build: flatten esm5 sources before rollup

this is needed to update to latest rules_nodejs due to breaking change in
bazelbuild/rules_nodejs#172
It has the side-effect of correctly marking rxjs packages as side-effect-free

WORKSPACE

@@ -2,9 +2,9 @@ workspace(name = "angular")
 
 http_archive(
     name = "build_bazel_rules_nodejs",
-    url = "https://github.com/bazelbuild/rules_nodejs/archive/0.6.0.zip",
-    strip_prefix = "rules_nodejs-0.6.0",
-    sha256 = "e8a2bb5ca51fbafb244bc507bcebcae33a63d969f47413b319a8dcce032845bf",
+    url = "https://github.com/bazelbuild/rules_nodejs/archive/cd368bd71a4b04fae0eafb5c5e2c906a93772584.zip",
+    strip_prefix = "rules_nodejs-cd368bd71a4b04fae0eafb5c5e2c906a93772584",
+    sha256 = "db74c61dd8bf73cc50aed56e78b7a8ad383f5869206901506cf8d3ee27f9277f",
 )
 
 load("@build_bazel_rules_nodejs//:defs.bzl", "check_bazel_version", "node_repositories", "yarn_install")

packages/bazel/src/esm5.bzl

@@ -126,3 +126,45 @@ esm5_outputs_aspect = aspect(
         ),
     },
 )
+
+def esm5_root_dir(ctx):
+  return ctx.label.name + ".esm5"
+
+def flatten_esm5(ctx):
+  """Merge together the .esm5 folders from the dependencies.
+
+  Two different dependencies A and B may have outputs like
+  `bazel-bin/path/to/A.esm5/path/to/lib.js`
+  `bazel-bin/path/to/B.esm5/path/to/main.js`
+
+  In order to run rollup on this app, in case main.js contains `import from './lib'`
+  they need to be together in the same root directory, so if we depend on both A and B
+  we need the outputs to be
+  `bazel-bin/path/to/my_rule.esm5/path/to/lib.js`
+  `bazel-bin/path/to/my_rule.esm5/path/to/main.js`
+
+  Args:
+    ctx: the skylark rule execution context
+
+  Returns:
+    list of flattened files
+  """
+  esm5_sources = []
+  result = []
+  for dep in ctx.attr.deps:
+    if ESM5Info in dep:
+      transitive_output = dep[ESM5Info].transitive_output
+      esm5_sources.extend(transitive_output.values())
+  for f in depset(transitive = esm5_sources).to_list():
+    path = f.short_path[f.short_path.find(".esm5") + len(".esm5"):]
+    if (path.startswith("../")):
+      path = "external/" + path[3:]
+    rerooted_file = ctx.actions.declare_file("/".join([esm5_root_dir(ctx), path]))
+    result.append(rerooted_file)
+    # print("copy", f.short_path, "to", rerooted_file.short_path)
+    ctx.actions.expand_template(
+        output = rerooted_file,
+        template = f,
+        substitutions = {},
+    )
+  return result

packages/bazel/src/ng_package/ng_package.bzl

@@ -16,7 +16,7 @@ load("@build_bazel_rules_nodejs//:internal/npm_package/npm_package.bzl",
      "NPM_PACKAGE_OUTPUTS",
      "create_package")
 load("@build_bazel_rules_nodejs//:internal/node.bzl", "sources_aspect")
-load("//packages/bazel/src:esm5.bzl", "esm5_outputs_aspect", "ESM5Info")
+load("//packages/bazel/src:esm5.bzl", "esm5_outputs_aspect", "flatten_esm5", "esm5_root_dir")
 
