refactor(bazel): use configured Rust toolchain root

MODULE.bazel.lock

@@ -93,7 +93,7 @@
   "moduleExtensions": {
     "//bazel:rust.bzl%rust": {
       "general": {
-        "bzlTransitiveDigest": "0r4u+74QPphTHEzrdQIFSn4SfNM4AAJNlPyNGE8JwRs=",
+        "bzlTransitiveDigest": "4aaA6vAtrGES73j6RWZFmf/31/0PAazCSNi2ccK0w0E=",
         "usagesDigest": "jJoM2Hp1NbshT//puE4xIUfXdA0K6BRx1WTlsZIKFm4=",
         "recordedFileInputs": {},
         "recordedDirentsInputs": {},

bazel/BUILD

@@ -1,4 +1,5 @@
 exports_files([
+    "rust.BUILD.tpl",
     "rust.bzl",
     "utils.bzl",
 ])

bazel/rust.BUILD.tpl

@@ -0,0 +1,117 @@
+filegroup(
+    name = "rustc",
+    srcs = ["toolchain/bin/rustc"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "rustdoc",
+    srcs = ["toolchain/bin/rustdoc"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "cargo",
+    srcs = ["toolchain/bin/cargo"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "cargo_clippy",
+    srcs = ["toolchain/bin/cargo-clippy"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "clippy_driver",
+    srcs = ["toolchain/bin/clippy-driver"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "rustfmt",
+    srcs = ["toolchain/bin/rustfmt"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "cc",
+    srcs = ["toolchain/bin/cc"],
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "rustc_lib",
+    srcs = glob(
+        [
+            "rust/lib/*.so*",
+            "rust/lib/rustlib/{host_triple}/codegen-backends/*.so",
+            "rust/lib/rustlib/{host_triple}/lib/*.so*",
+            "rust/lib/rustlib/{host_triple}/lib/*.rmeta",
+        ],
+        allow_empty = True,
+    ),
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "rust_objcopy",
+    srcs = glob(
+        ["rust/lib/rustlib/{host_triple}/bin/rust-objcopy"],
+        allow_empty = True,
+    ),
+    visibility = ["//visibility:public"],
+)
+
+load("@rules_rust//rust:toolchain.bzl", "rust_stdlib_filegroup")
+
+rust_stdlib_filegroup(
+    name = "rust_std",
+    srcs = glob(
+        [
+            "rust/lib/rustlib/{host_triple}/lib/*.rlib",
+            "rust/lib/rustlib/{host_triple}/lib/*.rmeta",
+            "rust/lib/rustlib/{host_triple}/lib/*.so*",
+            "rust/lib/rustlib/{host_triple}/lib/*.a",
+            "rust/lib/rustlib/{host_triple}/lib/self-contained/**",
+        ],
+        allow_empty = True,
+    ),
+    visibility = ["//visibility:public"],
+)
+
+load("@rules_rust//rust:toolchain.bzl", "rust_toolchain")
+
+rust_toolchain(
+    name = "toolchain_impl",
+    rust_doc = ":rustdoc",
+    rust_std = ":rust_std",
+    rustc = ":rustc",
+    linker = ":cc",
+    linker_type = "indirect",
+    rust_objcopy = ":rust_objcopy",
+    rustfmt = ":rustfmt",
+    cargo = ":cargo",
+    clippy_driver = ":clippy_driver",
+    cargo_clippy = ":cargo_clippy",
+    rustc_lib = ":rustc_lib",
+    allocator_library = None,
+    global_allocator_library = None,
+    binary_ext = "",
+    staticlib_ext = ".a",
+    dylib_ext = ".so",
+    stdlib_linkflags = ["-ldl", "-lpthread"],
+    default_edition = "2024",
+    exec_triple = "{host_triple}",
+    target_triple = "{host_triple}",
+    version = "{release}",
+    channel = "stable",
+    visibility = ["//visibility:public"],
+)
+
+toolchain(
+    name = "rust",
+    toolchain = ":toolchain_impl",
+    toolchain_type = "@rules_rust//rust:toolchain_type",
+    visibility = ["//visibility:public"],
+)

bazel/rust.bzl

@@ -1,14 +1,9 @@
-load("//bazel:utils.bzl", "execute", "require")
+load("//bazel:utils.bzl", "execute", "require_env")
 
 
 def _rust_repository_impl(repository_ctx):
-    rustc = require(repository_ctx, "rustc")
+    root = repository_ctx.path(require_env(repository_ctx, "RUST_TOOLCHAIN_ROOT"))
-    rustdoc = require(repository_ctx, "rustdoc")
+    rustc = root.get_child("bin/rustc")
-    cargo = require(repository_ctx, "cargo")
-    cargo_clippy = require(repository_ctx, "cargo-clippy")
-    clippy_driver = require(repository_ctx, "clippy-driver")
-    rustfmt = require(repository_ctx, "rustfmt")
-    cc = require(repository_ctx, "cc")
 
     sysroot = execute(repository_ctx, [str(rustc), "--print", "sysroot"])
     verbose_version = execute(repository_ctx, [str(rustc), "-vV"])
@@ -26,148 +21,24 @@ def _rust_repository_impl(repository_ctx):
     if release == None:
         fail("rustc -vV did not report a release")
 
