[toolchains] Add opt-in nightly rustc-dev toolchains

README.md

@@ -132,6 +132,36 @@ https://bazelbuild.github.io/rules_rust/rust_analyzer.html#vscode
 
 ## Advanced Options
 
+<details>
+<summary>Enable nightly rustc-dev components</summary>
+
+Nightly crates that depend on `rustc_private` need the `rustc-dev` component in the
+compiler sysroot. Opt into that only for the nightly toolchain that needs it:
+
+```bzl
+toolchains.toolchain(
+    name = "nightly_rust_toolchains",
+    edition = "2024",
+    include_rustc_dev = True,
+    version = "nightly/2026-03-05",
+)
+use_repo(toolchains, "nightly_rust_toolchains")
+register_toolchains("@nightly_rust_toolchains//:all")
+```
+
+`include_rustc_dev` is accepted only for nightly Rust versions. It keeps the default
+toolchain path unchanged and exposes separate `*_with_dev` toolchains when a build sets
+both:
+
+```bash
+bazel build \
+  --@rules_rust//rust/toolchain/channel=nightly \
+  --@rules_rs//rs/toolchains/rustc_dev:enabled \
+  //...
+```
+
+</details>
+
 <details>
 <summary>Use legacy rules_rust toolchains or platforms</summary>
 

rs/private/BUILD.bazel

@@ -184,6 +184,27 @@ bzl_library(
     ],
 )
 
+bzl_library(
+    name = "rustc_dev_repository",
+    srcs = ["rustc_dev_repository.bzl"],
+    visibility = ["//rs:__subpackages__"],
+    deps = [
+        "//rs/private:rust_repository_utils",
+        "@rules_rust//rust/platform:bzl_lib",
+    ],
+)
+
+bzl_library(
+    name = "rustc_with_dev_repository",
+    srcs = ["rustc_with_dev_repository.bzl"],
+    visibility = ["//rs:__subpackages__"],
+    deps = [
+        "@bazel_features//:features",
+        "@rules_rust//rust/platform:bzl_lib",
+        "@rules_rust//rust/private:bzl_lib",
+    ],
+)
+
 bzl_library(
     name = "stdlib_repository",
     srcs = ["stdlib_repository.bzl"],

rs/private/rustc_dev_repository.bzl

@@ -0,0 +1,27 @@
+load("@rules_rust//rust/platform:triple.bzl", "triple")
+load(":rust_repository_utils.bzl", "RUST_REPOSITORY_COMMON_ATTR", "download_and_extract")
+
+def _rustc_dev_repository_impl(rctx):
+    exec_triple = triple(rctx.attr.triple)
+    download_and_extract(rctx, "rustc-dev", "rustc-dev", exec_triple)
+
+    rctx.file(
+        "BUILD.bazel",
+        """\
+filegroup(
+    name = "rustc_dev_libs",
+    srcs = glob(
+        ["lib/rustlib/{triple}/lib/*.rlib"],
+        allow_empty = True,
+    ),
+    visibility = ["//visibility:public"],
+)
+""".format(triple = exec_triple.str),
+    )
+
+    return rctx.repo_metadata(reproducible = True)
+
+rustc_dev_repository = repository_rule(
+    implementation = _rustc_dev_repository_impl,
+    attrs = RUST_REPOSITORY_COMMON_ATTR,
+)

