Add //tools:erlang_ls_files that generates a tree for Erlang LS

in the layout Erlang LS expects

deps/rabbitmq_amqp1_0/BUILD.bazel

@@ -80,12 +80,12 @@ suites = [
         PACKAGE,
         name = "command_SUITE",
         size = "medium",
-        deps = [
-            "//deps/amqp10_common:erlang_app",
-        ],
         runtime_deps = [
             "//deps/amqp10_client:erlang_app",
         ],
+        deps = [
+            "//deps/amqp10_common:erlang_app",
+        ],
     ),
     rabbitmq_integration_suite(
         PACKAGE,

tools/BUILD.bazel

@@ -1,4 +1,12 @@
-load(":erlang_ls.bzl", "erlang_ls_config")
+load("//:rabbitmq.bzl", "all_plugins")
+load(":erlang_ls.bzl", "erlang_ls_config", "erlang_ls_tree")
+
+erlang_ls_tree(
+    name = "erlang_ls_files",
+    apps = all_plugins(
+        rabbitmq_workspace = "",
+    ),
+)
 
 erlang_ls_config(
     name = "erlang_ls.config",

tools/erlang_ls.bzl

@@ -1,9 +1,21 @@
+load(
+    "@rules_erlang//:erlang_app_info.bzl",
+    "ErlangAppInfo",
+)
 load(
     "@rules_erlang//tools:erlang_toolchain.bzl",
     "erlang_dirs",
 )
+load(
+    "@rules_erlang//:util.bzl",
+    "path_join",
+)
+load(
+    "@rules_erlang//private:util.bzl",
+    "additional_file_dest_relative_path",
+)
 
-def _impl(ctx):
+def _erlang_ls_config(ctx):
     out = ctx.actions.declare_file(ctx.label.name)
 
     (erlang_home, _, _) = erlang_dirs(ctx)
@@ -34,8 +46,54 @@ plt_path: bazel-bin/deps/rabbit/.base_plt.plt
     ]
 
 erlang_ls_config = rule(
-    implementation = _impl,
+    implementation = _erlang_ls_config,
     toolchains = [
         "@rules_erlang//tools:toolchain_type",
     ],
 )
+
+def _erlang_app_files(ctx, app, directory):
+    app_info = app[ErlangAppInfo]
+    app_path = path_join(directory, app_info.app_name)
+    files = []
+    for hdr in app_info.srcs + app_info.beam:
+        rp = additional_file_dest_relative_path(app.label, hdr)
+        dest = ctx.actions.declare_file(path_join(app_path, rp))
+        ctx.actions.symlink(output = dest, target_file = hdr)
+        files.append(dest)
+    return files
+
+def _erlang_ls_tree(ctx):
+    apps = ctx.attr.apps
+    deps = []
+
+    for app in apps:
+        app_info = app[ErlangAppInfo]
+        for dep in app_info.deps:
+            # this puts non rabbitmq plugins, like amqp10_client into deps,
+            # but maybe those should be in apps? Does it matter?
+            if dep not in deps and dep not in apps:
+                deps.append(dep)
+
+    files = []
+    for app in apps:
+        files.extend(
+            _erlang_app_files(ctx, app, path_join(ctx.label.name, "apps")),
+        )
+    for dep in deps:
+        files.extend(
+            _erlang_app_files(ctx, dep, path_join(ctx.label.name, "deps")),
+        )
+
+    return [
+        DefaultInfo(files = depset(files)),
+    ]
+
+erlang_ls_tree = rule(
+    implementation = _erlang_ls_tree,
+    attrs = {
+        "apps": attr.label_list(
+            providers = [ErlangAppInfo],
+        ),
+    },
+)