Rollup merge of #135926 - jieyouxu:needs-subprocess-thread, r=oli-obk

Implement `needs-subprocess` directive, and cleanup a bunch of tests to use `needs-{subprocess,threads}`

### Summary

Closes #128295.

- Implements `//@ needs-subprocess` directive in compiletest as requested in #128295. However, compiletest is a host tool, so we can't just try to spawn process because that spawns the process on *host*, not the *target*, under cross-compilation scenarios.
    - The short-term solution is to add *Yet Another* list of allow-list targets.
    - The long-term solution is to first check if a `$target` supports std, then try to run a binary to do run-time capability detection *on the target*. But that is tricky because you have to build-and-run a binary *for the target*.
    - This PR picks the short-term solution, because the long-term solution is highly non-trivial, and it's already an improvement over individual `ignore-*`s all over the place.
    - Opened an issue about the long-term solution in #135928.
- Documents `//@ needs-subprocess` in rustc-dev-guide.
- Replace `ignore-{wasm,wasm32,emscripten,sgx}` with `needs-{subprocess,threads}` where suitable in tests.
- Some drive-by test changes as I was trying to figure out if I could use `needs-{subprocess,threads}` and found some bits needlessly distracting.

Count of tests that use `ignore-{wasm,wasm32,emscripten,sgx}` before and after this PR:

| State | `ignore-sgx` | `ignore-wasm` | `ignore-emscripten` |
| - | - | - | - |
| Before this PR | 96 | 88 | 207 |
| After this PR | 36 | 38 | 61 |

<details>
<summary>Commands used to find out locally</summary>

```
--- before

[17:40] Joe:rust (fresh) | rg --no-ignore -l "ignore-sgx" tests | wc -l
96
[17:40] Joe:rust (fresh) | rg --no-ignore -l "ignore-wasm" tests | wc -l
88
[17:40] Joe:rust (fresh) | rg --no-ignore -l "ignore-emscripten" tests | wc -l
207

--- after

[17:39] Joe:rust (needs-subprocess-thread) | rg --no-ignore -l "ignore-sgx" tests | wc -l
36
[17:39] Joe:rust (needs-subprocess-thread) | rg --no-ignore -l "ignore-wasm" tests | wc -l
38
[17:39] Joe:rust (needs-subprocess-thread) | rg --no-ignore -l "ignore-emscripten" tests | wc -l
61
```
</details>

### Review advice

- Best reviewed commit-by-commit.
- Non-trivial test changes (not mechanically simple replacements) are split into individual commits to help with review. Their individual commit messages give some basic description of the changes.
- I *could* split some test changes out into another PR, but I found that I needed to change some tests to `needs-threads`, some to `needs-subprocess`, and some needed to use *both*, so they might conflict and become very annoying.

---

r? ``@ghost`` (need to run try jobs)

try-job: x86_64-msvc-1
try-job: i686-msvc-1
try-job: i686-mingw
try-job: x86_64-mingw-1
try-job: x86_64-apple-1
try-job: aarch64-apple
try-job: aarch64-gnu
try-job: test-various
try-job: armhf-gnu

src/doc/rustc-dev-guide/src/tests/directives.md

@@ -94,7 +94,7 @@ for more details.
 | Directive                         | Explanation                                                                                                              | Supported test suites                        | Possible values                                                                         |
 |-----------------------------------|--------------------------------------------------------------------------------------------------------------------------|----------------------------------------------|-----------------------------------------------------------------------------------------|
 | `check-run-results`               | Check run test binary `run-{pass,fail}` output snapshot                                                                  | `ui`, `crashes`, `incremental` if `run-pass` | N/A                                                                                     |
-| `error-pattern`                   | Check that output contains a specific string                                                                             | `ui`, `crashes`, `incremental` if `run-pass` | String                                                                                   |
+| `error-pattern`                   | Check that output contains a specific string                                                                             | `ui`, `crashes`, `incremental` if `run-pass` | String                                                                                  |
 | `regex-error-pattern`             | Check that output contains a regex pattern                                                                               | `ui`, `crashes`, `incremental` if `run-pass` | Regex                                                                                   |
 | `check-stdout`                    | Check `stdout` against `error-pattern`s from running test binary[^check_stdout]                                          | `ui`, `crashes`, `incremental`               | N/A                                                                                     |
 | `normalize-stderr-32bit`          | Normalize actual stderr (for 32-bit platforms) with a rule `"<raw>" -> "<normalized>"` before comparing against snapshot | `ui`, `incremental`                          | `"<RAW>" -> "<NORMALIZED>"`, `<RAW>`/`<NORMALIZED>` is regex capture and replace syntax |
@@ -176,6 +176,7 @@ settings:
 - `needs-rust-lld` — ignores if the rust lld support is not enabled (`rust.lld =
   true` in `config.toml`)
 - `needs-threads` — ignores if the target does not have threading support
+- `needs-subprocess`  — ignores if the target does not have subprocess support
 - `needs-symlink` — ignores if the target does not support symlinks. This can be
   the case on Windows if the developer did not enable privileged symlink
   permissions.

