Update rust_stdlib_filegroup to detect profiler_builtins (bazelbuild#3958)

This change adds a `coverage_enabled` to `rust_toolchain` that should be
used to identify if the toolchain supports coverage. This would allow
repositories which use MUSL to run `bazel coverage //...` without
running into a linker error. The downside is that they will get no
coverage but this would already be the case due to the linker error.
More details on rust-lang/rust#79556

Author: UebelAndre

rust/private/providers.bzl

@@ -136,6 +136,7 @@ StdLibInfo = provider(
         "between_core_and_std_files": "List[File]: `.a` files related to all modules except `adler`, `alloc`, `compiler_builtins`, `core`, and `std`.",
         "core_files": "List[File]: `.a` files related to the `core` and `adler` modules",
         "dot_a_files": "Depset[File]: Generated `.a` files",
+        "has_profiler_builtins": "bool: Whether the sysroot contains the profiler_builtins rlib, required for -Cinstrument-coverage.",
         "memchr_files": "Depset[File]: `.a` files associated with the `memchr` module.",
         "panic_files": "Depset[File]: `.a` files associated with `panic_unwind` and `panic_abort`.",
         "self_contained_files": "List[File]: All `.o` files from the `self-contained` directory.",

rust/private/rust.bzl

@@ -506,7 +506,7 @@ def _rust_test_impl(ctx):
         data,
         {},
     )
-    if toolchain.llvm_cov and ctx.configuration.coverage_enabled:
+    if toolchain.coverage_supported and ctx.configuration.coverage_enabled:
         if not toolchain.llvm_profdata:
             fail("toolchain.llvm_profdata is required if toolchain.llvm_cov is set.")
 

rust/private/rustc.bzl

@@ -1200,7 +1200,7 @@ def construct_arguments(
         rustc_flags.add("--extern")
         rustc_flags.add("proc_macro")
 
-    if toolchain.llvm_cov and ctx.configuration.coverage_enabled:
+    if toolchain.coverage_supported and ctx.configuration.coverage_enabled:
         # https://doc.rust-lang.org/rustc/instrument-coverage.html
         rustc_flags.add("--codegen=instrument-coverage")
 
@@ -1687,7 +1687,7 @@ def rustc_compile_action(
         outputs = [crate_info.output]
 
     coverage_runfiles = []
-    if toolchain.llvm_cov and ctx.configuration.coverage_enabled and crate_info.is_test:
+    if toolchain.coverage_supported and ctx.configuration.coverage_enabled and crate_info.is_test:
         coverage_runfiles = [toolchain.llvm_cov, toolchain.llvm_profdata] + toolchain.llvm_lib
         collect_cc_coverage = getattr(ctx.executable, "_collect_cc_coverage", None)
         if not collect_cc_coverage:

rust/toolchain.bzl

@@ -56,6 +56,7 @@ def _rust_stdlib_filegroup_impl(ctx):
     panic_files = []
 
     std_rlibs = [f for f in rust_std if f.basename.endswith(".rlib")]
+    has_profiler_builtins = any(["profiler_builtins" in f.basename for f in std_rlibs])
     if std_rlibs:
         # test depends on std
         # std depends on everything except test
@@ -116,6 +117,7 @@ def _rust_stdlib_filegroup_impl(ctx):
             alloc_files = alloc_files,
             self_contained_files = self_contained_files,
             panic_files = panic_files,
+            has_profiler_builtins = has_profiler_builtins,
             srcs = ctx.attr.srcs,
         ),
     ]
@@ -587,6 +589,7 @@ def _rust_toolchain_impl(ctx):
         linker = sysroot.linker,
         linker_preference = linker_preference,
         linker_type = ctx.attr.linker_type or None,
+        coverage_supported = bool(ctx.file.llvm_cov) and ctx.attr.rust_std[rust_common.stdlib_info].has_profiler_builtins,
         llvm_cov = ctx.file.llvm_cov,
         llvm_profdata = ctx.file.llvm_profdata,
         llvm_lib = ctx.files.llvm_lib,