Auto merge of #117484 - Zalathar:tests, r=cjgillot

coverage: Unify `tests/coverage-map` and `tests/run-coverage` into `tests/coverage`

Ever since the introduction of the `coverage-map` suite, it's been awkward to have to manage two separate coverage test directories containing dozens of mostly-identical files.

However, those two suites were separate for good reasons. They have very different requirements (since only one of them requires actually running the test program), running only one suite is noticeably faster than running both, and having separate suites allows them to be blessed separately if desired. So while unifying them was an obvious idea, actually doing so was non-trivial.

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Nevertheless, this PR finds a way to merge the two suites into one directory while retaining almost all of the developer-experience benefits of having two suites. This required non-trivial implementations of `Step`, but the end result works very smoothly.

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The first 5 commits are a copy of #117340, which has been closed in favour of this PR.

1 files changed, 139 insertions, 0 deletions

diff --git a/tests/coverage/async.coverage b/tests/coverage/async.coverage
new file mode 100644
index 00000000000..07bc16c2d92
--- /dev/null
+++ b/tests/coverage/async.coverage
@@ -0,0 +1,139 @@
+   LL|       |#![allow(unused_assignments, dead_code)]
+   LL|       |
+   LL|       |// compile-flags: --edition=2018 -C opt-level=1
+   LL|       |
+   LL|      1|async fn c(x: u8) -> u8 {
+   LL|      1|    if x == 8 {
+   LL|      1|        1
+   LL|       |    } else {
+   LL|      0|        0
+   LL|       |    }
+   LL|      1|}
+   LL|       |
+   LL|      0|async fn d() -> u8 { 1 }
+   LL|       |
+   LL|      0|async fn e() -> u8 { 1 } // unused function; executor does not block on `g()`
+   LL|       |
+   LL|      1|async fn f() -> u8 { 1 }
+   LL|       |
+   LL|      0|async fn foo() -> [bool; 10] { [false; 10] } // unused function; executor does not block on `h()`
+   LL|       |
+   LL|      1|pub async fn g(x: u8) {
+   LL|      0|    match x {
+   LL|      0|        y if e().await == y => (),
+   LL|      0|        y if f().await == y => (),
+   LL|      0|        _ => (),
+   LL|       |    }
+   LL|      0|}
+   LL|       |
+   LL|      1|async fn h(x: usize) { // The function signature is counted when called, but the body is not
+   LL|      0|                       // executed (not awaited) so the open brace has a `0` count (at least when
+   LL|      0|                       // displayed with `llvm-cov show` in color-mode).
+   LL|      0|    match x {
+   LL|      0|        y if foo().await[y] => (),
+   LL|      0|        _ => (),
+   LL|       |    }
+   LL|      0|}
+   LL|       |
+   LL|      1|async fn i(x: u8) { // line coverage is 1, but there are 2 regions:
+   LL|      1|                    // (a) the function signature, counted when the function is called; and
+   LL|      1|                    // (b) the open brace for the function body, counted once when the body is
+   LL|      1|                    // executed asynchronously.
+   LL|      1|    match x {
+   LL|      1|        y if c(x).await == y + 1 => { d().await; }
+                      ^0        ^0                  ^0  ^0
+   LL|      1|        y if f().await == y + 1 => (),
+                      ^0       ^0                ^0
+   LL|      1|        _ => (),
+   LL|       |    }
+   LL|      1|}
+   LL|       |
+   LL|      1|fn j(x: u8) {
+   LL|      1|    // non-async versions of `c()`, `d()`, and `f()` to make it similar to async `i()`.
+   LL|      1|    fn c(x: u8) -> u8 {
+   LL|      1|        if x == 8 {
+   LL|      1|            1 // This line appears covered, but the 1-character expression span covering the `1`
+                          ^0
+   LL|      1|              // is not executed. (`llvm-cov show` displays a `^0` below the `1` ). This is because
+   LL|      1|              // `fn j()` executes the open brace for the function body, followed by the function's
+   LL|      1|              // first executable statement, `match x`. Inner function declarations are not
+   LL|      1|              // "visible" to the MIR for `j()`, so the code region counts all lines between the
+   LL|      1|              // open brace and the first statement as executed, which is, in a sense, true.
+   LL|      1|              // `llvm-cov show` overcomes this kind of situation by showing the actual counts
+   LL|      1|              // of the enclosed coverages, (that is, the `1` expression was not executed, and
+   LL|      1|              // accurately displays a `0`).
+   LL|      1|        } else {
+   LL|      1|            0
+   LL|      1|        }
+   LL|      1|    }
+   LL|      1|    fn d() -> u8 { 1 } // inner function is defined in-line, but the function is not executed
+                  ^0
+   LL|      1|    fn f() -> u8 { 1 }
+   LL|      1|    match x {
+   LL|      1|        y if c(x) == y + 1 => { d(); }
+                      ^0                    ^0
+   LL|      1|        y if f() == y + 1 => (),
+                      ^0                   ^0
+   LL|      1|        _ => (),
+   LL|       |    }
+   LL|      1|}
+   LL|       |
+   LL|      0|fn k(x: u8) { // unused function
+   LL|      0|    match x {
+   LL|      0|        1 => (),
+   LL|      0|        2 => (),
+   LL|      0|        _ => (),
+   LL|       |    }
+   LL|      0|}
+   LL|       |
+   LL|      1|fn l(x: u8) {
+   LL|      1|    match x {
+   LL|      0|        1 => (),
+   LL|      0|        2 => (),
+   LL|      1|        _ => (),
+   LL|       |    }
+   LL|      1|}
+   LL|       |
+   LL|      1|async fn m(x: u8) -> u8 { x - 1 }
+                                      ^0
+   LL|       |
+   LL|      1|fn main() {
+   LL|      1|    let _ = g(10);
+   LL|      1|    let _ = h(9);
+   LL|      1|    let mut future = Box::pin(i(8));
+   LL|      1|    j(7);
+   LL|      1|    l(6);
+   LL|      1|    let _ = m(5);
+   LL|      1|    executor::block_on(future.as_mut());
+   LL|      1|}
+   LL|       |
+   LL|       |mod executor {
+   LL|       |    use core::{
+   LL|       |        future::Future,
+   LL|       |        pin::Pin,
+   LL|       |        task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
+   LL|       |    };
+   LL|       |
+   LL|      1|    pub fn block_on<F: Future>(mut future: F) -> F::Output {
+   LL|      1|        let mut future = unsafe { Pin::new_unchecked(&mut future) };
+   LL|      1|        use std::hint::unreachable_unchecked;
+   LL|      1|        static VTABLE: RawWakerVTable = RawWakerVTable::new(
+   LL|      1|            |_| unsafe { unreachable_unchecked() }, // clone
+                              ^0
+   LL|      1|            |_| unsafe { unreachable_unchecked() }, // wake
+                              ^0
+   LL|      1|            |_| unsafe { unreachable_unchecked() }, // wake_by_ref
+                              ^0
+   LL|      1|            |_| (),
+   LL|      1|        );
+   LL|      1|        let waker = unsafe { Waker::from_raw(RawWaker::new(core::ptr::null(), &VTABLE)) };
+   LL|      1|        let mut context = Context::from_waker(&waker);
+   LL|       |
+   LL|       |        loop {
+   LL|      1|            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {
+   LL|      1|                break val;
+   LL|      0|            }
+   LL|       |        }
+   LL|      1|    }
+   LL|       |}
+