Auto merge of #124507 - Zalathar:coverage-level, r=compiler-errors

coverage: Replace boolean options with a `CoverageLevel` enum

After #123409, and some discussion at https://github.com/rust-lang/rust/issues/79649#issuecomment-2042093553 and #124120, it became clear to me that we should have a unified concept of “coverage level”, instead of having several separate boolean flags that aren't actually independent.

This PR therefore introduces a `CoverageLevel` enum, to replace the existing boolean flags for `branch` and `mcdc`.

The `no-branch` value (for `-Zcoverage-options`) has been renamed to `block`, instructing the compiler to only instrument for block coverage, with no branch coverage or MD/DC instrumentation.

`@rustbot` label +A-code-coverage
cc `@ZhuUx` `@Lambdaris` `@RenjiSann`

1 files changed, 20 insertions, 4 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 4f259960ac3..a3978cc14a4 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -146,10 +146,26 @@ pub enum InstrumentCoverage {
 /// Individual flag values controlled by `-Z coverage-options`.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Default)]
 pub struct CoverageOptions {
-    /// Add branch coverage instrumentation.
-    pub branch: bool,
-    /// Add mcdc coverage instrumentation.
-    pub mcdc: bool,
+    pub level: CoverageLevel,
+    // Other boolean or enum-valued options might be added here.
+}
+
+/// Controls whether branch coverage or MC/DC coverage is enabled.
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum CoverageLevel {
+    /// Instrument for coverage at the MIR block level.
+    Block,
+    /// Also instrument branch points (includes block coverage).
+    Branch,
+    /// Instrument for MC/DC. Mostly a superset of branch coverage, but might
+    /// differ in some corner cases.
+    Mcdc,
+}
+
+impl Default for CoverageLevel {
+    fn default() -> Self {
+        Self::Block
+    }
 }
 
 /// Settings for `-Z instrument-xray` flag.