build: add workaround for invalid imports generation in bazel

Applies a workaround for the invalid imports generation issue
in the Bazel `ng_module` rule. Read more about this here:

https://hackmd.io/@devversion/ryCOwIKIS.

Author: devversion

WORKSPACE

@@ -42,6 +42,7 @@ yarn_install(
     # are executed in the Bazel sandbox.
     data = [
         "//:angular-tsconfig.json",
+        "//:tools/bazel/flat_module_factory_resolution.patch",
         "//:tools/bazel/postinstall-patches.js",
         "//:tools/npm/check-npm.js",
     ],

tools/bazel/flat_module_factory_resolution.patch

@@ -0,0 +1,36 @@
+diff --git node_modules/@angular/compiler/bundles/compiler.umd.js node_modules/@angular/compiler/bundles/compiler.umd.js
+index 640c42f..832f8db 100644
+--- node_modules/@angular/compiler/bundles/compiler.umd.js
++++ node_modules/@angular/compiler/bundles/compiler.umd.js
+@@ -21006,7 +21006,10 @@
+         };
+         CompileMetadataResolver.prototype.getGeneratedClass = function (dirType, name) {
+             if (dirType instanceof StaticSymbol) {
+-                return this._staticSymbolCache.get(ngfactoryFilePath(dirType.filePath), name);
++                // resolve symbol to the original file path. i.e. symbols resolved through
++                // flat module bundle will be resolved back through the "origins" field.
++                var originalPath = this._reflector.symbolResolver.getResourcePath(dirType);
++                return this._staticSymbolCache.get(ngfactoryFilePath(originalPath), name);
+             }
+             else {
+                 return this._createProxyClass(dirType, name);
+@@ -21027,7 +21030,8 @@
+         };
+         CompileMetadataResolver.prototype.getRendererType = function (dirType) {
+             if (dirType instanceof StaticSymbol) {
+-                return this._staticSymbolCache.get(ngfactoryFilePath(dirType.filePath), rendererTypeName(dirType));
++                var originalPath = this._reflector.symbolResolver.getResourcePath(dirType);
++                return this._staticSymbolCache.get(ngfactoryFilePath(originalPath), rendererTypeName(dirType));
+             }
+             else {
+                 // returning an object as proxy,
+@@ -21037,7 +21041,8 @@
+         };
+         CompileMetadataResolver.prototype.getComponentFactory = function (selector, dirType, inputs, outputs) {
+             if (dirType instanceof StaticSymbol) {
+-                return this._staticSymbolCache.get(ngfactoryFilePath(dirType.filePath), componentFactoryName(dirType));
++                var originalPath = this._reflector.symbolResolver.getResourcePath(dirType);
++                return this._staticSymbolCache.get(ngfactoryFilePath(originalPath), componentFactoryName(dirType));
+             }
+             else {
+                 var hostView = this.getHostComponentViewClass(dirType);

tools/bazel/postinstall-patches.js

@@ -10,6 +10,12 @@ const path = require('path');
 shelljs.set('-e');
 shelljs.cd(path.join(__dirname, '../..'));
 
+// Do not apply postinstall patches when running "postinstall" outside. The
+// "generate_build_file.js" file indicates that we run in Bazel managed node modules.
+if (!shelljs.test('-e', 'generate_build_file.js')) {
+  return;
+}
+
 // Workaround for https://github.com/angular/angular/issues/18810.
 shelljs.exec('ngc -p angular-tsconfig.json');
 