-    repository_ctx.symlink(rustc, "bin/rustc")
+    repository_ctx.symlink(root, "toolchain")
-    repository_ctx.symlink(rustdoc, "bin/rustdoc")
-    repository_ctx.symlink(cargo, "bin/cargo")
-    repository_ctx.symlink(cargo_clippy, "bin/cargo-clippy")
-    repository_ctx.symlink(clippy_driver, "bin/clippy-driver")
-    repository_ctx.symlink(rustfmt, "bin/rustfmt")
-    repository_ctx.symlink(cc, "bin/cc")
     repository_ctx.symlink(sysroot, "rust")
 
     repository_ctx.file("WORKSPACE.bazel", "")
-    repository_ctx.file("BUILD.bazel", _build_file(host_triple, release))
+    repository_ctx.template(
-
+        "BUILD.bazel",
-
+        Label("//bazel:rust.BUILD.tpl"),
-def _build_file(host_triple, release):
+        {
-    return """
+            "{host_triple}": host_triple,
-filegroup(
+            "{release}": release,
-    name = "rustc",
+        },
-    srcs = ["bin/rustc"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "rustdoc",
-    srcs = ["bin/rustdoc"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "cargo",
-    srcs = ["bin/cargo"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "cargo_clippy",
-    srcs = ["bin/cargo-clippy"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "clippy_driver",
-    srcs = ["bin/clippy-driver"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "rustfmt",
-    srcs = ["bin/rustfmt"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "cc",
-    srcs = ["bin/cc"],
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "rustc_lib",
-    srcs = glob(
-        [
-            "rust/lib/*.so*",
-            "rust/lib/rustlib/{host_triple}/codegen-backends/*.so",
-            "rust/lib/rustlib/{host_triple}/lib/*.so*",
-            "rust/lib/rustlib/{host_triple}/lib/*.rmeta",
-        ],
-        allow_empty = True,
-    ),
-    visibility = ["//visibility:public"],
-)
-
-filegroup(
-    name = "rust_objcopy",
-    srcs = glob(
-        ["rust/lib/rustlib/{host_triple}/bin/rust-objcopy"],
-        allow_empty = True,
-    ),
-    visibility = ["//visibility:public"],
-)
-
-load("@rules_rust//rust:toolchain.bzl", "rust_stdlib_filegroup")
-
-rust_stdlib_filegroup(
-    name = "rust_std",
-    srcs = glob(
-        [
-            "rust/lib/rustlib/{host_triple}/lib/*.rlib",
-            "rust/lib/rustlib/{host_triple}/lib/*.rmeta",
-            "rust/lib/rustlib/{host_triple}/lib/*.so*",
-            "rust/lib/rustlib/{host_triple}/lib/*.a",
-            "rust/lib/rustlib/{host_triple}/lib/self-contained/**",
-        ],
-        allow_empty = True,
-    ),
-    visibility = ["//visibility:public"],
-)
-
-load("@rules_rust//rust:toolchain.bzl", "rust_toolchain")
-
-rust_toolchain(
-    name = "toolchain_impl",
-    rust_doc = ":rustdoc",
-    rust_std = ":rust_std",
-    rustc = ":rustc",
-    linker = ":cc",
-    linker_type = "indirect",
-    rust_objcopy = ":rust_objcopy",
-    rustfmt = ":rustfmt",
-    cargo = ":cargo",
-    clippy_driver = ":clippy_driver",
-    cargo_clippy = ":cargo_clippy",
-    rustc_lib = ":rustc_lib",
-    allocator_library = None,
-    global_allocator_library = None,
-    binary_ext = "",
-    staticlib_ext = ".a",
-    dylib_ext = ".so",
-    stdlib_linkflags = ["-ldl", "-lpthread"],
-    default_edition = "2024",
-    exec_triple = "{host_triple}",
-    target_triple = "{host_triple}",
-    version = "{release}",
-    channel = "stable",
-    visibility = ["//visibility:public"],
-)
-
-toolchain(
-    name = "rust",
-    toolchain = ":toolchain_impl",
-    toolchain_type = "@rules_rust//rust:toolchain_type",
-    visibility = ["//visibility:public"],
-)
-""".format(
-        host_triple = host_triple,
-        release = release,
     )
 
 
 rust_repository = repository_rule(
     implementation = _rust_repository_impl,
     local = True,
-    environ = ["PATH"],
+    environ = ["RUST_TOOLCHAIN_ROOT"],
 )
 
 

bazel/utils.bzl

@@ -1,8 +1,8 @@
-def require(repository_ctx, executable):
+def require_env(repository_ctx, variable):
-    path = repository_ctx.which(executable)
+    value = repository_ctx.os.environ.get(variable)
-    if path == None:
+    if not value:
-        fail("{} must be available in PATH.".format(executable))
+        fail("{} must be set.".format(variable))
-    return path
+    return value
 
 
 def execute(repository_ctx, arguments):

configs/nixos/modules/shell/rust.nix

@@ -8,18 +8,28 @@
 let
   cfg = config.modules.shell.rust;
   user = config.user.name;
+  toolchain = pkgs.symlinkJoin {
+    name = "rust-toolchain";
+    paths = with pkgs; [
+      cargo
+      clippy
+      gcc
+      rustc
+      rustfmt
+    ];
+  };
 in
 {
   options.modules.shell.rust.enable = lib.mkEnableOption "Rust tools for the primary user's shell environment";
 
   config = lib.mkIf cfg.enable {
-    home-manager.users.${user}.home.packages = with pkgs; [
+    home-manager.users.${user} = {
-      cargo
+      home.packages = [
-      clippy
+        toolchain
-      gcc
+        pkgs.rust-analyzer
-      rust-analyzer
+      ];
-      rustc
+
-      rustfmt
+      home.sessionVariables.RUST_TOOLCHAIN_ROOT = "${toolchain}";
-    ];
+    };
   };
 }