Add optional test coverage reports (#2517)

Co-authored-by: JesseCodeBones <xiang19890319@gmail.com>

Author: dcodeIO

.c8rc.json

@@ -0,0 +1,17 @@
+{
+  "reporter": ["html", "text"],
+  "reportsDirectory": "./coverage",
+  "src": ["src"],
+  "exclude": [
+    "std/**/*",
+    "tests/**/*",
+    "dist/**/*",
+    "bin/asinit.js",
+    "lib/**/*",
+    "scripts/**/*",
+    "src/glue/wasm/**/*",
+    "util/browser/**/*"
+  ],
+  "clean": true,
+  "exclude-after-remap": true
+}

.gitignore

@@ -9,3 +9,4 @@ raw/
 .idea
 cli/index.generated.js
 src/diagnosticMessages.generated.ts
+coverage/

package.json

@@ -70,6 +70,7 @@
     "lint": "eslint --max-warnings 0 --ext js . && eslint --max-warnings 0 --ext ts .",
     "build": "node scripts/build",
     "watch": "node scripts/build --watch",
+    "coverage": "npx c8 -- npm test",
     "test": "npm run test:parser && npm run test:compiler -- --parallel && npm run test:browser && npm run test:asconfig && npm run test:transform",
     "test:parser": "node --enable-source-maps tests/parser",
     "test:compiler": "node --enable-source-maps --no-warnings tests/compiler",

tests/README.md

@@ -116,6 +116,18 @@ Features
 
 Tests for experimental features (usually enabled via the `--enable` CLI flag) are disabled by default. To enable a feature, set the `ASC_FEATURES` environment variable to a comma-separated list of feature names (see [`features.json`](./features.json)). You can also set `ASC_FEATURES="*"` to enable all features.
 
+Coverage
+--------
+
+An optional code coverage report can be generated by running
+
+```
+$> npm install c8
+$> npm run coverage
+```
+
+Code coverage runs the tests with [c8](https://github.com/bcoe/c8) using the JS variant of the compiler. It is expected that Wasm-only branches show as untaken. Make sure to enable all (relevant) [features](#features). A convenient HTML report is generated to `coverage/`.
+
 Other
 -----
 

tests/compiler.js

@@ -492,8 +492,9 @@ function evaluateResult(failedTests, skippedTests) {
   }
 }
 
-// Run tests in parallel if requested
-if (args.parallel && coreCount > 2) {
+// Run tests in parallel if requested (except with coverage)
+const isCoverage = process.env.NODE_V8_COVERAGE != null;
+if (!isCoverage && args.parallel && coreCount > 2) {
   if (cluster.isWorker) {
     process.on("message", msg => {
       if (msg.cmd != "run") throw Error("invalid command: " + JSON.stringify(msg));