Rollup merge of #87602 - wesleywiser:partially_fix_short_backtraces_windows_optimized, r=dtolnay

[backtraces]: look for the `begin` symbol only after seeing `end`

On `x86_64-pc-windows-msvc`, we often get backtraces which look like
    this:

    ```
    10:     0x7ff77e0e9be5 - std::panicking::rust_panic_with_hook
    11:     0x7ff77e0e11b4 - std::sys_common::backtrace::__rust_begin_short_backtrace::h5769736bdb11136c
    12:     0x7ff77e0e116f - std::sys_common::backtrace::__rust_end_short_backtrace::h61c7ecb1b55338ae
    13:     0x7ff77e0f89dd - std::panicking::begin_panic::h8e60ef9f82a41805
    14:     0x7ff77e0e108c - d
    15:     0x7ff77e0e1069 - c
    16:     0x7ff77e0e1059 - b
    17:     0x7ff77e0e1049 - a
    18:     0x7ff77e0e1039 - core::ptr::drop_in_place<std::rt::lang_start<()>::{{closure}}>::h1bfcd14d5e15ba81
    19:     0x7ff77e0e1186 - std::sys_common::backtrace::__rust_begin_short_backtrace::h5769736bdb11136c
    20:     0x7ff77e0e100c - std::rt::lang_start::{{closure}}::ha054184bbf9921e3
    ```

Notice that `__rust_begin_short_backtrace` appears on frame 11 before
    `__rust_end_short_backtrace` on frame 12. This is because in typical
    release binaries without debug symbols, dbghelp.dll, which we use to walk
    and symbolize the stack, does not know where CGU internal functions
    start or end and so the closure invoked by `__rust_end_short_backtrace`
    is incorrectly described as `__rust_begin_short_backtrace` because it
    happens to be near that symbol.

While that can obviously change, this has been happening quite
    consistently since #75048. Since this is a very small change to the std
    and the change makes sense by itself, I think this is worth doing.

This doesn't completely resolve the situation for release binaries on
    Windows, since without debug symbols, the stack printed can still show
    incorrect symbol names (this is why the test uses `#[no_mangle]`) but it
    does slightly improve the situation in that you see the same backtrace
    you would see with `RUST_BACKTRACE=full` or in a debugger (without the
    uninteresting bits at the top and bottom).

Fixes part of #87481

Author: JohnTitor

library/std/src/sys_common/backtrace.rs

@@ -75,7 +75,7 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
             hit = true;
             if print_fmt == PrintFmt::Short {
                 if let Some(sym) = symbol.name().and_then(|s| s.as_str()) {
-                    if sym.contains("__rust_begin_short_backtrace") {
+                    if start && sym.contains("__rust_begin_short_backtrace") {
                         stop = true;
                         return;
                     }

src/test/ui/panics/panic-short-backtrace-windows-x86_64.rs

@@ -0,0 +1,49 @@
+// Regression test for #87481: short backtrace formatting cut off the entire stack trace.
+
+// Codegen-units is specified here so that we can replicate a typical rustc invocation which
+// is not normally limited to 1 CGU. This is important so that the `__rust_begin_short_backtrace`
+// and `__rust_end_short_backtrace` symbols are not marked internal to the CGU and thus will be
+// named in the symbol table.
+// compile-flags: -O -Ccodegen-units=8
+
+// run-fail
+// check-run-results
+// exec-env:RUST_BACKTRACE=1
+
+// We need to normalize out frame 5 because without debug info, dbghelp.dll doesn't know where CGU
+// internal functions like `main` start or end and so it will return whatever symbol happens
+// to be located near the address.
+// normalize-stderr-test: "5: .*" -> "5: some Rust fn"
+
+// Backtraces are pretty broken in general on i686-pc-windows-msvc (#62897).
+// only-x86_64-pc-windows-msvc
+
+fn main() {
+    a();
+}
+
+// Make these no_mangle so dbghelp.dll can figure out the symbol names.
+
+#[no_mangle]
+#[inline(never)]
+fn a() {
+    b();
+}
+
+#[no_mangle]
+#[inline(never)]
+fn b() {
+    c();
+}
+
+#[no_mangle]
+#[inline(never)]
+fn c() {
+    d();
+}
+
+#[no_mangle]
+#[inline(never)]
+fn d() {
+    panic!("d was called");
+}

src/test/ui/panics/panic-short-backtrace-windows-x86_64.run.stderr

@@ -0,0 +1,9 @@
+thread 'main' panicked at 'd was called', $DIR/panic-short-backtrace-windows-x86_64.rs:48:5
+stack backtrace:
+   0: std::panicking::begin_panic
+   1: d
+   2: c
+   3: b
+   4: a
+   5: some Rust fn
+note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.