpp-m, with Aliases/{mcpp,mcpp-bin} pointing here. Same
  collision, same resolution as upstream's AUR packages.

Author: speak-agent

.github/workflows/bump-formula.yml

@@ -0,0 +1,68 @@
+name: bump-formula
+
+# Keep Formula/mcpp-m.rb pointed at the newest mcpp release.
+#
+# Three ways in, deliberately:
+#   repository_dispatch — upstream's release pipeline pings us the moment a
+#                         release finishes (needs a PAT on the upstream side).
+#   schedule            — daily catch-up, so the tap self-heals even with no
+#                         token configured upstream. This is the safety net,
+#                         not the primary path.
+#   workflow_dispatch   — manual pin / re-run.
+#
+# All three converge on scripts/update-formula.sh, which reads the sha256
+# sidecars upstream publishes and refuses to write a half-rewritten formula.
+
+on:
+  repository_dispatch:
+    types: [mcpp-release]
+  workflow_dispatch:
+    inputs:
+      version:
+        description: "mcpp version to pin (blank = upstream latest)"
+        required: false
+  schedule:
+    - cron: "23 4 * * *"
+
+permissions:
+  contents: write
+
+concurrency:
+  group: bump-formula
+  cancel-in-progress: false
+
+jobs:
+  bump:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Resolve target version
+        id: ver
+        run: |
+          # Empty on the schedule trigger — update-formula.sh then resolves
+          # upstream's latest release itself.
+          V="${{ github.event.client_payload.version }}"
+          [ -n "$V" ] || V="${{ github.event.inputs.version }}"
+          echo "version=${V}" >> "$GITHUB_OUTPUT"
+          echo ":: requested version: ${V:-<latest>}"
+
+      - name: Update the formula
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: ./scripts/update-formula.sh ${{ steps.ver.outputs.version }}
+
+      - name: Commit and push
+        run: |
+          set -eu
+          if git diff --quiet -- Formula; then
+            echo ":: formula already current — nothing to commit"
+            exit 0
+          fi
+          VER=$(sed -nE 's/^[[:space:]]*version "([^"]+)".*/\1/p' Formula/mcpp-m.rb | head -1)
+          git config user.name  "mcpp-ci"
+          git config user.email "x.d2learn.org@gmail.com"
+          git commit -qam "mcpp ${VER}"
+          git push
+          echo ":: pushed mcpp ${VER}"
+          echo "Bumped the formula to **${VER}**." >> "$GITHUB_STEP_SUMMARY"

.github/workflows/ci.yml

@@ -0,0 +1,31 @@
+name: ci
+
+# Cheap structural checks. A tap's real test is `brew install`, which needs a
+# macOS runner and downloads a toolchain — too heavy to run per push, so it
+# stays a manual `brew install --verbose --debug` before publishing changes.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Formula parses as Ruby
+        run: ruby -c Formula/*.rb
+
+      - name: Shell scripts lint clean
+        run: shellcheck scripts/*.sh
+
+      - name: Aliases resolve to a real formula
+        run: |
+          set -eu
+          for a in Aliases/*; do
+            target=$(readlink "$a") || { echo "error: $a is not a symlink"; exit 1; }
+            [ -f "Aliases/$target" ] || { echo "error: $a -> $target is dangling"; exit 1; }
+            echo ":: $a -> $target"
+          done