@@ -48,3 +54,30 @@ shelljs.sed('-i', 'var resolvedEntryPoint = null;', `
   var moduleFile = tsFiles.find(f => f.endsWith('/module.ts'));
   var resolvedEntryPoint = publicApiFile || moduleFile || null;
 `, 'node_modules/@angular/compiler-cli/src/ngtsc/entry_point/src/logic.js');
+
+// Workaround for: https://hackmd.io/MlqFp-yrSx-0mw4rD7dnQQ?both. We only want to discard
+// the metadata of files in the bazel managed node modules. That way we keep the default
+// behavior of ngc-wrapped except for dependencies between sources of the library. This makes
+// the "generateCodeForLibraries" flag more accurate in the Bazel environment where previous
+// compilations should not be treated as external libraries. Read more about this in the document.
+shelljs.sed('-i', /if \((this\.options\.generateCodeForLibraries === false)/, `
+  const fs = require('fs');
+  const hasFlatModuleBundle = fs.existsSync(filePath.replace('.d.ts', '.metadata.json'));
+  if ((filePath.includes('node_modules/') || !hasFlatModuleBundle) && $1`,
+  'node_modules/@angular/compiler-cli/src/transformers/compiler_host.js');
+shelljs.cat(path.join(__dirname, './flat_module_factory_resolution.patch')).exec('patch -p0');
+// The three replacements below ensure that metadata files can be read by NGC and
+// that metadata files are collected as Bazel action inputs.
+shelljs.sed('-i', /(const NGC_ASSETS = \/[^(]+\()([^)]*)(\).*\/;)/, '$1$2|metadata.json$3',
+  'node_modules/@angular/bazel/src/ngc-wrapped/index.js');
+shelljs.sed('-i', /^((\s*)results = depset\(dep.angular.summaries, transitive = \[results]\))$/,
+  `$1#\n$2results = depset(dep.angular.metadata, transitive = [results])`,
+  'node_modules/@angular/bazel/src/ng_module.bzl');
+shelljs.sed('-i',
+  /^((\s*)results = depset\(target.angular.summaries if hasattr\(target, "angular"\) else \[]\))$/,
+  `$1#\n$2results = depset(target.angular.metadata if hasattr(target, "angular") else [], transitive = [results])`,
+  'node_modules/@angular/bazel/src/ng_module.bzl');
+// Ensure that "metadata" of transitive dependencies can be collected.
+shelljs.sed('-i', /("metadata": outs.metadata),/,
+  `$1 + [m for dep in ctx.attr.deps if hasattr(dep, "angular") for m in dep.angular.metadata],`,
+  'node_modules/@angular/bazel/src/ng_module.bzl');

tools/defaults.bzl

@@ -43,10 +43,32 @@ def ts_library(tsconfig = None, deps = [], testonly = False, **kwargs):
         **kwargs
     )
 
-def ng_module(deps = [], tsconfig = None, module_name = None, testonly = False, **kwargs):
+def ng_module(
+        deps = [],
+        srcs = [],
+        tsconfig = None,
+        module_name = None,
+        flat_module_out_file = None,
+        testonly = False,
+        **kwargs):
     if not tsconfig:
         tsconfig = _getDefaultTsConfig(testonly)
 
+    # Targets which have a module name and are not used for tests, should
+    # have a default flat module out file named "index". This is necessary
+    # as imports to that target should go through the flat module bundle.
+    if module_name and not flat_module_out_file and not testonly:
+        flat_module_out_file = "index"
+
+    # Workaround to avoid a lot of changes to the Bazel build rules. Since
+    # for most targets the flat module out file is "index.js", we cannot
+    # include "index.ts" (if present) as source-file. This would resolve
+    # in a conflict in the metadata bundler. Once we switch to Ivy and
+    # no longer need metadata bundles, we can remove this logic.
+    if flat_module_out_file == "index":
+        if "index.ts" in srcs:
+            srcs.remove("index.ts")
+
     local_deps = [
         # Add tslib because we use import helpers for all public packages.
         "@npm//tslib",
@@ -63,8 +85,10 @@ def ng_module(deps = [], tsconfig = None, module_name = None, testonly = False,
             local_deps = local_deps + [d]
 
     _ng_module(
+        srcs = srcs,
         type_check = _ENABLE_NG_TYPE_CHECKING,
         module_name = module_name,
+        flat_module_out_file = flat_module_out_file,
         deps = local_deps,
         tsconfig = tsconfig,
         testonly = testonly,