1 files changed, 100 insertions, 0 deletions
diff --git a/tests/run-make/coverage/lib/used_crate.rs b/tests/run-make/coverage/lib/used_crate.rs
new file mode 100644
index 000000000..8b8b1f7f3
--- /dev/null
+++ b/tests/run-make/coverage/lib/used_crate.rs
@@ -0,0 +1,100 @@
+#![allow(unused_assignments, unused_variables)]
+// compile-flags: -C opt-level=3 # validates coverage now works with optimizations
+use std::fmt::Debug;
+
+pub fn used_function() {
+    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    // dependent conditions.
+    let is_true = std::env::args().len() == 1;
+    let mut countdown = 0;
+    if is_true {
+        countdown = 10;
+    }
+    use_this_lib_crate();
+}
+
+pub fn used_only_from_bin_crate_generic_function<T: Debug>(arg: T) {
+    println!("used_only_from_bin_crate_generic_function with {:?}", arg);
+}
+// Expect for above function: `Unexecuted instantiation` (see below)
+pub fn used_only_from_this_lib_crate_generic_function<T: Debug>(arg: T) {
+    println!("used_only_from_this_lib_crate_generic_function with {:?}", arg);
+}
+
+pub fn used_from_bin_crate_and_lib_crate_generic_function<T: Debug>(arg: T) {
+    println!("used_from_bin_crate_and_lib_crate_generic_function with {:?}", arg);
+}
+
+pub fn used_with_same_type_from_bin_crate_and_lib_crate_generic_function<T: Debug>(arg: T) {
+    println!("used_with_same_type_from_bin_crate_and_lib_crate_generic_function with {:?}", arg);
+}
+
+pub fn unused_generic_function<T: Debug>(arg: T) {
+    println!("unused_generic_function with {:?}", arg);
+}
+
+pub fn unused_function() {
+    let is_true = std::env::args().len() == 1;
+    let mut countdown = 2;
+    if !is_true {
+        countdown = 20;
+    }
+}
+
+fn unused_private_function() {
+    let is_true = std::env::args().len() == 1;
+    let mut countdown = 2;
+    if !is_true {
+        countdown = 20;
+    }
+}
+
+fn use_this_lib_crate() {
+    used_from_bin_crate_and_lib_crate_generic_function("used from library used_crate.rs");
+    used_with_same_type_from_bin_crate_and_lib_crate_generic_function(
+        "used from library used_crate.rs",
+    );
+    let some_vec = vec![5, 6, 7, 8];
+    used_only_from_this_lib_crate_generic_function(some_vec);
+    used_only_from_this_lib_crate_generic_function("used ONLY from library used_crate.rs");
+}
+
+// FIXME(#79651): "Unexecuted instantiation" errors appear in coverage results,
+// for example:
+//
+// | Unexecuted instantiation: used_crate::used_only_from_bin_crate_generic_function::<_>
+//
+// These notices appear when `llvm-cov` shows instantiations. This may be a
+// default option, but it can be suppressed with:
+//
+// ```shell
+// $ `llvm-cov show --show-instantiations=0 ...`
+// ```
+//
+// The notice is triggered because the function is unused by the library itself,
+// and when the library is compiled, a synthetic function is generated, so
+// unused function coverage can be reported. Coverage can be skipped for unused
+// generic functions with:
+//
+// ```shell
+// $ `rustc -Zunstable-options -C instrument-coverage=except-unused-generics ...`
+// ```
+//
+// Even though this function is used by `uses_crate.rs` (and
+// counted), with substitutions for `T`, those instantiations are only generated
+// when the generic function is actually used (from the binary, not from this
+// library crate). So the test result shows coverage for all instantiated
+// versions and their generic type substitutions, plus the `Unexecuted
+// instantiation` message for the non-substituted version. This is valid, but
+// unfortunately a little confusing.
+//
+// The library crate has its own coverage map, and the only way to show unused
+// coverage of a generic function is to include the generic function in the
+// coverage map, marked as an "unused function". If the library were used by
+// another binary that never used this generic function, then it would be valid
+// to show the unused generic, with unknown substitution (`_`).
+//
+// The alternative is to exclude all generics from being included in the "unused
+// functions" list, which would then omit coverage results for
+// `unused_generic_function<T>()`, below.