coverage: Correctly report and check LLVM's coverage mapping version

Author: Zalathar

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -18,11 +18,11 @@ use rustc_span::Symbol;
 
 /// Generates and exports the Coverage Map.
 ///
-/// Rust Coverage Map generation supports LLVM Coverage Mapping Format version
-/// 6 (zero-based encoded as 5), as defined at
-/// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
+/// Rust Coverage Map generation supports LLVM Coverage Mapping Format versions
+/// 6 and 7 (encoded as 5 and 6 respectively), as described at
+/// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/18.0-2024-02-13/llvm/docs/CoverageMappingFormat.rst).
 /// These versions are supported by the LLVM coverage tools (`llvm-profdata` and `llvm-cov`)
-/// bundled with Rust's fork of LLVM.
+/// distributed in the `llvm-tools-preview` rustup component.
 ///
 /// Consequently, Rust's bundled version of Clang also generates Coverage Maps compliant with
 /// the same version. Clang's implementation of Coverage Map generation was referenced when
@@ -32,10 +32,17 @@ use rustc_span::Symbol;
 pub fn finalize(cx: &CodegenCx<'_, '_>) {
     let tcx = cx.tcx;
 
-    // Ensure the installed version of LLVM supports Coverage Map Version 6
-    // (encoded as a zero-based value: 5), which was introduced with LLVM 13.
+    // Ensure that LLVM is using a version of the coverage mapping format that
+    // we know about. Supported versions (encoded as n-1) are:
+    // - `CovMapVersion::Version6` (5) used by LLVM 13-17
+    // - `CovMapVersion::Version7` (6) used by LLVM 18
     let version = coverageinfo::mapping_version();
-    assert_eq!(version, 5, "The `CoverageMappingVersion` exposed by `llvm-wrapper` is out of sync");
+    let expected_versions = 5..=6;
+    assert!(
+        expected_versions.contains(&version),
+        "Coverage mapping version exposed by `llvm-wrapper` is out of sync; \
+        expected {expected_versions:?} but was {version}"
+    );
 
     debug!("Generating coverage map for CodegenUnit: `{}`", cx.codegen_unit.name());
 

compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp

@@ -205,5 +205,7 @@ extern "C" void LLVMRustCoverageWriteMappingVarNameToString(RustStringRef Str) {
 }
 
 extern "C" uint32_t LLVMRustCoverageMappingVersion() {
-  return coverage::CovMapVersion::Version6;
+  // This should always be `CurrentVersion`, because that's the version LLVM
+  // will use when encoding the data we give it.
+  return coverage::CovMapVersion::CurrentVersion;
 }