Do not attempt to instrument rust code for coverage if rust_toolchain.llvm-cov is None

docs/flatten.md

@@ -1123,8 +1123,8 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
 | <a id="rust_toolchain-dylib_ext"></a>dylib_ext |  The extension for dynamic libraries created from rustc.   | String | required |  |
 | <a id="rust_toolchain-env"></a>env |  Environment variables to set in actions.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_toolchain-exec_triple"></a>exec_triple |  The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations   | String | required |  |
-| <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
-| <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
+| <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item. If None, rust code is not instrumented for coverage.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
+| <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item. If <code>llvm_cov</code> is None, this can be None as well and rust code is not instrumented for coverage.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-opt_level"></a>opt_level |  Rustc optimization levels.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {"dbg": "0", "fastbuild": "0", "opt": "3"} |
 | <a id="rust_toolchain-os"></a>os |  The operating system for the current toolchain   | String | required |  |

docs/rust_repositories.md

@@ -96,8 +96,8 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
 | <a id="rust_toolchain-dylib_ext"></a>dylib_ext |  The extension for dynamic libraries created from rustc.   | String | required |  |
 | <a id="rust_toolchain-env"></a>env |  Environment variables to set in actions.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_toolchain-exec_triple"></a>exec_triple |  The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations   | String | required |  |
-| <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
-| <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
+| <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item. If None, rust code is not instrumented for coverage.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
+| <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item. If <code>llvm_cov</code> is None, this can be None as well and rust code is not instrumented for coverage.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-opt_level"></a>opt_level |  Rustc optimization levels.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {"dbg": "0", "fastbuild": "0", "opt": "3"} |
 | <a id="rust_toolchain-os"></a>os |  The operating system for the current toolchain   | String | required |  |

rust/private/rust.bzl

@@ -466,7 +466,10 @@ def _rust_test_common(ctx, toolchain, output):
         getattr(ctx.attr, "env", {}),
         data,
     )
-    if ctx.configuration.coverage_enabled:
+    if toolchain.llvm_cov and ctx.configuration.coverage_enabled:
+        if not toolchain.llvm_profdata:
+            fail("toolchain.llvm_profdata is required if toolchain.llvm_cov is set.")
+
         env["RUST_LLVM_COV"] = toolchain.llvm_cov.path
         env["RUST_LLVM_PROFDATA"] = toolchain.llvm_profdata.path
     providers.append(testing.TestEnvironment(env))

rust/private/rustc.bzl

@@ -805,7 +805,7 @@ def construct_arguments(
         rustc_flags.add("--extern")
         rustc_flags.add("proc_macro")
 
-    if ctx.configuration.coverage_enabled:
+    if toolchain.llvm_cov and ctx.configuration.coverage_enabled:
         rustc_flags.add("--codegen=instrument-coverage")
 
     # Make bin crate data deps available to tests.

rust/toolchain.bzl

@@ -577,12 +577,12 @@ rust_toolchain = rule(
             mandatory = True,
         ),
         "llvm_cov": attr.label(
-            doc = "The location of the `llvm-cov` binary. Can be a direct source or a filegroup containing one item.",
+            doc = "The location of the `llvm-cov` binary. Can be a direct source or a filegroup containing one item. If None, rust code is not instrumented for coverage.",
             allow_single_file = True,
             cfg = "exec",
         ),
         "llvm_profdata": attr.label(
-            doc = "The location of the `llvm-profdata` binary. Can be a direct source or a filegroup containing one item.",
+            doc = "The location of the `llvm-profdata` binary. Can be a direct source or a filegroup containing one item. If `llvm_cov` is None, this can be None as well and rust code is not instrumented for coverage.",
             allow_single_file = True,
             cfg = "exec",
         ),