Add code coverage tooling (bisect_ppx)

.github/workflows/coverage.yml

@@ -0,0 +1,75 @@
+name: Coverage
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+concurrency:
+  group: coverage-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+env:
+  OCAMLRUNPARAM: b
+
+jobs:
+  coverage:
+    runs-on: ubuntu-24.04-arm
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Use Node.js
+        uses: actions/setup-node@v6
+        with:
+          cache: yarn
+          node-version-file: .nvmrc
+
+      - name: Install npm packages
+        run: yarn install
+
+      - name: Install system dependencies
+        uses: awalsh128/cache-apt-pkgs-action@v1.4.3
+        with:
+          packages: bubblewrap darcs g++-multilib gcc-multilib mercurial musl-tools rsync cmake
+          version: v4
+
+      - name: Determine Rust toolchain version
+        id: rust-version
+        run: |
+          version="$(awk -F '"' '/^rust-version[[:space:]]*=/ { print $2; exit }' rewatch/Cargo.toml)"
+          echo "version=${version}" >> "$GITHUB_OUTPUT"
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ steps.rust-version.outputs.version }}
+          components: clippy, rustfmt
+
+      - name: Build rewatch
+        run: cargo build --manifest-path rewatch/Cargo.toml --release
+
+      - name: Copy rewatch binary
+        run: |
+          cp rewatch/target/release/rescript rescript
+          ./scripts/copyExes.js --rewatch
+
+      - name: Use OCaml
+        uses: ocaml/setup-ocaml@v3.6.0
+        with:
+          ocaml-compiler: 5.3.0
+          opam-pin: false
+
+      - name: Install OPAM dependencies (incl. bisect_ppx)
+        run: opam install . --deps-only --with-test --with-dev-setup
+
+      - name: Run coverage
+        run: opam exec -- make coverage
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          files: _coverage/coverage.json
+          fail_ci_if_error: false
+          token: ${{ secrets.CODECOV_TOKEN }}

.gitignore

@@ -47,6 +47,8 @@ _build_playground
 node_modules
 *.dump
 coverage
+_coverage/
+bisect*.coverage
 
 lib/ocaml
 tests/build_tests/*/lib/

.ocamlformat-ignore

@@ -1,18 +1,4 @@
 compiler/js_parser/**
-compiler/ml/cmt_format.ml
-compiler/core/js_name_of_module_id.ml
-compiler/core/js_pass_debug.ml
-compiler/core/lam_util.ml
-compiler/core/lam_compile_main.ml
-compiler/ext/bs_hash_stubs.ml
-compiler/ext/js_reserved_map.ml
-compiler/ext/ext_string.ml
-compiler/ext/ext_string.mli
-compiler/ext/ext_sys.ml
-compiler/ext/hash.cppo.ml
-compiler/ext/hash_set.cppo.ml
-compiler/ext/map.cppo.ml
-compiler/ext/ordered_hash_map.cppo.ml
-compiler/ext/set.cppo.ml
-compiler/ext/vec.cppo.ml
+**/*.cppo.ml
+**/*.cppo.mli
 compiler/syntax/compiler-libs-406/*

Makefile

@@ -217,6 +217,87 @@ format: | $(YARN_INSTALL_STAMP)
 checkformat: | $(YARN_INSTALL_STAMP)
 	./scripts/format_check.sh
 
+# Coverage (bisect_ppx)
+#
+# Requires the `bisect_ppx` opam package (>= 2.8.0) in your switch:
+#   opam install bisect_ppx
+# or pull it in via the rescript dev-setup deps:
+#   opam install . --deps-only --with-dev-setup
+#
+# Quick start:
+#   make coverage         # run full test suite, generate report
+#   make clean-coverage   # remove coverage artifacts
+#
+# Outputs (under _coverage/):
+#   html/index.html  — human-browsable line-level report
+#   coverage.json    — Coveralls-format JSON, queryable with jq:
+#                      { source_files: [{ name, coverage: [null|N, ...] }] }
+#                      null = not instrumented, 0 = uncovered, N > 0 = hit count
+#                      e.g. uncovered line numbers in one file:
+#                      jq -r --arg f compiler/ml/typecore.ml \
+#                        '.source_files[] | select(.name==$f) | .coverage
+#                         | to_entries[] | select(.value==0) | (.key+1)' \
+#                        _coverage/coverage.json
+
+COVERAGE_DIR := _coverage
+COVERAGE_FILES_DIR := $(COVERAGE_DIR)/files
+COVERAGE_HTML_DIR := $(COVERAGE_DIR)/html
+COVERAGE_JSON := $(COVERAGE_DIR)/coverage.json
+COVERAGE_BISECT_PREFIX := $(abspath $(COVERAGE_FILES_DIR))/bisect
+
+# Re-builds the toolchain with bisect_ppx instrumentation and swaps the
+# instrumented binaries into BIN_DIR so any test runner that shells out to
+# `bsc` produces .coverage files.
+.PHONY: coverage-build
+coverage-build: | $(YARN_INSTALL_STAMP)
+	dune build --instrument-with bisect_ppx
+	@$(foreach bin,$(COMPILER_DUNE_BINS),touch $(bin);)
+	@$(foreach bin,$(COMPILER_BIN_NAMES), \
+		cp $(DUNE_BIN_DIR)/$(bin)$(PLATFORM_EXE_EXT) $(BIN_DIR)/$(bin).exe && \
+		chmod 755 $(BIN_DIR)/$(bin).exe;)
+
+.PHONY: coverage-prepare
+coverage-prepare: clean-coverage coverage-build
+	mkdir -p $(COVERAGE_FILES_DIR)
+
+# Build the runtime with the instrumented bsc so subsequent test runs have
+# a fresh stdlib. Coverage from the runtime build is discarded so reports
+# only reflect what the tests exercised.
+.PHONY: coverage-lib
+coverage-lib: coverage-prepare
+	BISECT_FILE=$(COVERAGE_BISECT_PREFIX)-discard BISECT_SILENT=YES \
+		yarn workspace @rescript/runtime build
+	rm -f $(COVERAGE_BISECT_PREFIX)-discard*.coverage
+
+.PHONY: coverage-run
+coverage-run: coverage-lib
+	BISECT_FILE=$(COVERAGE_BISECT_PREFIX) BISECT_SILENT=YES \
+		node scripts/test.js -all
+
+.PHONY: coverage-report
+coverage-report:
+	bisect-ppx-report html \
+		--coverage-path $(COVERAGE_FILES_DIR) \
+		--ignore-missing-files \
+		-o $(COVERAGE_HTML_DIR)
+	bisect-ppx-report coveralls \
+		--coverage-path $(COVERAGE_FILES_DIR) \
+		--ignore-missing-files \
+		$(COVERAGE_JSON)
+	bisect-ppx-report summary \
+		--coverage-path $(COVERAGE_FILES_DIR)
+	@echo ""
+	@echo "HTML report: $(COVERAGE_HTML_DIR)/index.html"
+	@echo "JSON data:   $(COVERAGE_JSON)"
+
+.PHONY: coverage
+coverage: coverage-run coverage-report
+
+.PHONY: clean-coverage
+clean-coverage:
+	rm -rf $(COVERAGE_DIR)
+	find . -name 'bisect*.coverage' -not -path './_build/*' -delete
+
 # Clean
 
