Bootstrap in stages

This requires the `bootstrap/1` tag, which we have to fetch explicitly
on the test runners (see
actions/checkout#701).

.github/workflows/graphene_tests.yml

@@ -38,6 +38,8 @@ jobs:
         sudo ./llvm.sh ${{ matrix.llvm-version }}
         sudo apt-get install -y llvm-${{ matrix.llvm-version }}-runtime
     - name: Bootstrap the parser
-      run: ./bootstrap.sh
+      run: |
+        git fetch --tags origin
+        ./bootstrap.sh
     - name: Run tests
       run: python tests/run_tests.py

bootstrap.sh

@@ -1,4 +1,19 @@
 #!/usr/bin/env bash
 
-# Atm this is easy... it becomes harder once we remove lark
+set -ex
+
+# Attempt to get the current location. Prefer a branch name if available,
+# otherwise fall back to the current commit's hash if we are in "detached HEAD"
+# state.
+git_location=$(git branch --show)
+if [[ "$git_location" == "" ]]; then
+    git_location=$(git rev-parse HEAD)
+fi
+
+# Stage 1; last commit where the Lark parser can parse the native parser.
+git checkout bootstrap/1
 ./glang ./parser/parser.c3 -o ./parser/parser --bootstrap -O3
+
+# Stage 2; build native parser at current commit
+git checkout "$git_location"
+./glang ./parser/parser.c3 -o ./parser/parser -O3