Include all toolchain files in the current toolchain (bazelbuild#2336)

rustc assumes it can read things like librustc_driver, and if you don't
include it, it gets sad.

rust/private/toolchain_utils.bzl

@@ -81,20 +81,11 @@ toolchain_files = rule(
 def _current_rust_toolchain_impl(ctx):
     toolchain = ctx.toolchains[str(Label("@rules_rust//rust:toolchain_type"))]
 
-    files = [
-        toolchain.rustc,
-        toolchain.rust_doc,
-        toolchain.cargo,
-    ]
-
-    if toolchain.rustfmt:
-        files.append(toolchain.rustfmt)
-
     return [
         toolchain,
         toolchain.make_variables,
         DefaultInfo(
-            files = depset(files),
+            files = toolchain.all_files,
         ),
     ]
 

test/toolchain/BUILD.bazel

@@ -1,3 +1,19 @@
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load(":toolchain_test.bzl", "toolchain_test_suite")
 
 toolchain_test_suite(name = "toolchain_test_suite")
+
+genrule(
+    name = "inspect",
+    outs = ["rustc-cfg"],
+    # rustc assumes it can read things like librustc_driver in order to run this command.
+    # This is a test to ensure we supply all of the files rustc needs as part of the current_rust_toolchain.
+    cmd = "$(RUSTC) --print=cfg > $@",
+    toolchains = ["@rules_rust//rust/toolchain:current_rust_toolchain"],
+    tools = ["@rules_rust//rust/toolchain:current_rust_toolchain"],
+)
+
+build_test(
+    name = "inspect_build_test",
+    targets = [":inspect"],
+)