Add missing rustc binaries to rustc_lib filegroup (bazelbuild#3727)

## Summary

Add `rust-objcopy` and `wasm-component-ld` to the `rustc_lib` filegroup
in `repository_utils.bzl`. These binaries are present in recent rustc
distributions (wasm-component-ld since 1.82.0, rust-objcopy since
1.84.0) but were not previously declared.

### Changes

- **Binary Declaration**: Add `rust-objcopy{binary_ext}` and
`wasm-component-ld{binary_ext}` to the rustc_lib filegroup glob patterns

### Context

On Windows, Bazel copies files into the sandbox rather than symlinking,
so only explicitly listed files are available. This caused wasm32-wasip2
builds to fail with `linker 'wasm-component-ld.exe' not found`.

On Linux/macOS, the issue was masked by symlink-based sandboxing which
allowed rustc to access unlisted files in the same directory.

---------

Co-authored-by: UebelAndre <github@uebelandre.com>

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 = """\
@@ -325,6 +345,7 @@ 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",
@@ -362,6 +383,7 @@ 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,
@@ -382,6 +404,7 @@ 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.
@@ -419,6 +442,10 @@ 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),
@@ -436,6 +463,7 @@ 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,
@@ -520,7 +548,7 @@ 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:
@@ -529,6 +557,7 @@ 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
@@ -544,7 +573,7 @@ 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

@@ -434,6 +434,19 @@ def _include_llvm_tools(version, iso_date):
 
     return False
 
+def _include_rust_objcopy(version, iso_date):
+    """rust-objcopy is available in Rust 1.84.0+ and nightly builds after 2024-10-17"""
+    if version in ("nightly", "beta"):
+        if iso_date > "2024-10-17":
+            return True
+        return False
+
+    version_semver = semver(version)
+    if version_semver.major >= 1 and version_semver.minor >= 84:
+        return True
+
+    return False
+
 def _rust_toolchain_tools_repository_impl(ctx):
     """The implementation of the rust toolchain tools repository rule."""
     sha256s = dict(ctx.attr.sha256s)
@@ -450,12 +463,16 @@ def _rust_toolchain_tools_repository_impl(ctx):
 
     include_linker = True
 
+    # rust-objcopy is only available in Rust 1.84.0+
+    include_objcopy = _include_rust_objcopy(version, iso_date)
+
     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 +551,7 @@ 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,

rust/toolchain.bzl

@@ -152,7 +152,7 @@ def _symlink_sysroot_tree(ctx, name, target, target_files = None):
     tree_files = []
     if target_files == None:
         target_files = target.files
-    for file in target.files.to_list():
+    for file in target_files.to_list():
         # Parse the path to the file relative to the workspace root so a
         # symlink matching this path can be created within the sysroot.
 
@@ -284,11 +284,14 @@ def _generate_sysroot(
                 linker.label,
             ))
         linker_bin = linker_files[0]
+
+        # Extract lib/rustlib/{triple}/bin from linker source path.
+        # rustc adds {sysroot}/lib/rustlib/{host}/bin/ to PATH when invoking
+        # linkers, so tools like wasm-component-ld can find rust-lld there.
         dest = "bin"
-        if "/bin/" in linker_bin.path:
-            _, _, subdir = linker_bin.path.partition("/bin/")
-            if subdir:
-                dest = "bin/{}".format(subdir[:-len("/" + linker_bin.basename)]).rstrip("/")
+        if "/lib/rustlib/" in linker_bin.dirname:
+            idx = linker_bin.dirname.find("/lib/rustlib/")
+            dest = linker_bin.dirname[idx + 1:]
 
         sysroot_linker = _symlink_sysroot_bin(ctx, name, dest, linker_bin)
         sysroot_linker_files = _symlink_sysroot_tree(ctx, name, linker, linker[DefaultInfo].default_runfiles.files)
@@ -585,6 +588,7 @@ 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,
@@ -780,6 +784,11 @@ rust_toolchain = rule(
             cfg = "exec",
             mandatory = 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",
+        ),
         "rust_std": attr.label(
             doc = "The Rust standard library.",
             mandatory = True,