fix(builtin): fix regression in 1.6.0 in linker linking root package when under runfiles

Resolves #1823 which had a repro https://github.com/purkhusid/ts-jest-repro.

NB: The repo uses ts_library devmode UMD output so the relative require in the source code will be transformed to an absolute require which will include the workspace name.

In 1.5.0:

```
.../sandbox/darwin-sandbox/23/execroot/jest_repro/bazel-out/darwin-fastbuild/bin/test.sh.runfiles/jest_repro/lib.test.js

const lib_1 = require("jest_repro/lib");
```

works as it finds

```
.../sandbox/darwin-sandbox/23/execroot/jest_repro/bazel-out/darwin-fastbuild/bin/test.sh.runfiles/jest_repro/node_modules/jest_repro/lib.js
```

where `test.sh.runfiles/jest_repro/node_modules/jest_repro` is a symlink to the root of the output tree setup by the linker:

```
lrwxr-xr-x  1 greg  wheel  165 29 Apr 05:56 .../sandbox/darwin-sandbox/6/execroot/jest_repro/bazel-out/darwin-fastbuild/bin/test.sh.runfiles/jest_repro/node_modules/jest_repro -> .../sandbox/darwin-sandbox/6/execroot/jest_repro/bazel-out/darwin-fastbuild/bin/test.sh.runfiles/jest_repro
```

In 1.6.0:

Bug introduced in #1850 (thanks for tracking down the culprit @alexeagle) where the root symlink is not created properly when under runfiles (such as a jest_test context).

Fix is:

```
          let runfilesPath = modulePath;
          if (runfilesPath.startsWith(`${bin}/`)) {
            runfilesPath = runfilesPath.slice(bin.length + 1);
+          } else if (runfilesPath === bin) {
+            runfilesPath = '';
          }
```

in `link_node_modules.ts`.

NB: This root workspace symlink will be removed in 2.0 as it causes other unrelated issues. PR for that change is in progress #1797. In 2.0, we recommend either using the prodmode esm output of ts_library for jest_test or switching to ts_project where the output flavor is controlled by your tsconfig. An example of using ts_library esm output of ts_library (output_group 'es6_sources') is `under /internal/linker/test/issue_1823_use_ts_library_esm`. It require babel-jest to transform the esm to commonjs. Alternately, you can control the 'es5_sources' module format of ts_library with the `devmode_module` but this can lead to other issues such as the output no longer being compatible with ts_devserver and karma_web_test which require named-UMD or named-AMD.

Author: gregmagolan

internal/linker/index.js

@@ -372,6 +372,9 @@ function main(args, runfiles) {
                             if (runfilesPath.startsWith(`${bin}/`)) {
                                 runfilesPath = runfilesPath.slice(bin.length + 1);
                             }
+                            else if (runfilesPath === bin) {
+                                runfilesPath = '';
+                            }
                             const externalPrefix = 'external/';
                             if (runfilesPath.startsWith(externalPrefix)) {
                                 runfilesPath = runfilesPath.slice(externalPrefix.length);

internal/linker/link_node_modules.ts

@@ -601,6 +601,8 @@ export async function main(args: string[], runfiles: Runfiles) {
           let runfilesPath = modulePath;
           if (runfilesPath.startsWith(`${bin}/`)) {
             runfilesPath = runfilesPath.slice(bin.length + 1);
+          } else if (runfilesPath === bin) {
+            runfilesPath = '';
           }
           const externalPrefix = 'external/';
           if (runfilesPath.startsWith(externalPrefix)) {

internal/linker/test/issue_1823/BUILD.bazel

@@ -0,0 +1,22 @@
+load("@npm_bazel_typescript//:index.bzl", "ts_library")
+load(":ts_jest_test.bzl", "ts_jest_test")
+
+ts_library(
+    name = "lib",
+    srcs = [
+        "lib.ts",
+    ],
+    deps = [
+    ],
+)
+
+ts_jest_test(
+    name = "test",
+    srcs = [
+        "lib.test.ts",
+    ],
+    jest_config = "jest.config.js",
+    deps = [
+        ":lib",
+    ],
+)

internal/linker/test/issue_1823/jest.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  testEnvironment: 'node',
+};

internal/linker/test/issue_1823/lib.test.ts

@@ -0,0 +1,7 @@
+import {doStuff} from './lib';
+
+describe('doStuff', () => {
+  it('should do some stuff', () => {
+    expect(doStuff('boom')).toContain('boom');
+  });
+});

internal/linker/test/issue_1823/lib.ts

@@ -0,0 +1,3 @@
+export function doStuff(a: string): string {
+  return a
+}

internal/linker/test/issue_1823/ts_jest_test.bzl

@@ -0,0 +1,35 @@
+"""Simple macro around jest_test"""
+
+load("@npm//jest-cli:index.bzl", _jest_test = "jest_test")
+load("@npm_bazel_typescript//:index.bzl", "ts_library")
+
+def ts_jest_test(name, srcs, jest_config, deps = [], data = [], **kwargs):
+    """A macro around the autogenerated jest_test rule that takes typescript sources
+
+Uses ts_library devmode UMD output"""
+
+    ts_library(
+        name = "%s_ts" % name,
+        srcs = srcs,
+        data = data,
+        deps = deps + ["@npm//@types/jest"],
+    )
+    native.filegroup(
+        name = "%s_umd" % name,
+        srcs = [":%s_ts" % name],
+        output_group = "es5_sources",
+    )
+
+    args = [
+        "--no-cache",
+        "--no-watchman",
+        "--ci",
+    ]
+    args.extend(["--config", "$(rootpath %s)" % jest_config])
+
+    _jest_test(
+        name = name,
+        data = [jest_config, ":%s_umd" % name] + deps + data,
+        args = args,
+        **kwargs
+    )

internal/linker/test/issue_1823_use_ts_library_esm/.babelrc

@@ -0,0 +1,12 @@
+{
+  "presets": [
+    [
+      "@babel/preset-env",
+      {
+        "targets": {
+          "node": "current",
+        },
+      },
+    ],
+  ]
+}

internal/linker/test/issue_1823_use_ts_library_esm/BUILD.bazel

@@ -0,0 +1,31 @@
+load("@npm_bazel_typescript//:index.bzl", "ts_library")
+load(":ts_jest_test.bzl", "ts_jest_test")
+
+ts_library(
+    name = "lib",
+    srcs = [
+        "lib.ts",
+    ],
+    # NB: hacky hidden configuration setting so that es6_sources does not include tsickle
+    #     .externs.js outputs
+    runtime = "nodejs",
+    deps = [
+        "@npm//@types/node",
+    ],
+)
+
+ts_jest_test(
+    name = "test",
+    srcs = [
+        "lib.test.ts",
+    ],
+    data = [
+        ".babelrc",
+    ],
+    jest_config = "jest.config.js",
+    deps = [
+        ":lib",
+        "@npm//@babel/preset-env",
+        "@npm//babel-jest",
+    ],
+)

internal/linker/test/issue_1823_use_ts_library_esm/jest.config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  testEnvironment: 'node',
+  transform: {'^.+\\.mjs?$': 'babel-jest'},
+  testMatch: ['**/?(*.)(spec|test).?(m)js?(x)'],
+  moduleFileExtensions: ['js', 'mjs'],
+};