rs/private/rustc_with_dev_repository.bzl

@@ -0,0 +1,79 @@
+load("@bazel_features//:features.bzl", "bazel_features")
+load("@rules_rust//rust/platform:triple.bzl", "triple")
+load(
+    "@rules_rust//rust/private:repository_utils.bzl",
+    "BUILD_for_compiler",
+)
+
+def _symlink_children(rctx, source_dir, destination_dir):
+    if not source_dir.exists or not source_dir.is_dir:
+        return
+
+    rctx.file("{}/.generated".format(destination_dir), "")
+    for entry in source_dir.readdir():
+        if entry.is_dir or entry.basename.startswith("."):
+            continue
+
+        destination = "{}/{}".format(destination_dir, entry.basename)
+        if not rctx.path(destination).exists:
+            rctx.symlink(entry, destination)
+
+def _rustc_with_dev_repository_impl(rctx):
+    exec_triple = triple(rctx.attr.triple)
+    rustc_repo_root = rctx.path(rctx.attr.rustc_repo_build_file).dirname
+    rustc_dev_repo_root = rctx.path(rctx.attr.rustc_dev_repo_build_file).dirname
+
+    # Keep the ordinary rustc repository lean. This merged sysroot is materialized
+    # only when a dev-enabled toolchain is actually selected.
+    rctx.symlink(rustc_repo_root.get_child("bin"), "bin")
+
+    rustc_lib_root = rustc_repo_root.get_child("lib")
+    rustc_rustlib_root = rustc_lib_root.get_child("rustlib").get_child(exec_triple.str)
+    rustc_dev_lib_root = rustc_dev_repo_root.get_child("lib").get_child("rustlib").get_child(exec_triple.str)
+
+    _symlink_children(rctx, rustc_lib_root, "lib")
+    rctx.symlink(
+        rustc_rustlib_root.get_child("bin"),
+        "lib/rustlib/{}/bin".format(exec_triple.str),
+    )
+    _symlink_children(
+        rctx,
+        rustc_rustlib_root.get_child("codegen-backends"),
+        "lib/rustlib/{}/codegen-backends".format(exec_triple.str),
+    )
+    _symlink_children(
+        rctx,
+        rustc_rustlib_root.get_child("lib"),
+        "lib/rustlib/{}/lib".format(exec_triple.str),
+    )
+    _symlink_children(
+        rctx,
+        rustc_dev_lib_root.get_child("lib"),
+        "lib/rustlib/{}/lib".format(exec_triple.str),
+    )
+
+    # `rustc_private` crates link against compiler `.rlib`s from rustc-dev.
+    # The upstream compiler BUILD omits `.rlib`s because ordinary toolchains do
+    # not need them, so extend the merged sysroot manifest only for this variant.
+    build_file = BUILD_for_compiler(exec_triple, include_objcopy = True)
+    build_file = build_file.replace(
+        '"lib/rustlib/{}/lib/*.rmeta",'.format(exec_triple.str),
+        '\n'.join([
+            '"lib/rustlib/{}/lib/*.rmeta",'.format(exec_triple.str),
+            '            "lib/rustlib/{}/lib/*.rlib",'.format(exec_triple.str),
+        ]),
+    )
+    rctx.file("BUILD.bazel", build_file)
+
+    return rctx.repo_metadata(
+        reproducible = bazel_features.external_deps.repo_rules_relativize_symlinks,
+    )
+
+rustc_with_dev_repository = repository_rule(
+    implementation = _rustc_with_dev_repository_impl,
+    attrs = {
+        "rustc_repo_build_file": attr.label(allow_single_file = True, mandatory = True),
+        "rustc_dev_repo_build_file": attr.label(allow_single_file = True, mandatory = True),
+        "triple": attr.string(mandatory = True),
+    },
+)

rs/private/toolchains_repository.bzl

@@ -9,6 +9,7 @@ load("@rules_rs//rs/toolchains:declare_rustfmt_toolchains.bzl", "declare_rustfmt
 declare_rustc_toolchains(
     version = {version},
     edition = {edition},
+    include_rustc_dev = {include_rustc_dev},
     extra_rustc_flags = {extra_rustc_flags},
     extra_exec_rustc_flags = {extra_exec_rustc_flags},
 )
@@ -28,6 +29,7 @@ declare_rust_analyzer_toolchains(
             rustfmt_version = repr(rctx.attr.rustfmt_version),
             rust_analyzer_version = repr(rctx.attr.rust_analyzer_version),
             edition = repr(rctx.attr.edition),
+            include_rustc_dev = repr(rctx.attr.include_rustc_dev),
             extra_rustc_flags = repr(rctx.attr.extra_rustc_flags),
             extra_exec_rustc_flags = repr(rctx.attr.extra_exec_rustc_flags),
         ),
@@ -42,6 +44,7 @@ toolchains_repository = repository_rule(
         "rustfmt_version": attr.string(mandatory = True),
         "rust_analyzer_version": attr.string(mandatory = True),
         "edition": attr.string(mandatory = True),
+        "include_rustc_dev": attr.bool(),
         "extra_rustc_flags": attr.string_list_dict(),
         "extra_exec_rustc_flags": attr.string_list_dict(),
     },

rs/toolchains/BUILD.bazel

@@ -48,7 +48,9 @@ bzl_library(
         "//rs/private:rust_analyzer_repository",
         "//rs/private:rust_repository_utils",
         "//rs/private:rust_src_repository",
+        "//rs/private:rustc_dev_repository",
         "//rs/private:rustc_repository",
+        "//rs/private:rustc_with_dev_repository",
         "//rs/private:rustfmt_repository",
         "//rs/private:stdlib_repository",
         "//rs/private:toolchains_repository",

rs/toolchains/declare_rustc_toolchains.bzl

@@ -20,6 +20,7 @@ def declare_rustc_toolchains(
         *,
         version,
         edition,
+        include_rustc_dev = False,
         extra_rustc_flags = {},
         extra_exec_rustc_flags = {},
         execs = SUPPORTED_EXEC_TRIPLES,
@@ -34,6 +35,7 @@ def declare_rustc_toolchains(
         triple_suffix = exec_triple.system + "_" + exec_triple.arch
 
         rustc_repo_label = "@rustc_{}_{}//:".format(triple_suffix, version_key)
+        rustc_with_dev_repo_label = "@rustc_with_dev_{}_{}//:".format(triple_suffix, version_key)
         cargo_repo_label = "@cargo_{}_{}//:".format(triple_suffix, version_key)
         clippy_repo_label = "@clippy_{}_{}//:".format(triple_suffix, version_key)
 
@@ -42,6 +44,7 @@ def declare_rustc_toolchains(
             exec_triple.arch,
             version_key,
         )
+        rust_toolchain_with_dev_name = rust_toolchain_name + "_with_dev"
 
         rust_std_select = {}
         target_triple_select = {}
@@ -134,8 +137,44 @@ def declare_rustc_toolchains(
             **rust_toolchain_kwargs
         )
 
