ci: switch to mcpp build (.xlings.json pins mcpp 0.0.3) (#2)

Replaces the existing CI with a single mcpp-driven Linux job:
- `.xlings.json` declares `mcpp = { linux = "0.0.3" }`.
- `.github/workflows/ci.yml` boots xlings, runs `xlings install -y`,
  then `mcpp build` + `mcpp test` against the existing mcpp.toml.

Author: Sunrisepeak

.github/workflows/ci.yml

@@ -2,110 +2,32 @@ name: CI
 
 on:
   push:
-    branches: [main, master]
+    branches: [main]
   pull_request:
-    branches: [main, master]
-
-concurrency:
-  group: ci-${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
 
 jobs:
-  build-linux:
+  build:
     name: build + test (linux x86_64, mcpp)
-    runs-on: ubuntu-24.04
-    timeout-minutes: 30
-    env:
-      MCPP_HOME: /home/runner/.mcpp
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      # mcpp's sandbox (musl-gcc + ninja + binutils) is multi-hundred-MB;
-      # key on mcpp.toml so toolchain changes refresh the cache.
-      - name: Cache mcpp sandbox
-        uses: actions/cache@v4
-        with:
-          path: ~/.mcpp
-          key: mcpp-sandbox-${{ runner.os }}-${{ hashFiles('mcpp.toml') }}
-          restore-keys: |
-            mcpp-sandbox-${{ runner.os }}-
-
-      - name: Cache xlings
-        uses: actions/cache@v4
-        with:
-          path: ~/.xlings
-          key: xlings-${{ runner.os }}
-          restore-keys: |
-            xlings-${{ runner.os }}-
-
-      - name: Bootstrap mcpp via xlings
+      - name: Install xlings
         env:
-          XLINGS_NON_INTERACTIVE: '1'
+          XLINGS_VERSION: 0.4.25
         run: |
-          if [ ! -x "$HOME/.xlings/subos/default/bin/xlings" ]; then
-            curl -fsSL https://d2learn.org/xlings-install.sh | bash
-          fi
-          export PATH="$HOME/.xlings/subos/default/bin:$PATH"
-          xlings --version
-          xlings install mcpp -y
-          mcpp --version
-          echo "$HOME/.xlings/subos/default/bin" >> "$GITHUB_PATH"
+          tarball="xlings-${XLINGS_VERSION}-linux-x86_64.tar.gz"
+          curl -fsSL -o "/tmp/${tarball}" \
+            "https://github.com/d2learn/xlings/releases/download/v${XLINGS_VERSION}/${tarball}"
+          tar -xzf "/tmp/${tarball}" -C /tmp
+          "/tmp/xlings-${XLINGS_VERSION}-linux-x86_64/subos/default/bin/xlings" self install
+          echo "$HOME/.xlings/subos/current/bin" >> "$GITHUB_PATH"
 
-      - name: Cache target/ (build artifacts + BMIs)
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: mcpp-target-${{ runner.os }}-${{ hashFiles('src/**', 'tests/**', 'mcpp.toml') }}
-          restore-keys: |
-            mcpp-target-${{ runner.os }}-
+      - name: Install workspace tools (.xlings.json → mcpp 0.0.3)
+        run: xlings install -y
 
-      - name: Build
+      - name: Build with mcpp
         run: mcpp build
 
-      - name: Test
+      - name: Run tests
         run: mcpp test
-
-  # mcpp is Linux-x86_64 first; macOS/Windows support is still WIP, so the
-  # cross-platform xmake build keeps coverage for those targets.
-  build-macos:
-    name: build (macOS, xmake)
-    runs-on: macos-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Setup xmake
-        uses: xmake-io/github-action-setup-xmake@v1
-        with:
-          xmake-version: latest
-          package-cache: true
-
-      - name: Install LLVM 20
-        run: brew install llvm@20
-
-      - name: Build
-        run: |
-          xmake f --toolchain=llvm --sdk=/opt/homebrew/opt/llvm@20
-          xmake -y -vv
-
-  build-windows:
-    name: build + test (Windows, xmake)
-    runs-on: windows-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Setup xmake
-        uses: xmake-io/github-action-setup-xmake@v1
-        with:
-          xmake-version: latest
-          package-cache: true
-
-      - name: Build
-        run: xmake -y -vv
-
-      - name: Test
-        run: xmake run cmdline_test
-
-      - name: Run examples (smoke)
-        run: |
-          xmake run with_dispatch -- add python 3.12
-          xmake run with_dispatch -- remove foo

.xlings.json

@@ -0,0 +1,5 @@
+{
+  "workspace": {
+    "mcpp": { "linux": "0.0.3" }
+  }
+}