feat(bazel): add rule for extracting type definitions from targets (#430

)

Adds a rule that collects all direct and transitive type definitions of specified targets. The
definitons are then exposed through the `DefaultInfo` provider, allowing for easy
consumption in other rules.

This rule can be helpful if TypeScript typings are shipped along with bundled runtime code.

PR Close #430

bazel/BUILD.bazel

@@ -4,6 +4,7 @@ filegroup(
         "BUILD.bazel",
         "expand_template.bzl",
         "extract_js_module_output.bzl",
+        "extract_types.bzl",
         "//bazel/api-golden:files",
         "//bazel/benchmark:files",
         "//bazel/browsers:files",

bazel/extract_types.bzl

@@ -0,0 +1,33 @@
+load("@build_bazel_rules_nodejs//:providers.bzl", "DeclarationInfo")
+
+def _extract_types_impl(ctx):
+    """Implementation of the `extract_types` rule."""
+    depsets = []
+
+    for dep in ctx.attr.deps:
+        if DeclarationInfo in dep:
+            depsets.append(dep[DeclarationInfo].transitive_declarations)
+
+    types = depset(transitive = depsets)
+
+    return [
+        DefaultInfo(files = types),
+    ]
+
+extract_types = rule(
+    implementation = _extract_types_impl,
+    doc = """
+      Rule that collects all direct and transitive type definitions of specified targets. The
+      definitons are then exposed through the `DefaultInfo` provider, allowing for easy
+      consumption in other rules.
+
+      This rule can be helpful if TypeScript typings are shipped along with bundled runtime code.
+    """,
+    attrs = {
+        "deps": attr.label_list(
+            doc = """List of targets for which all direct and transitive type definitions
+              should be collected.""",
+            mandatory = True,
+        ),
+    },
+)