Add script to generate fuzz coverage

.github/workflows/build.yml

@@ -129,6 +129,9 @@ jobs:
           # Will anyone be impressed by your amazing coverage? No
           # Maybe if codecov wasn't broken we wouldn't need to do this...
           bash <(curl -s https://codecov.io/bash) -f target/codecov.json -t "f421b687-4dc2-4387-ac3d-dc3b2528af57"
+      - name: Run fuzz coverage generation
+        run: |
+          ./ci/ci-fuzz.sh
 
   benchmark:
     runs-on: ubuntu-latest

ci/ci-fuzz.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+set -eox pipefail
+
+echo -e "\n\nGenerating fuzz coverage report"
+# In CI, store coverage in target directory for consistency with other artifacts
+COVERAGE_DIR="target/coverage-report"
+echo "Installing cargo-llvm-cov..."
+# Install cargo-llvm-cov if not already installed
+cargo install cargo-llvm-cov --locked
+
+echo "Cleaning up to save disk space..."
+rm -rf target/*
+echo "Disk cleanup completed"
+
+
+echo "Running fuzz coverage generation..."
+./contrib/generate_fuzz_coverage.sh --output-dir "$COVERAGE_DIR"
+echo "Coverage generation completed. Checking results..."
+
+# Upload fuzz coverage to codecov if the file exists (CI only)
+if [ -f "target/fuzz-codecov.json" ]; then
+    echo "Uploading fuzz coverage to codecov..."
+    bash <(curl -s https://codecov.io/bash) -f "target/fuzz-codecov.json" -F fuzz -t "f421b687-4dc2-4387-ac3d-dc3b2528af57"
+fi

contrib/generate_fuzz_coverage.sh

@@ -0,0 +1,88 @@
+#!/bin/bash
+set -e
+set -x
+
+# Parse command line arguments
+OUTPUT_DIR="coverage-report"
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        --output-dir)
+            OUTPUT_DIR="$2"
+            shift 2
+            ;;
+        *)
+            echo "Unknown option: $1"
+            echo "Usage: $0 [--output-dir OUTPUT_DIRECTORY]"
+            exit 1
+            ;;
+    esac
+done
+
+# Check if we're in the root directory, if so change to fuzz
+if [ -d "fuzz" ]; then
+    cd fuzz
+elif [ ! -f "Cargo.toml" ] || ! grep -q "fuzz" Cargo.toml 2>/dev/null; then
+    echo "Error: Please run this script from the rust-lightning root directory or fuzz directory"
+    exit 1
+fi
+
+# Check if test_cases directory exists and has content
+show_corpus_message=false
+if [ ! -d "test_cases" ]; then
+    show_corpus_message=true
+elif [ -z "$(find test_cases -name '*' -type f 2>/dev/null | head -1)" ]; then
+    show_corpus_message=true
+fi
+
+if [ "$show_corpus_message" = true ]; then
+    echo "Warning: No corpus found in test_cases directory."
+    echo "Generating coverage report without fuzzing corpus."
+    echo ""
+    echo "To include fuzzing corpus coverage, create test_cases directories with your corpus:"
+    echo "  mkdir -p test_cases/{target_name}"
+    echo "  cp your_corpus_directory/* test_cases/{target_name}/"
+    echo ""
+    echo "Example:"
+    echo "  mkdir -p test_cases/base32"
+    echo "  cp /path/to/your/base32_corpus/* test_cases/base32/"
+    echo ""
+fi
+
+# Create output directory if it doesn't exist
+mkdir -p "$OUTPUT_DIR"
+
+export RUSTFLAGS="--cfg=fuzzing --cfg=secp256k1_fuzz --cfg=hashes_fuzz"
+
+# dont run this command when running in CI
+if [ "$CI" != "true" ] && [ "$GITHUB_ACTIONS" != "true" ]; then
+    cargo llvm-cov --html --ignore-filename-regex "fuzz/" --output-dir "$OUTPUT_DIR"
+
+    # Check if coverage report was generated successfully
+    # The report is generated in $OUTPUT_DIR/html/index.html when using --html --output-dir
+    if [ ! -f "$OUTPUT_DIR/html/index.html" ]; then
+        echo "Error: Failed to generate coverage report at $OUTPUT_DIR/html/index.html"
+        echo "Contents of $OUTPUT_DIR:"
+        ls -la "$OUTPUT_DIR" || echo "Directory $OUTPUT_DIR does not exist"
+        if [ -d "$OUTPUT_DIR/html" ]; then
+            echo "Contents of $OUTPUT_DIR/html:"
+            ls -la "$OUTPUT_DIR/html"
+        fi
+        exit 1
+    fi
+    echo "Coverage report generated in $OUTPUT_DIR/html/index.html"
+fi
+
+# Generate codecov JSON format if running in CI environment
+if [ "$CI" = "true" ] || [ "$GITHUB_ACTIONS" = "true" ]; then
+    echo "CI environment detected, generating codecov JSON format..."
+    cargo llvm-cov --codecov --ignore-filename-regex "fuzz/" --output-path "$OUTPUT_DIR/fuzz-codecov.json"
+
+    if [ -f "$OUTPUT_DIR/fuzz-codecov.json" ] && [[ "$OUTPUT_DIR" == *"target/"* ]]; then
+        TARGET_DIR="../target"
+        cp "$OUTPUT_DIR/fuzz-codecov.json" "$TARGET_DIR/fuzz-codecov.json"
+        echo "Fuzz codecov report copied to $TARGET_DIR/fuzz-codecov.json"
+    fi
+fi
+
+
+