+        if include_rustc_dev:
+            # Keep the ordinary toolchains registered for the default path, and
+            # expose parallel dev-enabled variants only to configurations that
+            # explicitly request the merged rustc-dev sysroot.
+            rust_toolchain_with_dev_kwargs = dict(rust_toolchain_kwargs)
+            rust_toolchain_with_dev_kwargs.update(
+                rust_doc = "{}rustdoc".format(rustc_with_dev_repo_label),
+                rustc = "{}rustc".format(rustc_with_dev_repo_label),
+                rust_objcopy = "{}rust-objcopy".format(rustc_with_dev_repo_label),
+                rustc_lib = "{}rustc_lib".format(rustc_with_dev_repo_label),
+            )
+
+            rust_toolchain(
+                name = rust_toolchain_with_dev_name,
+                process_wrapper = "@rules_rust//util/process_wrapper",
+                **rust_toolchain_with_dev_kwargs
+            )
+
+            rust_toolchain(
+                name = rust_toolchain_with_dev_name + "_bootstrap",
+                bootstrapping = True,
+                process_wrapper = "@rules_rust//util/process_wrapper:bootstrap_process_wrapper",
+                **rust_toolchain_with_dev_kwargs
+            )
+
         for target_triple in targets:
             target_key = sanitize_triple(target_triple)
+            bootstrapped_target_settings = [
+                "@rules_rust//rust/private:bootstrapped",
+                "@rules_rust//rust/toolchain/channel:" + channel,
+            ]
+            bootstrapping_target_settings = [
+                "@rules_rust//rust/private:bootstrapping",
+                "@rules_rust//rust/toolchain/channel:" + channel,
+            ]
+            if include_rustc_dev:
+                bootstrapped_target_settings.append("@rules_rs//rs/toolchains/rustc_dev:disabled")
+                bootstrapping_target_settings.append("@rules_rs//rs/toolchains/rustc_dev:disabled")
 
             native.toolchain(
                 name = "{}_{}_to_{}_{}".format(exec_triple.system, exec_triple.arch, target_key, version_key),
@@ -144,10 +183,7 @@ def declare_rustc_toolchains(
                     "@platforms//cpu:" + exec_triple.arch,
                 ],
                 target_compatible_with = triple_to_constraint_set(target_triple),
-                target_settings = [
-                    "@rules_rust//rust/private:bootstrapped",
-                    "@rules_rust//rust/toolchain/channel:" + channel,
-                ],
+                target_settings = bootstrapped_target_settings,
                 toolchain = rust_toolchain_name,
                 toolchain_type = "@rules_rust//rust:toolchain_type",
                 visibility = ["//visibility:public"],
@@ -160,11 +196,43 @@ def declare_rustc_toolchains(
                     "@platforms//cpu:" + exec_triple.arch,
                 ],
                 target_compatible_with = triple_to_constraint_set(target_triple),
-                target_settings = [
-                    "@rules_rust//rust/private:bootstrapping",
-                    "@rules_rust//rust/toolchain/channel:" + channel,
-                ],
+                target_settings = bootstrapping_target_settings,
                 toolchain = rust_toolchain_name + "_bootstrap",
                 toolchain_type = "@rules_rust//rust:toolchain_type",
                 visibility = ["//visibility:public"],
             )
+
+            if include_rustc_dev:
+                native.toolchain(
+                    name = "{}_{}_to_{}_{}_with_dev".format(exec_triple.system, exec_triple.arch, target_key, version_key),
+                    exec_compatible_with = [
+                        "@platforms//os:" + exec_triple.system,
+                        "@platforms//cpu:" + exec_triple.arch,
+                    ],
+                    target_compatible_with = triple_to_constraint_set(target_triple),
+                    target_settings = [
+                        "@rules_rust//rust/private:bootstrapped",
+                        "@rules_rust//rust/toolchain/channel:" + channel,
+                        "@rules_rs//rs/toolchains/rustc_dev:enabled_setting",
+                    ],
+                    toolchain = rust_toolchain_with_dev_name,
+                    toolchain_type = "@rules_rust//rust:toolchain_type",
+                    visibility = ["//visibility:public"],
+                )
+
+                native.toolchain(
+                    name = "{}_{}_to_{}_{}_bootstrap_with_dev".format(exec_triple.system, exec_triple.arch, target_key, version_key),
+                    exec_compatible_with = [
+                        "@platforms//os:" + exec_triple.system,
+                        "@platforms//cpu:" + exec_triple.arch,
+                    ],
+                    target_compatible_with = triple_to_constraint_set(target_triple),
+                    target_settings = [
+                        "@rules_rust//rust/private:bootstrapping",
+                        "@rules_rust//rust/toolchain/channel:" + channel,
+                        "@rules_rs//rs/toolchains/rustc_dev:enabled_setting",
+                    ],
+                    toolchain = rust_toolchain_with_dev_name + "_bootstrap",
+                    toolchain_type = "@rules_rust//rust:toolchain_type",
+                    visibility = ["//visibility:public"],
+                )