feat(typescript): ts_project is linkable

This doesn't copy a package.json file, so it has to be resolvable with just index.ts

packages/typescript/internal/ts_project.bzl

@@ -1,6 +1,7 @@
 "ts_project rule"
 
-load("@build_bazel_rules_nodejs//:providers.bzl", "DeclarationInfo", "NpmPackageInfo", "run_node")
+load("@build_bazel_rules_nodejs//:providers.bzl", "DeclarationInfo", "LinkablePackageInfo", "NpmPackageInfo", "run_node")
+load("@build_bazel_rules_nodejs//internal/linker:link_node_modules.bzl", "module_mappings_aspect")
 
 _DEFAULT_TSC = (
     # BEGIN-INTERNAL
@@ -10,6 +11,7 @@ _DEFAULT_TSC = (
 )
 
 _ATTRS = {
+    "package_name": attr.string(),
     # NB: no restriction on extensions here, because tsc sometimes adds type-check support
     # for more file kinds (like require('some.json')) and also
     # if you swap out the `compiler` attribute (like with ngtsc)
@@ -19,7 +21,10 @@ _ATTRS = {
     "extends": attr.label_list(allow_files = [".json"]),
     "tsc": attr.label(default = Label(_DEFAULT_TSC), executable = True, cfg = "host"),
     "tsconfig": attr.label(mandatory = True, allow_single_file = [".json"]),
-    "deps": attr.label_list(providers = [DeclarationInfo]),
+    "deps": attr.label_list(
+        aspects = [module_mappings_aspect],
+        providers = [DeclarationInfo],
+    ),
 }
 
 # tsc knows how to produce the following kinds of output files.
@@ -144,6 +149,14 @@ def _ts_project_impl(ctx):
             ),
         )
 
+    if ctx.attr.package_name:
+        path = "/".join([p for p in [ctx.bin_dir.path, ctx.label.workspace_root, ctx.label.package] if p])
+        providers.append(LinkablePackageInfo(
+            package_name = ctx.attr.package_name,
+            path = path,
+            files = depset(typings_outputs, transitive = [runtime_outputs]),
+        ))
+
     return providers
 
 ts_project = rule(
@@ -350,6 +363,7 @@ def ts_project_macro(
             Instructs Bazel to expect a `.tsbuildinfo` output.
         emit_declaration_only: if the `emitDeclarationOnly` bit is set in the tsconfig.
             Instructs Bazel *not* to expect `.js` or `.js.map` outputs for `.ts` sources.
+        **kwargs: undocumented additional attributes to ts_project rule wrapped by this macro
     """
 
     if srcs == None:

packages/typescript/test/ts_project/linkable/app/BUILD.bazel

@@ -0,0 +1,8 @@
+load("//packages/typescript:index.bzl", "ts_project")
+
+ts_project(
+    # This causes the linker to symlink the output directory into our execroot
+    # execroot/node_modules/@bazel/ts_project_lib ->
+    # bazel-out/[arch]/bin/packages/typescript/test/ts_project/linkable_lib
+    deps = ["//packages/typescript/test/ts_project/linkable/lib:tsconfig"],
+)

packages/typescript/test/ts_project/linkable/app/index.ts

@@ -0,0 +1,4 @@
+import {a} from '@bazel/ts_project_lib';
+import {b} from '@bazel/ts_project_lib/other';
+
+console.error(`got ${a} ${b}`);

packages/typescript/test/ts_project/linkable/app/tsconfig.json

@@ -0,0 +1 @@
+{}

packages/typescript/test/ts_project/linkable/lib/BUILD.bazel

@@ -0,0 +1,8 @@
+load("//packages/typescript:index.bzl", "ts_project")
+
+# This directory will be linked into downstream rules in node_modules/@bazel/ts_project_lib
+ts_project(
+    package_name = "@bazel/ts_project_lib",
+    declaration = True,
+    visibility = ["//packages/typescript/test:__subpackages__"],
+)

packages/typescript/test/ts_project/linkable/lib/index.ts

@@ -0,0 +1 @@
+export const a: number = 1;

packages/typescript/test/ts_project/linkable/lib/other.ts

@@ -0,0 +1 @@
+export const b: string = 'b';

packages/typescript/test/ts_project/linkable/lib/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        "declaration": true
+    }
+}