feat: jest coverage output

e2e/case6.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -o errexit -o nounset -o pipefail
+
+# Case 6: generate a coverage report
+bazel coverage //jest/tests:case6 --instrument_test_targets
+
+COVERAGE_FILE="bazel-testlogs/jest/tests/case6/coverage.dat"
+
+if [ ! -f "$COVERAGE_FILE" ]; then
+    echo "Missing coverage file $COVERAGE_FILE"
+    exit 1
+fi
+
+if ! grep -q "foobar" "$COVERAGE_FILE"; then
+    echo "Coverage file does not contain coverage for foobar function"
+    exit 1
+fi

jest/private/BUILD.bazel

@@ -12,3 +12,9 @@ bzl_library(
     srcs = ["jest_test.bzl"],
     visibility = ["//jest:__subpackages__"],
 )
+
+sh_binary(
+    name = "noop",
+    srcs = ["noop.sh"],
+    visibility = ["//visibility:public"],
+)

jest/private/jest_config_template.mjs

@@ -1,10 +1,11 @@
 // jest.config.js template for jest_test rule
-import { existsSync } from "fs";
+import { existsSync, readFileSync } from "fs";
 import * as path from "path";
 
 // isTest indicates if this is a test target or if this is a binary target generating reference output snapshots for the snapshot updater target
 const isTest = !!process.env.TEST_TARGET;
 const updateSnapshots = process.env.JEST_TEST__UPDATE_SNAPSHOTS;
+const coverageEnabled = !!"{{COVERAGE_ENABLED}}";
 const autoConfReporters = !!"{{AUTO_CONF_REPORTERS}}";
 const autoConfTestSequencer = !!"{{AUTO_CONF_TEST_SEQUENCER}}";
 const userConfigShortPath = "{{USER_CONFIG_SHORT_PATH}}";
@@ -138,6 +139,26 @@ if (updateSnapshots) {
   config.snapshotResolver = bazelSnapshotResolverPath;
 }
 
+if (coverageEnabled) {
+  config.collectCoverage = true;
+  config.coverageDirectory = path.dirname(process.env.COVERAGE_OUTPUT_FILE);
+  config.coverageReporters = [
+    "text",
+    ["lcovonly", { file: path.basename(process.env.COVERAGE_OUTPUT_FILE) }],
+  ];
+
+  // Glob pattern paths for which files to cover must be relative to the user's
+  // jest config file.
+  const userConfigDir = path.dirname(_resolveRunfilesPath(userConfigShortPath));
+
+  // Only generate coverage for files declared in the COVERAGE_MANIFEST
+  config.collectCoverageFrom = readFileSync(process.env.COVERAGE_MANIFEST)
+    .toString('utf8')
+    .split('\n')
+    .filter((f) => f != '')
+    .map(f => path.relative(userConfigDir, f));
+}
+
 if (process.env.JS_BINARY__LOG_DEBUG) {
   console.error(
     "DEBUG: aspect_rules_jest[jest_test]: config:",

jest/private/jest_test.bzl

@@ -45,9 +45,17 @@ _attrs = dicts.add(js_binary_lib.attrs, {
         allow_single_file = True,
         default = Label("//jest/private:jest_config_template.mjs"),
     ),
+    # Earlier versions of Bazel expect this attribute to be present.
+    # We use a no-op because jest itself generates the coverage.
+    "_lcov_merger": attr.label(
+        executable = True,
+        default = Label("//jest/private:noop"),
+        cfg = "exec",
+    ),
 })
 
 def _impl(ctx):
+    providers = []
     generated_config = ctx.actions.declare_file("%s__jest.config.mjs" % ctx.label.name)
     user_config = copy_file_to_bin_action(ctx, ctx.file.config) if ctx.attr.config else None
 
@@ -60,6 +68,7 @@ def _impl(ctx):
             "{{BAZEL_SEQUENCER_SHORT_PATH}}": ctx.file.bazel_sequencer.short_path,
             "{{BAZEL_SNAPSHOT_REPORTER_SHORT_PATH}}": ctx.file.bazel_snapshot_reporter.short_path,
             "{{BAZEL_SNAPSHOT_RESOLVER_SHORT_PATH}}": ctx.file.bazel_snapshot_resolver.short_path,
+            "{{COVERAGE_ENABLED}}": "1" if ctx.coverage_instrumented else "",
             "{{JUNIT_REPORTER_SHORT_PATH}}": "../{jest_repository}/node_modules/jest-junit/index.js".format(jest_repository = ctx.attr.jest_repository),
             "{{USER_CONFIG_SHORT_PATH}}": user_config.short_path if user_config else "",
             "{{USER_CONFIG_PATH}}": user_config.path if user_config else "",
@@ -129,12 +138,28 @@ def _impl(ctx):
         for target in ctx.attr.data
     ])
 
-    return [
+    if ctx.configuration.coverage_enabled:
+        providers.append(
+            coverage_common.instrumented_files_info(
+                ctx,
+                source_attributes = ["data"],
+                extensions = [
+                    "mjs",
+                    "cjs",
+                    "js",
+                    "jsx",
+                ],
+            ),
+        )
+
+    providers.append(
         DefaultInfo(
             executable = launcher.executable,
             runfiles = runfiles,
         ),
-    ]
+    )
+
+    return providers
 
 lib = struct(
     attrs = _attrs,

jest/private/noop.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+set -o errexit -o nounset -o pipefail
+
+exit 0

jest/tests/BUILD.bazel

@@ -39,3 +39,13 @@ jest_test(
         "case5.test.js",
     ],
 )
+
+# Case 6: Coverage reporting (see e2e test)
+jest_test(
+    name = "case6",
+    config = "case6.jest.config.js",
+    data = [
+        "case6.index.js",
+        "case6.test.js",
+    ],
+)

jest/tests/case6.index.js

@@ -0,0 +1,5 @@
+function foobar() {
+  return "foobar";
+}
+
+exports.foobar = foobar;

jest/tests/case6.test.js

@@ -0,0 +1,5 @@
+const { foobar } = require("./case6.index.js");
+
+test("foobar", () => {
+  expect(foobar()).toEqual("foobar");
+});