Merge haste configs if they are available

docs/troubleshooting.md

@@ -44,6 +44,10 @@ By default Jest runs tests concurrently using workers. This conflicts with Bazel
 
 By default Jest uses `jest-haste-map` to optimize and cache fs operations which must be configured to work with Bazel. `rules_jest` will automatically configure `haste` for compatibility with`rules_jest` and `rules_js`. Care must be taken with custom Jest configurations when configuring `haste`.
 
+The settings defined by `rules_jest` are `{ enableSymlinks: true }`, but if you define your own `haste:` settings (in a custom jest config), they will be _merged_ with the rules_jest defaults.
+
+_Note_: If you are importing a preset, and _it_ declares its own `haste` config, those will not be merged. This is an implementation detail of jest. The only workaround is to copy those settings into your local *jest.config.js* file.
+
 ## Pre-transpiled sources
 
 Frequently outside the Bazel ecosystem sources such as `*.ts` are transpiled on the fly using tools such as `ts-jest` or `babel-jest`. Such tools are designed for Jest and transpile to a javascript format ideal for Jest but normally not for production use.

jest/private/jest_config_template.mjs

@@ -92,7 +92,7 @@ config.cacheDirectory ||= path.join(process.env.TEST_TMPDIR, 'jest_cache');
 
 // Needed for Jest to walk the filesystem to find inputs.
 // See https://github.com/facebook/jest/pull/9351
-config.haste = { enableSymlinks: true };
+config.haste = { enableSymlinks: true, ...config.haste };
 
 // https://jestjs.io/docs/cli#--watchman. Whether to use watchman for file crawling. Defaults
 // to true. Disable using --no-watchman. Watching is ibazel's job

jest/tests/BUILD.bazel

@@ -141,3 +141,14 @@ jest_test(
     ],
     node_modules = "//:node_modules",
 )
+
+# Case 14: jest_test merges haste configs
+jest_test(
+    name = "case14",
+    config = "case14.jest.config.js",
+    data = [
+        "case14.test.js",
+        "case14-lib.foo.js",
+    ],
+    node_modules = "//:node_modules",
+)

jest/tests/case14-lib.foo.js

@@ -0,0 +1 @@
+module.exports.foo = 'foo'

jest/tests/case14.jest.config.js

@@ -0,0 +1,5 @@
+module.exports = {
+  haste: { defaultPlatform: 'foo', platforms: ['foo'] },
+  testEnvironment: "node",
+  testMatch: ["**/*.test.js"],
+}

jest/tests/case14.test.js

@@ -0,0 +1,5 @@
+const {foo} = require('./case14-lib');
+
+test("it should work", () => {
+  expect(foo).toBe('foo');
+});