Rollup merge of #116094 - Swatinem:coverage-branch-gate, r=wesleywiser

Introduce `-C instrument-coverage=branch` to gate branch coverage

This was extracted from https://github.com/rust-lang/rust/pull/115061 and can land independently from other coverage related work.

The flag is unused for now, but is added in advance of adding branch coverage support.
It is an unstable, nightly only flag that needs to be used in combination with `-Zunstable-options`, like so: `-Zunstable-options -C instrument-coverage=branch`.

The goal is to develop branch coverage as an unstable opt-in feature first, before it matures and can be turned on by default.

7 files changed, 19 insertions, 6 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 462e7e85c65..84933588f17 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -169,6 +169,9 @@ pub enum MirSpanview {
 pub enum InstrumentCoverage {
     /// Default `-C instrument-coverage` or `-C instrument-coverage=statement`
     All,
+    /// Additionally, instrument branches and output branch coverage.
+    /// `-Zunstable-options -C instrument-coverage=branch`
+    Branch,
     /// `-Zunstable-options -C instrument-coverage=except-unused-generics`
     ExceptUnusedGenerics,
     /// `-Zunstable-options -C instrument-coverage=except-unused-functions`
@@ -2747,7 +2750,10 @@ pub fn build_session_options(
         }
         (Some(InstrumentCoverage::Off | InstrumentCoverage::All), _) => {}
         (Some(_), _) if !unstable_opts.unstable_options => {
-            handler.early_error("`-C instrument-coverage=except-*` requires `-Z unstable-options`");
+            handler.early_error(
+                "`-C instrument-coverage=branch` and `-C instrument-coverage=except-*` \
+                require `-Z unstable-options`",
+            );
         }
         (None, None) => {}
         (None, ic) => {
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index c090bcaf9d8..77aaf951f0d 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -389,7 +389,7 @@ mod desc {
     pub const parse_mir_spanview: &str = "`statement` (default), `terminator`, or `block`";
     pub const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub const parse_instrument_coverage: &str =
-        "`all` (default), `except-unused-generics`, `except-unused-functions`, or `off`";
+        "`all` (default), `branch`, `except-unused-generics`, `except-unused-functions`, or `off`";
     pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
     pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
@@ -931,6 +931,7 @@ mod parse {
 
         *slot = Some(match v {
             "all" => InstrumentCoverage::All,
+            "branch" => InstrumentCoverage::Branch,
             "except-unused-generics" | "except_unused_generics" => {
                 InstrumentCoverage::ExceptUnusedGenerics
             }
@@ -1356,6 +1357,7 @@ options! {
         reports (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`. Optional values are:
         `=all` (implicit value)
+        `=branch`
         `=except-unused-generics`
         `=except-unused-functions`
         `=off` (default)"),
@@ -1597,6 +1599,7 @@ options! {
         reports (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`. Optional values are:
         `=all` (implicit value)
+        `=branch`
         `=except-unused-generics`
         `=except-unused-functions`
         `=off` (default)"),
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 79307498165..94fe38b72ad 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -702,6 +702,10 @@ impl Session {
         self.opts.cg.instrument_coverage() != InstrumentCoverage::Off
     }
 
+    pub fn instrument_coverage_branch(&self) -> bool {
+        self.opts.cg.instrument_coverage() == InstrumentCoverage::Branch
+    }
+
     pub fn instrument_coverage_except_unused_generics(&self) -> bool {
         self.opts.cg.instrument_coverage() == InstrumentCoverage::ExceptUnusedGenerics
     }
diff --git a/tests/ui/instrument-coverage/bad-value.bad.stderr b/tests/ui/instrument-coverage/bad-value.bad.stderr
index 246c4f31a4b..b867d169dae 100644
--- a/tests/ui/instrument-coverage/bad-value.bad.stderr
+++ b/tests/ui/instrument-coverage/bad-value.bad.stderr
@@ -1,2 +1,2 @@
-error: incorrect value `bad-value` for codegen option `instrument-coverage` - `all` (default), `except-unused-generics`, `except-unused-functions`, or `off` was expected
+error: incorrect value `bad-value` for codegen option `instrument-coverage` - `all` (default), `branch`, `except-unused-generics`, `except-unused-functions`, or `off` was expected
 
diff --git a/tests/ui/instrument-coverage/bad-value.blank.stderr b/tests/ui/instrument-coverage/bad-value.blank.stderr
index b539c558d9b..e7122fb61cd 100644
--- a/tests/ui/instrument-coverage/bad-value.blank.stderr
+++ b/tests/ui/instrument-coverage/bad-value.blank.stderr
@@ -1,2 +1,2 @@
-error: incorrect value `` for codegen option `instrument-coverage` - `all` (default), `except-unused-generics`, `except-unused-functions`, or `off` was expected
+error: incorrect value `` for codegen option `instrument-coverage` - `all` (default), `branch`, `except-unused-generics`, `except-unused-functions`, or `off` was expected
 
diff --git a/tests/ui/instrument-coverage/except-unused-functions.stderr b/tests/ui/instrument-coverage/except-unused-functions.stderr
index 82c1c630cbf..acc633a2a6d 100644
--- a/tests/ui/instrument-coverage/except-unused-functions.stderr
+++ b/tests/ui/instrument-coverage/except-unused-functions.stderr
@@ -1,2 +1,2 @@
-error: `-C instrument-coverage=except-*` requires `-Z unstable-options`
+error: `-C instrument-coverage=branch` and `-C instrument-coverage=except-*` require `-Z unstable-options`
 
diff --git a/tests/ui/instrument-coverage/except-unused-generics.stderr b/tests/ui/instrument-coverage/except-unused-generics.stderr
index 82c1c630cbf..acc633a2a6d 100644
--- a/tests/ui/instrument-coverage/except-unused-generics.stderr
+++ b/tests/ui/instrument-coverage/except-unused-generics.stderr
@@ -1,2 +1,2 @@
-error: `-C instrument-coverage=except-*` requires `-Z unstable-options`
+error: `-C instrument-coverage=branch` and `-C instrument-coverage=except-*` require `-Z unstable-options`