Add rust-objcopy as optional rust_toolchain attribute

Adds `rust-objcopy` as a separate filegroup and optional attribute on
`rust_toolchain`, following the same pattern as `rust-lld`.

The filegroup uses `allow_empty = True` for compatibility with Rust
versions before 1.84.0 where the binary is not available.

Author: avrabe

rust/private/repository_utils.bzl

@@ -90,12 +90,24 @@ filegroup(
 )
 """
 
-def BUILD_for_compiler(target_triple, include_linker = False):
+_build_file_for_objcopy_template = """\
+filegroup(
+    name = "rust-objcopy",
+    srcs = glob(
+        ["lib/rustlib/{target_triple}/bin/rust-objcopy{binary_ext}"],
+        allow_empty = True,
+    ),
+    visibility = ["//visibility:public"],
+)
+"""
+
+def BUILD_for_compiler(target_triple, include_linker = False, include_objcopy = False):
     """Emits a BUILD file the compiler archive.
 
     Args:
         target_triple (str): The triple of the target platform
         include_linker (bool): Whether to generate targets for linkers.
+        include_objcopy (bool): Whether to generate targets for rust-objcopy.
 
     Returns:
         str: The contents of a BUILD file
@@ -117,6 +129,14 @@ def BUILD_for_compiler(target_triple, include_linker = False):
             ),
         )
 
+    if include_objcopy:
+        content.append(
+            _build_file_for_objcopy_template.format(
+                binary_ext = system_to_binary_ext(target_triple.system),
+                target_triple = target_triple.str,
+            ),
+        )
+
     return "\n".join(content)
 
 _build_file_for_cargo_template = """\
@@ -324,6 +344,7 @@ rust_toolchain(
     rustc = "//:rustc",
     linker = {linker_label},
     linker_type = {linker_type},
+    rust_objcopy = {rust_objcopy_label},
     rustfmt = {rustfmt_label},
     cargo = "//:cargo",
     clippy_driver = "//:clippy_driver_bin",
@@ -361,6 +382,7 @@ def BUILD_for_rust_toolchain(
         include_rustfmt,
         include_llvm_tools,
         include_linker,
+        include_objcopy = False,
         stdlib_linkflags = None,
         extra_rustc_flags = None,
         extra_exec_rustc_flags = None,
@@ -381,6 +403,7 @@ def BUILD_for_rust_toolchain(
         include_rustfmt (bool): Whether rustfmt is present in the toolchain.
         include_llvm_tools (bool): Whether llvm-tools are present in the toolchain.
         include_linker (bool): Whether a linker is available in the toolchain.
+        include_objcopy (bool): Whether rust-objcopy is available in the toolchain.
         stdlib_linkflags (list, optional): Overridden flags needed for linking to rust
                                            stdlib, akin to BAZEL_LINKLIBS. Defaults to
                                            None.
@@ -418,6 +441,10 @@ def BUILD_for_rust_toolchain(
         linker_label = "//:rust-lld"
         linker_type = "direct"
 
+    rust_objcopy_label = None
+    if include_objcopy:
+        rust_objcopy_label = "//:rust-objcopy"
+
     return _build_file_for_rust_toolchain_template.format(
         toolchain_name = name,
         binary_ext = system_to_binary_ext(target_triple.system),
@@ -435,6 +462,7 @@ def BUILD_for_rust_toolchain(
         llvm_lib_label = repr(llvm_lib_label),
         linker_label = repr(linker_label),
         linker_type = repr(linker_type),
+        rust_objcopy_label = repr(rust_objcopy_label),
         extra_rustc_flags = extra_rustc_flags,
         extra_exec_rustc_flags = extra_exec_rustc_flags,
         opt_level = opt_level,
@@ -519,7 +547,7 @@ def load_rustfmt(ctx, target_triple, version, iso_date):
 
     return BUILD_for_rustfmt(target_triple), sha256
 
-def load_rust_compiler(ctx, iso_date, target_triple, version, include_linker = False):
+def load_rust_compiler(ctx, iso_date, target_triple, version, include_linker = False, include_objcopy = False):
     """Loads a rust compiler and yields corresponding BUILD for it
 
     Args:
@@ -528,6 +556,7 @@ def load_rust_compiler(ctx, iso_date, target_triple, version, include_linker = F
         target_triple (struct): The Rust-style target that this compiler runs on.
         version (str): The version of the tool among \"nightly\", \"beta\", or an exact version.
         include_linker (bool): Whether to include linker targets in the output BUILD contents.
+        include_objcopy (bool): Whether to include rust-objcopy targets in the output BUILD contents.
 