 # TODO(alexeagle): this list is incomplete, add more as material ramps up
 WELL_KNOWN_GLOBALS = {
@@ -114,19 +114,7 @@ def _ng_package_impl(ctx):
   npm_package_directory = ctx.actions.declare_directory("%s.ng_pkg" % ctx.label.name)
 
   esm_2015_files = collect_es6_sources(ctx)
-
-  esm5_sources = depset()
-  root_dirs = []
-
-  for dep in ctx.attr.deps:
-    if ESM5Info in dep:
-      # TODO(alexeagle): we could make the module resolution in the rollup plugin
-      # faster if we kept the files grouped with their root dir. This approach just
-      # passes in both lists and requires multiple lookups (with expensive exception
-      # handling) to locate the files again.
-      transitive_output = dep[ESM5Info].transitive_output
-      root_dirs.extend(transitive_output.keys())
-      esm5_sources = depset(transitive=[esm5_sources] + transitive_output.values())
+  esm5_sources = depset(flatten_esm5(ctx))
 
   # These accumulators match the directory names where the files live in the
   # Angular package format.
@@ -190,7 +178,7 @@ def _ng_package_impl(ctx):
       umd_output = ctx.outputs.umd
       min_output = ctx.outputs.umd_min
 
-    config = write_rollup_config(ctx, [], root_dirs)
+    config = write_rollup_config(ctx, [], "/".join([ctx.bin_dir.path, ctx.label.package, esm5_root_dir(ctx)]))
 
     fesm2015.append(_rollup(ctx, config, es2015_entry_point, esm_2015_files, fesm2015_output))
     fesm5.append(_rollup(ctx, config, es5_entry_point, esm5_sources, fesm5_output))

packages/bazel/src/ng_rollup_bundle.bzl

@@ -18,11 +18,11 @@ load("@build_bazel_rules_nodejs//internal/rollup:rollup_bundle.bzl",
     "run_rollup",
     "run_uglify")
 load("@build_bazel_rules_nodejs//internal:collect_es6_sources.bzl", collect_es2015_sources = "collect_es6_sources")
-load(":esm5.bzl", "esm5_outputs_aspect", "ESM5Info")
+load(":esm5.bzl", "esm5_outputs_aspect", "flatten_esm5", "esm5_root_dir")
 
-PACKAGES=["core", "common"]
+PACKAGES=["packages/core/src", "packages/common/src", "external/rxjs"]
 PLUGIN_CONFIG="{sideEffectFreeModules: [\n%s]}" % ",\n".join(
-    ["        'packages/{0}/{0}.esm5'".format(p) for p in PACKAGES])
+    ["        '.esm5/{0}'".format(p) for p in PACKAGES])
 BO_ROLLUP="angular_devkit/packages/angular_devkit/build_optimizer/src/build-optimizer/rollup-plugin.js"
 BO_PLUGIN="require('%s').default(%s)" % (BO_ROLLUP, PLUGIN_CONFIG)
 
@@ -41,21 +41,10 @@ def _ng_rollup_bundle(ctx):
   esm2015_rollup_config = write_rollup_config(ctx, filename = "_%s.rollup_es6.conf.js")
   run_rollup(ctx, collect_es2015_sources(ctx), esm2015_rollup_config, ctx.outputs.build_es6)
 
-  esm5_sources = []
-  root_dirs = []
+  esm5_sources = flatten_esm5(ctx)
 
-  for dep in ctx.attr.deps:
-    if ESM5Info in dep:
-      # TODO(alexeagle): we could make the module resolution in the rollup plugin
-      # faster if we kept the files grouped with their root dir. This approach just
-      # passes in both lists and requires multiple lookups (with expensive exception
-      # handling) to locate the files again.
-      transitive_output = dep[ESM5Info].transitive_output
-      root_dirs.extend(transitive_output.keys())
-      esm5_sources.extend(transitive_output.values())
-
-  rollup_config = write_rollup_config(ctx, [BO_PLUGIN], root_dirs)
-  run_rollup(ctx, depset(transitive = esm5_sources).to_list(), rollup_config, ctx.outputs.build_es5)
+  rollup_config = write_rollup_config(ctx, [BO_PLUGIN], "/".join([ctx.bin_dir.path, ctx.label.package, esm5_root_dir(ctx)]))
+  run_rollup(ctx, esm5_sources, rollup_config, ctx.outputs.build_es5)
 
   run_uglify(ctx, ctx.outputs.build_es5, ctx.outputs.build_es5_min,
       comments = False)