Updated //tools/rustfmt to dynamically work within rules_rust its…

…elf (#883)

tools/rustfmt/BUILD.bazel

@@ -1,8 +1,12 @@
 load("//rust:defs.bzl", "rust_binary", "rust_clippy", "rust_library")
+load(":rustfmt_utils.bzl", "aspect_repository")
 
 package(default_visibility = ["//visibility:public"])
 
-exports_files(["rustfmt.toml"])
+exports_files([
+    "rustfmt.toml",
+    "rustfmt_utils.bzl",
+])
 
 rust_library(
     name = "rustfmt_lib",
@@ -30,6 +34,9 @@ rust_binary(
         "//:rustfmt.toml",
     ],
     edition = "2018",
+    rustc_env = {
+        "ASPECT_REPOSITORY": aspect_repository(),
+    },
     deps = [
         ":rustfmt_lib",
         "//util/label",

tools/rustfmt/rustfmt_utils.bzl

@@ -0,0 +1,18 @@
+"""A helper module for the `@rules_rust//tools/rustfmt` package"""
+
+def aspect_repository():
+    """Determines the repository name to use for the `rustfmt_manifest` aspect in `rustfmt` binaries.
+
+    The `//tools/rustfmt` target has a hard coded `--aspects` command built into it.
+    This function is designed to allow for this aspect to be updated to work within
+    the `rules_rust` repository itself since aspects do not work if the repository name
+    is explicitly set.
+
+    https://github.com/bazelbuild/rules_rust/issues/749
+
+    Returns:
+        str: The string to use for the `rustfmt_aspect` repository
+    """
+    if native.repository_name() == "@":
+        return ""
+    return native.repository_name()

tools/rustfmt/srcs/main.rs

@@ -75,9 +75,12 @@ fn query_rustfmt_targets(options: &Config) -> Vec<String> {
 /// arguments to use when formatting the sources of those targets.
 fn generate_rustfmt_target_manifests(options: &Config, targets: &[String]) {
     let build_args = vec![
-        "build",
-        "--aspects=@rules_rust//rust:defs.bzl%rustfmt_aspect",
-        "--output_groups=rustfmt_manifest",
+        "build".to_owned(),
+        format!(
+            "--aspects={}//rust:defs.bzl%rustfmt_aspect",
+            env!("ASPECT_REPOSITORY")
+        ),
+        "--output_groups=rustfmt_manifest".to_owned(),
     ];
 
     let child = Command::new(&options.bazel)