fstar: add extract.sh script and fstar-extract.yml GHA workflow for Meta-F* extraction

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Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

.github/workflows/fstar-extract.yml

@@ -0,0 +1,93 @@
+name: "F* Meta Extraction"
+
+# Run the Meta-F* reflection-based extraction that generates C++ rewrite rules
+# from the F* lemmas in fstar/FPARewriterRules.fst.
+#
+# The extraction is performed by fstar/RewriteCodeGen.fst which uses
+# FStar.Tactics.V2 and FStar.Reflection.V2 to inspect the lemma types
+# and emit C++ if-blocks that implement the corresponding rewrite rules.
+#
+# The generated C++ is printed to the job log and uploaded as an artifact.
+
+on:
+  push:
+    paths:
+      - "fstar/**.fst"
+      - "fstar/extract.sh"
+      - ".github/workflows/fstar-extract.yml"
+  pull_request:
+    paths:
+      - "fstar/**.fst"
+      - "fstar/extract.sh"
+      - ".github/workflows/fstar-extract.yml"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  fstar-extract:
+    name: "Meta-F* rewrite rule extraction"
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6.0.2
+
+      # -----------------------------------------------------------------------
+      # Install F*
+      #
+      # We download the pre-built Linux binary from the F* GitHub releases.
+      # The version is pinned to match what the README recommends.
+      # If the pinned release is unavailable the step fails clearly.
+      # -----------------------------------------------------------------------
+      - name: Install F*
+        env:
+          FSTAR_VERSION: "2024.09.05"
+        run: |
+          ARCHIVE="fstar_v${FSTAR_VERSION}_Linux_x86_64.tar.gz"
+          URL="https://github.com/FStarLang/FStar/releases/download/v${FSTAR_VERSION}/${ARCHIVE}"
+          echo "Downloading F* ${FSTAR_VERSION} from ${URL}" >&2
+          curl -fsSL -o "/tmp/${ARCHIVE}" "${URL}"
+          mkdir -p "$HOME/fstar"
+          tar -xzf "/tmp/${ARCHIVE}" -C "$HOME/fstar" --strip-components=1
+          echo "$HOME/fstar/bin" >> "$GITHUB_PATH"
+
+      - name: Verify F* installation
+        run: fstar.exe --version
+
+      # -----------------------------------------------------------------------
+      # Run the Meta-F* extraction
+      #
+      # RewriteCodeGen.fst contains run_tactic calls that print generated C++
+      # to stdout during typechecking.  We capture that output, show it in the
+      # log, and upload it as an artifact for inspection.
+      # -----------------------------------------------------------------------
+      - name: Extract C++ rewrite rules via Meta-F*
+        working-directory: fstar
+        run: |
+          chmod +x extract.sh
+          echo "--- generated C++ rules ---"
+          ./extract.sh | tee extracted_rules.txt
+          echo "--- end of generated rules ---"
+
+      - name: Show extracted rules
+        working-directory: fstar
+        run: |
+          echo "Lines of generated C++ output:"
+          wc -l extracted_rules.txt
+          echo ""
+          echo "Full content:"
+          cat extracted_rules.txt
+
+      # -----------------------------------------------------------------------
+      # Upload the extracted rules as a build artifact so reviewers can
+      # inspect the generated C++ without re-running the workflow.
+      # -----------------------------------------------------------------------
+      - name: Upload extracted rules artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: fstar-extracted-cpp-rules
+          path: fstar/extracted_rules.txt
+          if-no-files-found: error

fstar/README.md

@@ -211,8 +211,14 @@ fstar.exe --include . IEEE754.fst FPARewriterRules.fst
 
 ### Running the Meta-F* extraction
 
-To run the reflection-based C++ code extraction and print the generated
+The convenience script `extract.sh` runs the extraction and prints the
-rewrite rules to stdout:
+generated C++ rules to stdout:
+
+```sh
+cd fstar && ./extract.sh
+```
+
+Or invoke F* directly:
 
 ```sh
 fstar.exe --include . IEEE754.fst FPARewriterRules.fst RewriteCodeGen.fst
@@ -220,14 +226,21 @@ fstar.exe --include . IEEE754.fst FPARewriterRules.fst RewriteCodeGen.fst
 
 This type-checks all three files and executes the `run_tactic` calls in
 `RewriteCodeGen.fst`, printing the generated C++ for each ite-pushthrough
-lemma.  Redirect stdout to a file to capture the output:
+lemma.  To capture the output to a file:
 
 ```sh
-fstar.exe --include . IEEE754.fst FPARewriterRules.fst RewriteCodeGen.fst \
+./extract.sh > extracted_rules.txt
-  2>/dev/null
 ```
 
-F\* 2024.09.05 or later is recommended.  The files have no external
+### Continuous integration
+
+The GitHub Actions workflow `.github/workflows/fstar-extract.yml` runs
+the extraction automatically on every push or pull request that touches
+the `fstar/` directory.  It installs the F* binary, runs `extract.sh`,
+and uploads the generated C++ as a downloadable artifact
+`fstar-extracted-cpp-rules` for inspection.
+
+F\* 2024.09.05 or later is required.  The files have no external
 dependencies beyond the F\* standard library prelude.
 
 Because all IEEE 754 semantics are encoded as `assume val` axioms, the

fstar/extract.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+# extract.sh
+#
+# Run the Meta-F* reflection-based extraction to generate C++ rewrite rules
+# from the F* lemmas in this directory.
+#
+# Usage (from the fstar/ directory):
+#   ./extract.sh
+#
+# Usage (from the repo root):
+#   fstar/extract.sh
+#
+# Output:
+#   Prints the generated C++ rules to stdout.
+#   Exits non-zero if F* typechecking or tactic execution fails.
+#
+# Requirements:
+#   fstar.exe on PATH (F* 2024.09.05 or later recommended).
+#   The three source files must be present:
+#     IEEE754.fst, FPARewriterRules.fst, RewriteCodeGen.fst
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+if ! command -v fstar.exe &>/dev/null; then
+    echo "ERROR: fstar.exe not found on PATH." >&2
+    echo "Install F* 2024.09.05+ from https://github.com/FStarLang/FStar/releases" >&2
+    exit 1
+fi
+
+echo "=== F* version ===" >&2
+fstar.exe --version >&2
+
+echo "" >&2
+echo "=== Running Meta-F* extraction ===" >&2
+
+# F* writes tactic print() output to stdout.
+# Verification progress and errors go to stderr.
+fstar.exe --include . \
+    IEEE754.fst \
+    FPARewriterRules.fst \
+    RewriteCodeGen.fst
+
+echo "" >&2
+echo "=== Extraction complete ===" >&2