Refactor preprocessing (#770)

* Refactor preprocessing

* Refactor preprocessing

* Add tests

* Simplification

* Workflow

Author: angelhof

.github/workflows/preprocessor-tests.yaml

@@ -0,0 +1,63 @@
+name: Preprocessor Tests
+
+on:
+  pull_request:
+    types: [assigned, opened, synchronize, reopened, ready_for_review]
+    paths:
+      - preprocessor/**
+      - compiler/parser/**
+      - pa.sh
+  push:
+    branches:
+      - main
+      - future
+    paths:
+      - preprocessor/**
+      - compiler/parser/**
+      - pa.sh
+
+jobs:
+  preprocessor-tests:
+    runs-on: ubuntu-24.04
+    if: github.event.pull_request.draft == false
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libffi-dev pkg-config
+
+      - name: Install PaSh dependencies
+        run: |
+          sudo touch /.githubenv
+          sudo -E bash scripts/distro-deps.sh -o
+          sudo -E bash scripts/setup-pash.sh -o
+
+      - name: Run preprocessor tests
+        run: |
+          export PASH_TOP=$PWD
+          export PASH_TMP_PREFIX=$(mktemp -d)/
+          export PASH_BASH_VERSION="5 2 21"
+          export PYTHONPATH="$PASH_TOP/preprocessor:$PASH_TOP/compiler:$PYTHONPATH"
+
+          cd preprocessor
+          ./run_tests.sh
+
+      - name: Verify pa.sh integration
+        run: |
+          export PASH_TOP=$PWD
+          export PATH=$PATH:$PASH_TOP
+
+          # Test that preprocessing works end-to-end
+          $PASH_TOP/pa.sh -c 'echo hello'
+          $PASH_TOP/pa.sh -c 'echo hello | cat'

compiler/pash_preprocessor.py

@@ -0,0 +1,3 @@
+"""
+Shell AST utilities for the compiler.
+"""