Auto merge of #114843 - Zalathar:test-coverage-map, r=oli-obk

coverage: Explicitly test the coverage maps produced by codegen/LLVM

Our existing coverage tests verify the output of end-to-end coverage reports, but we don't have any way to test the specific mapping information (code regions and their associated counters) that are emitted by `rustc_codegen_llvm` and LLVM. That makes it harder to to be confident in changes that would modify those mappings (whether deliberately or accidentally).

This PR addresses that by adding a new `coverage-map` test suite that does the following:
- Compiles test files to LLVM IR assembly (`.ll`)
- Feeds those IR files to a custom tool (`src/tools/coverage-dump`) that extracts and decodes coverage mappings, and prints them in a more human-readable format
- Checks the output of that tool against known-good snapshots

---

I recommend excluding the last commit while reviewing the main changes, because that last commit is just ~40 test files copied over from `tests/run-coverage`, plus their blessed coverage-map snapshots and a readme file. Those snapshots aren't really intended to be checked by hand; they're mostly there to increase the chances that an unintended change to coverage maps will be observable (even if it requires relatively specific circumstances to manifest).

1 files changed, 57 insertions, 0 deletions

diff --git a/tests/coverage-map/status-quo/async2.rs b/tests/coverage-map/status-quo/async2.rs
new file mode 100644
index 00000000000..2884ff297af
--- /dev/null
+++ b/tests/coverage-map/status-quo/async2.rs
@@ -0,0 +1,57 @@
+// compile-flags: --edition=2018
+
+fn non_async_func() {
+    println!("non_async_func was covered");
+    let b = true;
+    if b {
+        println!("non_async_func println in block");
+    }
+}
+
+async fn async_func() {
+    println!("async_func was covered");
+    let b = true;
+    if b {
+        println!("async_func println in block");
+    }
+}
+
+async fn async_func_just_println() {
+    println!("async_func_just_println was covered");
+}
+
+fn main() {
+    println!("codecovsample::main");
+
+    non_async_func();
+
+    executor::block_on(async_func());
+    executor::block_on(async_func_just_println());
+}
+
+mod executor {
+    use core::{
+        future::Future,
+        pin::Pin,
+        task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
+    };
+
+    pub fn block_on<F: Future>(mut future: F) -> F::Output {
+        let mut future = unsafe { Pin::new_unchecked(&mut future) };
+        use std::hint::unreachable_unchecked;
+        static VTABLE: RawWakerVTable = RawWakerVTable::new(
+            |_| unsafe { unreachable_unchecked() }, // clone
+            |_| unsafe { unreachable_unchecked() }, // wake
+            |_| unsafe { unreachable_unchecked() }, // wake_by_ref
+            |_| (),
+        );
+        let waker = unsafe { Waker::from_raw(RawWaker::new(core::ptr::null(), &VTABLE)) };
+        let mut context = Context::from_waker(&waker);
+
+        loop {
+            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {
+                break val;
+            }
+        }
+    }
+}