Aliases/mcpp

@@ -0,0 +1 @@
+../Formula/mcpp-m.rb

Aliases/mcpp-bin

@@ -0,0 +1 @@
+../Formula/mcpp-m.rb

Formula/mcpp-m.rb

@@ -0,0 +1,97 @@
+# mcpp — modern C++23 build & package management tool.
+#
+# This formula ships the SAME prebuilt release artifacts that upstream's
+# `install.sh` one-liner downloads (mcpp-community/mcpp → release.yml).
+#
+# Why `mcpp-m` and not `mcpp`: homebrew-core already owns the name `mcpp`
+# (Matsui's C preprocessor). Same collision as Arch, where upstream ships
+# `mcpp-bin` / `mcpp-m`. `Aliases/` maps both of those spellings here, so
+# `brew install mcpp-community/mcpp/mcpp` works too once the tap is present.
+#
+# version / url / sha256 are rewritten by scripts/update-formula.sh — the
+# bump workflow owns those three lines, so don't hand-edit them.
+class McppM < Formula
+  desc "Modern C++23 build and package management tool (module-first)"
+  homepage "https://github.com/mcpp-community/mcpp"
+  version "2026.7.30.3"
+  license "Apache-2.0"
+
+  # mcpp keeps its package index in sync over git.
+  depends_on "git"
+
+  on_macos do
+    # Upstream publishes an arm64-only macOS artifact, built with minos 14.0
+    # (release.yml asserts it). Intel Macs have no asset — build from source
+    # via `xlings install mcpp` or the install.sh one-liner instead.
+    depends_on arch: :arm64
+    depends_on macos: :sonoma
+
+    url "https://github.com/mcpp-community/mcpp/releases/download/v2026.7.30.3/mcpp-2026.7.30.3-macosx-arm64.tar.gz"
+    sha256 "1659be17b3f54c495c224179a570dd220fcfead25bbcda0c6279b20afa6a4e18"
+  end
+
+  on_linux do
+    on_intel do
+      url "https://github.com/mcpp-community/mcpp/releases/download/v2026.7.30.3/mcpp-2026.7.30.3-linux-x86_64.tar.gz"
+      sha256 "115cc537b17bfcaf5b5d13e0c7fcf9a591864cb6f18d10244e3828cfc1f8e1c4"
+    end
+    on_arm do
+      url "https://github.com/mcpp-community/mcpp/releases/download/v2026.7.30.3/mcpp-2026.7.30.3-linux-aarch64.tar.gz"
+      sha256 "aff78e9e04d0dfc09ef828b9a5aad3e1e4afff19de47b493a88bbbf803a00d14"
+    end
+  end
+
+  livecheck do
+    url :homepage
+    strategy :github_latest
+  end
+
+  def install
+    # The release tarball is a self-contained tree. Keep it whole under
+    # libexec and put a launcher on PATH — see the wrapper comment below for
+    # why a plain `bin.install` would break every write mcpp makes.
+    libexec.install "bin"
+    libexec.install "registry" if File.directory?("registry")
+
+    # mcpp WRITES at runtime: registry sandbox, BMI/metadata caches, logs and
+    # every toolchain it downloads (hundreds of MB). It resolves MCPP_HOME
+    # from the running binary's *real* path (canonical, symlinks resolved), so
+    # a bare symlink into the Cellar would make MCPP_HOME the Cellar version
+    # dir — `brew upgrade` would then silently drop every installed toolchain.
+    # Pin the two env knobs the binary honors, deferring to values the user
+    # already exported. Mirrors the Arch launcher (upstream scripts/aur).
+    (bin/"mcpp").write <<~SH
+      #!/bin/sh
+      export MCPP_HOME="${MCPP_HOME:-$HOME/.mcpp}"
+      export MCPP_VENDORED_XLINGS="${MCPP_VENDORED_XLINGS:-#{libexec}/registry/bin/xlings}"
+      exec "#{libexec}/bin/mcpp" "$@"
+    SH
+    chmod 0755, bin/"mcpp"
+
+    prefix.install "LICENSE" if File.exist?("LICENSE")
+    doc.install "README.md" if File.exist?("README.md")
+  end
+
+  def caveats
+    <<~EOS
+      mcpp keeps per-user state in ~/.mcpp (registry, caches, toolchains).
+      Override with MCPP_HOME=<dir>; remove ~/.mcpp to reset.
+
+      The first `mcpp build` downloads a toolchain (LLVM on macOS) and may
+      take a while. It is cached in ~/.mcpp and survives `brew upgrade`.
+    EOS
+  end
+
+  test do
+    assert_match version.to_s, shell_output("#{bin}/mcpp --version")
+    assert_match "Usage:", shell_output("#{bin}/mcpp --help")
+
+    # The launcher must pin MCPP_HOME outside the Cellar, or `brew upgrade`
+    # would take the user's toolchains with it. Asserted statically: the
+    # commands that would print the resolved home (`mcpp self env`) bootstrap
+    # the sandbox over the network, which has no place in a formula test.
+    launcher = (bin/"mcpp").read
+    assert_match(/MCPP_HOME="\$\{MCPP_HOME:-\$HOME\/\.mcpp\}"/, launcher)
+    assert_predicate libexec/"bin/mcpp", :executable?
+  end
+end