Rollup merge of #156492 - RalfJung:cfg-miri, r=SimonSapin

remove/update various cfg(miri)

I went over all `cfg(miri)` in `library/`. Most of the things I noticed have become separate PRs; these here are the few remaining scattered little fixes in various places.

library/alloctests/tests/str.rs

@@ -2348,6 +2348,7 @@ fn utf8_char_counts() {
         .flat_map(|n| n - spread..=n + spread)
         .collect::<Vec<usize>>();
     if cfg!(not(miri)) {
+        // Miri is too slow
         reps.extend([1024, 1 << 16].iter().copied().flat_map(|n| n - spread..=n + spread));
     }
     let counts = if cfg!(miri) { 0..1 } else { 0..8 };

library/alloctests/tests/sync.rs

@@ -469,8 +469,6 @@ fn test_weak_count_locked() {
     while !a2.load(SeqCst) {
         let n = Arc::weak_count(&a2);
         assert!(n < 2, "bad weak count: {}", n);
-        #[cfg(miri)] // Miri's scheduler does not guarantee liveness, and thus needs this hint.
-        std::hint::spin_loop();
     }
     t.join().unwrap();
 }

library/std/src/sys/fs/unix.rs

@@ -1090,7 +1090,7 @@ pub fn metadata(&self) -> io::Result<FileAttr> {
             target_os = "illumos",
             target_vendor = "apple",
         )),
-        miri
+        miri // no dirfd on Miri
     ))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
         run_path_with_cstr(&self.path(), &lstat)

library/std/src/sys/pal/unix/conf.rs

@@ -12,9 +12,7 @@ pub fn page_size() -> usize {
 ///
 /// [posix_confstr]:
 ///     https://pubs.opengroup.org/onlinepubs/9699919799/functions/confstr.html
-//
-// FIXME: Support `confstr` in Miri.
-#[cfg(all(target_vendor = "apple", not(miri)))]
+#[cfg(target_vendor = "apple")]
 pub fn confstr(
     key: crate::ffi::c_int,
     size_hint: Option<usize>,

library/std/src/sys/pal/unix/conf/tests.rs

@@ -25,7 +25,7 @@ fn test_parse_glibc_version() {
 // Smoke check `confstr`, do it for several hint values, to ensure our resizing
 // logic is correct.
 #[test]
-#[cfg(all(target_vendor = "apple", not(miri)))]
+#[cfg(target_vendor = "apple")]
 fn test_confstr() {
     for key in [libc::_CS_DARWIN_USER_TEMP_DIR, libc::_CS_PATH] {
         let value_nohint = super::confstr(key, None).unwrap_or_else(|e| {

library/std/src/sys/pal/unix/mod.rs

@@ -78,7 +78,7 @@ unsafe fn sanitize_standard_fds() {
 
         // fast path with a single syscall for systems with poll()
         #[cfg(not(any(
-            miri,
+            miri, // no `poll`
             target_os = "emscripten",
             target_os = "fuchsia",
             target_os = "vxworks",
@@ -125,8 +125,6 @@ unsafe fn sanitize_standard_fds() {
 
         // fallback in case poll isn't available or limited by RLIMIT_NOFILE
         #[cfg(not(any(
-            // The standard fds are always available in Miri.
-            miri,
             target_os = "emscripten",
             target_os = "fuchsia",
             target_os = "vxworks",

library/std/src/sys/paths/unix.rs

@@ -393,7 +393,7 @@ pub fn current_exe() -> io::Result<PathBuf> {
     if !path.is_absolute() { getcwd().map(|cwd| cwd.join(path)) } else { Ok(path) }
 }
 
-#[cfg(all(target_vendor = "apple", not(miri)))]
+#[cfg(target_vendor = "apple")]
 fn darwin_temp_dir() -> PathBuf {
     crate::sys::pal::conf::confstr(libc::_CS_DARWIN_USER_TEMP_DIR, Some(64))
         .map(PathBuf::from)
@@ -407,7 +407,7 @@ fn darwin_temp_dir() -> PathBuf {
 pub fn temp_dir() -> PathBuf {
     crate::env::var_os("TMPDIR").map(PathBuf::from).unwrap_or_else(|| {
         cfg_select! {
-            all(target_vendor = "apple", not(miri)) => darwin_temp_dir(),
+            target_vendor = "apple" => darwin_temp_dir(),
             target_os = "android" => PathBuf::from("/data/local/tmp"),
             _ => PathBuf::from("/tmp"),
         }

library/std/tests/pipe_subprocess.rs

@@ -1,4 +1,5 @@
 fn main() {
+    // No `Command` on Miri and emscripten
     #[cfg(all(not(miri), any(unix, windows), not(target_os = "emscripten")))]
     {
         use std::io::{Read, pipe};

library/std/tests/windows_unix_socket.rs

@@ -1,5 +1,5 @@
 #![cfg(windows)]
-#![cfg(not(miri))] // no socket support in Miri
+#![cfg(not(miri))] // no Windows socket support in Miri
 #![feature(windows_unix_domain_sockets)]
 // Now only test windows_unix_domain_sockets feature
 // in the future, will test both unix and windows uds