From 6d1c2f79da9e034308c7f2cfbd16499e0cfd51f9 Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Mon, 4 Oct 2021 12:03:19 -0400
Subject: [PATCH] refactor(migrations): ensure CommonJS migrations can be
 accessed (#43657)

The `@angular/core` migrations are currently published as CommonJS and also not bundled. Schematics, of which migrations are a type, are currently required to be CommonJS modules due to the Schematics Runtime not yet supporting ESM-based schematics. To ensure that the migration files are loaded as CommonJS modules, a nested `package.json` file has been introduced within the `schematics` directory of the package to set the `type` field for all containing JavaScript files as CommonJS. Since the migrations are also not currently bundled and the `devmode` output used to build the migrations will replace all relative imports with fully-qualified module specifiers, an additional `exports` entry must be added to allow the fully-qualified module specifiers to correctly resolve. If `devmode` did not change the relative imports the additional entry would not be needed. Bundling would also remedy the situation and is the long-term path, especially once the migrations are converted to ESM. Additional followup changes should investigate bundling each migration. The additional `exports` entry should be removed if either `devmode` behavior is changed or the migrations are bundled.

PR Close #43657
---
 packages/bazel/test/ng_package/core_package.spec.ts | 3 +++
 packages/core/package.json                          | 5 +++++
 packages/core/schematics/BUILD.bazel                | 5 ++++-
 packages/core/schematics/package.json               | 3 +++
 4 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 packages/core/schematics/package.json

diff --git a/packages/bazel/test/ng_package/core_package.spec.ts b/packages/bazel/test/ng_package/core_package.spec.ts
index 71200f55334..ea19bf0fba8 100644
--- a/packages/bazel/test/ng_package/core_package.spec.ts
+++ b/packages/bazel/test/ng_package/core_package.spec.ts
@@ -72,6 +72,9 @@ describe('@angular/core ng_package', () => {
               node: './fesm2015/testing.mjs',
               default: './fesm2020/testing.mjs',
             },
+            './schematics/*': {
+              'default': './schematics/*.js',
+            },
           }
         }));
       });
diff --git a/packages/core/package.json b/packages/core/package.json
index 9ea40ad28a6..0dde09a527c 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -7,6 +7,11 @@
   "engines": {
     "node": "^12.14.1 || >=14.0.0"
   },
+  "exports": {
+    "./schematics/*": {
+      "default": "./schematics/*.js"
+    }
+  },
   "dependencies": {
     "tslib": "^2.3.0"
   },
diff --git a/packages/core/schematics/BUILD.bazel b/packages/core/schematics/BUILD.bazel
index 66c250a589d..a1397b8bb0a 100644
--- a/packages/core/schematics/BUILD.bazel
+++ b/packages/core/schematics/BUILD.bazel
@@ -7,7 +7,10 @@ exports_files([
 
 pkg_npm(
     name = "npm_package",
-    srcs = ["migrations.json"],
+    srcs = [
+        "migrations.json",
+        "package.json",
+    ],
     visibility = ["//packages/core:__pkg__"],
     deps = [
         "//packages/core/schematics/migrations/abstract-control-parent",
diff --git a/packages/core/schematics/package.json b/packages/core/schematics/package.json
new file mode 100644
index 00000000000..5bbefffbabe
--- /dev/null
+++ b/packages/core/schematics/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}