     Returns:
         Tuple[str, Dict[str, str]]: The BUILD file contents for this compiler and compiler library
@@ -543,7 +572,7 @@ def load_rust_compiler(ctx, iso_date, target_triple, version, include_linker = F
         version = version,
     )
 
-    return BUILD_for_compiler(target_triple, include_linker), sha256
+    return BUILD_for_compiler(target_triple, include_linker, include_objcopy), sha256
 
 def load_clippy(ctx, iso_date, target_triple, version):
     """Loads Clippy and yields corresponding BUILD for it

rust/repositories.bzl

@@ -449,13 +449,15 @@ def _rust_toolchain_tools_repository_impl(ctx):
     exec_triple = triple(ctx.attr.exec_triple)
 
     include_linker = True
+    include_objcopy = True
 
     rustc_content, rustc_sha256 = load_rust_compiler(
         ctx = ctx,
         iso_date = iso_date,
         target_triple = exec_triple,
         version = version,
         include_linker = include_linker,
+        include_objcopy = include_objcopy,
     )
     clippy_content, clippy_sha256 = load_clippy(
         ctx = ctx,
@@ -534,6 +536,7 @@ def _rust_toolchain_tools_repository_impl(ctx):
         include_rustfmt = not (not ctx.attr.rustfmt_version),
         include_llvm_tools = include_llvm_tools,
         include_linker = include_linker,
+        include_objcopy = include_objcopy,
         extra_rustc_flags = ctx.attr.extra_rustc_flags,
         extra_exec_rustc_flags = ctx.attr.extra_exec_rustc_flags,
         opt_level = ctx.attr.opt_level if ctx.attr.opt_level else None,
@@ -769,6 +772,7 @@ _RUST_ANALYZER_TOOLCHAIN_TOOLS_REPOSITORY_ATTRS = {
 def _rust_analyzer_toolchain_tools_repository_impl(repository_ctx):
     sha256s = dict(repository_ctx.attr.sha256s)
     include_linker = True
+    include_objcopy = True
 
     iso_date = None
     version = repository_ctx.attr.version
@@ -794,6 +798,7 @@ def _rust_analyzer_toolchain_tools_repository_impl(repository_ctx):
         target_triple = host_triple,
         version = version,
         include_linker = include_linker,
+        include_objcopy = include_objcopy,
     )
     build_contents = [rustc_content]
     sha256s.update(rustc_sha256)
@@ -929,6 +934,7 @@ def _rustfmt_toolchain_tools_repository_impl(repository_ctx):
     ))
 
     include_linker = True
+    include_objcopy = True
 
     iso_date = None
     version = repository_ctx.attr.version
@@ -949,6 +955,7 @@ def _rustfmt_toolchain_tools_repository_impl(repository_ctx):
         target_triple = exec_triple,
         version = version,
         include_linker = include_linker,
+        include_objcopy = include_objcopy,
     )
     rustfmt_content, rustfmt_sha256 = load_rustfmt(
         ctx = repository_ctx,

rust/toolchain.bzl

@@ -585,6 +585,7 @@ def _rust_toolchain_impl(ctx):
         llvm_cov = ctx.file.llvm_cov,
         llvm_profdata = ctx.file.llvm_profdata,
         llvm_lib = ctx.files.llvm_lib,
+        rust_objcopy = ctx.file.rust_objcopy,
         lto = lto,
         make_variables = make_variable_info,
         rust_doc = sysroot.rustdoc,
@@ -751,6 +752,11 @@ rust_toolchain = rule(
             doc = "LLVM tools that are shipped with the Rust toolchain.",
             allow_files = True,
         ),
+        "rust_objcopy": attr.label(
+            doc = "The location of the `rust-objcopy` binary. Can be a direct source or a filegroup containing one item.",
+            allow_single_file = True,
+            cfg = "exec",
+        ),
         "lto": attr.label(
             providers = [RustLtoInfo],
             default = Label("//rust/settings:lto"),