 clean-gentype:
@@ -225,7 +306,7 @@ clean-gentype:
 
 clean-tests: clean-gentype
 
-clean: clean-lib clean-compiler clean-rewatch
+clean: clean-lib clean-compiler clean-rewatch clean-coverage
 
 dev-container:
 	docker build -t rescript-dev-container docker

analysis/bin/dune

@@ -8,4 +8,6 @@
  (package analysis)
  (modes byte exe)
  (name main)
+ (instrumentation
+  (backend bisect_ppx))
  (libraries analysis))

analysis/src/dune

@@ -1,5 +1,7 @@
 (library
  (name analysis)
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (-w "+6+26+27+32+33+39"))
  (libraries unix str ext ml jsonlib syntax reanalyze))

codecov.yml

@@ -0,0 +1,20 @@
+coverage:
+  status:
+    project:
+      default:
+        informational: true
+        threshold: 0.5%
+    patch:
+      default:
+        informational: true
+        threshold: 0.5%
+
+comment:
+  layout: "diff, files"
+  require_changes: true
+  require_base: false
+  require_head: true
+  behavior: default
+
+github_checks:
+  annotations: false

compiler/bsc/dune

@@ -7,6 +7,8 @@
  (name rescript_compiler_main)
  (public_name bsc)
  (package rescript)
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-9-30-40-41-42-48-70))
  (libraries common core depends flow_parser gentype syntax))

compiler/common/dune

@@ -1,9 +1,8 @@
 (library
  (name common)
  (wrapped false)
- (preprocess
-  (action
-   (run %{bin:cppo} %{env:CPPO_FLAGS=} %{input-file})))
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-9-40-42))
  (libraries syntax))

compiler/core/dune

@@ -1,9 +1,32 @@
 (library
  (name core)
  (wrapped false)
- (preprocess
-  (action
-   (run %{bin:cppo} %{env:CPPO_FLAGS=} %{input-file})))
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-9-27-30-40-41-42-48-70))
  (libraries depends ext flow_parser frontend gentype))
+
+(rule
+ (target js_name_of_module_id.ml)
+ (deps js_name_of_module_id.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target js_pass_debug.ml)
+ (deps js_pass_debug.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target lam_compile_main.ml)
+ (deps lam_compile_main.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target lam_util.ml)
+ (deps lam_util.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))

compiler/depends/dune

@@ -1,6 +1,8 @@
 (library
  (name depends)
  (wrapped false)
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-40-42))
  (libraries common))

compiler/ext/dune

@@ -1,20 +1,51 @@
 (library
  (name ext)
  (wrapped false)
- (preprocess
-  (action
-   (run
-    %{bin:cppo}
-    -V
-    OCAML:%{ocaml_version}
-    %{env:CPPO_FLAGS=}
-    %{input-file})))
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-42-40-9-48-70))
  (foreign_stubs
   (language c)
   (names ext_basic_hash_stubs)))
 
+(rule
+ (target bs_hash_stubs.ml)
+ (deps bs_hash_stubs.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target js_reserved_map.ml)
+ (deps js_reserved_map.cppo.ml)
+ (action
+  (run
+   %{bin:cppo}
+   -V
+   OCAML:%{ocaml_version}
+   %{env:CPPO_FLAGS=}
+   %{deps}
+   -o
+   %{target})))
+
+(rule
+ (target ext_sys.ml)
+ (deps ext_sys.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target ext_string.ml)
+ (deps ext_string.cppo.ml)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
+(rule
+ (target ext_string.mli)
+ (deps ext_string.cppo.mli)
+ (action
+  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+
 (rule
  (targets hash_set_string.ml)
  (deps hash_set.cppo.ml)

compiler/frontend/dune

@@ -1,6 +1,8 @@
 (library
  (name frontend)
  (wrapped false)
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-9-40-42-70))
  (libraries common ml))

compiler/gentype/dune

@@ -1,6 +1,8 @@
 (library
  (name gentype)
  (wrapped false)
+ (instrumentation
+  (backend bisect_ppx))
  (flags
   (:standard -w +a-4-9-40-41-42-48-70))
  (libraries ml))