src/tools/compiletest/src/common.rs

@@ -488,6 +488,17 @@ impl Config {
             git_merge_commit_email: &self.git_merge_commit_email,
         }
     }
+
+    pub fn has_subprocess_support(&self) -> bool {
+        // FIXME(#135928): compiletest is always a **host** tool. Building and running an
+        // capability detection executable against the **target** is not trivial. The short term
+        // solution here is to hard-code some targets to allow/deny, unfortunately.
+
+        let unsupported_target = self.target_cfg().env == "sgx"
+            || matches!(self.target_cfg().arch.as_str(), "wasm32" | "wasm64")
+            || self.target_cfg().os == "emscripten";
+        !unsupported_target
+    }
 }
 
 /// Known widths of `target_has_atomic`.

src/tools/compiletest/src/directive-list.rs

@@ -152,6 +152,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "needs-sanitizer-support",
     "needs-sanitizer-thread",
     "needs-std-debug-assertions",
+    "needs-subprocess",
     "needs-symlink",
     "needs-target-has-atomic",
     "needs-threads",

src/tools/compiletest/src/header/needs.rs

@@ -94,6 +94,11 @@ pub(super) fn handle_needs(
             condition: config.has_threads(),
             ignore_reason: "ignored on targets without threading support",
         },
+        Need {
+            name: "needs-subprocess",
+            condition: config.has_subprocess_support(),
+            ignore_reason: "ignored on targets without subprocess support",
+        },
         Need {
             name: "needs-unwind",
             condition: config.can_unwind(),
@@ -351,6 +356,9 @@ fn find_dlltool(config: &Config) -> bool {
     dlltool_found
 }
 
+// FIXME(#135928): this is actually not quite right because this detection is run on the **host**.
+// This however still helps the case of windows -> windows local development in case symlinks are
+// not available.
 #[cfg(windows)]
 fn has_symlinks() -> bool {
     if std::env::var_os("CI").is_some() {

src/tools/tidy/src/issues.txt

@@ -2204,7 +2204,6 @@ ui/issues/issue-3895.rs
 ui/issues/issue-38954.rs
 ui/issues/issue-38987.rs
 ui/issues/issue-39089.rs
-ui/issues/issue-39175.rs
 ui/issues/issue-39211.rs
 ui/issues/issue-39367.rs
 ui/issues/issue-39548.rs

src/tools/tidy/src/ui_tests.rs

@@ -17,7 +17,7 @@ use ignore::Walk;
 const ENTRY_LIMIT: u32 = 901;
 // FIXME: The following limits should be reduced eventually.
 
-const ISSUES_ENTRY_LIMIT: u32 = 1664;
+const ISSUES_ENTRY_LIMIT: u32 = 1662;
 
 const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
     "rs",     // test source files

tests/ui/abi/homogenous-floats-target-feature-mixup.rs

@@ -5,8 +5,7 @@
 // without #[repr(simd)]
 
 //@ run-pass
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 
 #![feature(avx512_target_feature)]
 

tests/ui/abi/segfault-no-out-of-stack.rs

@@ -1,6 +1,5 @@
 //@ run-pass
-//@ ignore-wasm32 can't run commands
-//@ ignore-sgx no processes
+//@ needs-subprocess
 //@ ignore-fuchsia must translate zircon signal to SIGSEGV/SIGBUS, FIXME (#58590)
 
 #![feature(rustc_private)]

tests/ui/abi/stack-probes-lto.rs

@@ -3,7 +3,7 @@
 //@[aarch64] only-aarch64
 //@[x32] only-x86
 //@[x64] only-x86_64
-//@ ignore-sgx no processes
+//@ needs-subprocess
 //@ ignore-musl FIXME #31506
 //@ ignore-fuchsia no exception handler registered for segfault
 //@ compile-flags: -C lto

tests/ui/abi/stack-probes.rs

@@ -3,8 +3,7 @@
 //@[aarch64] only-aarch64
 //@[x32] only-x86
 //@[x64] only-x86_64
-//@ ignore-emscripten no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 //@ ignore-fuchsia no exception handler registered for segfault
 //@ ignore-nto Crash analysis impossible at SIGSEGV in QNX Neutrino
 //@ ignore-ios Stack probes are enabled, but the SIGSEGV handler isn't

tests/ui/alloc-error/default-alloc-error-hook.rs

@@ -1,6 +1,5 @@
 //@ run-pass
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 
 use std::alloc::{Layout, handle_alloc_error};
 use std::env;

tests/ui/array-slice-vec/bounds-check-no-overflow.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:index out of bounds
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::mem::size_of;
 

tests/ui/array-slice-vec/box-of-array-of-drop-1.rs

@@ -1,12 +1,12 @@
 //@ run-pass
 //@ needs-unwind
+//@ needs-threads
+
 #![allow(overflowing_literals)]
 
 // Test that we cleanup a fixed size Box<[D; k]> properly when D has a
 // destructor.
 
-//@ ignore-emscripten no threads support
-
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};
 

tests/ui/array-slice-vec/box-of-array-of-drop-2.rs

@@ -1,12 +1,12 @@
 //@ run-pass
 //@ needs-unwind
+//@ needs-threads
+
 #![allow(overflowing_literals)]
 
 // Test that we cleanup dynamic sized Box<[D]> properly when D has a
 // destructor.
 
-//@ ignore-emscripten no threads support
-
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};
 

tests/ui/array-slice-vec/dst-raw-slice.rs

@@ -2,7 +2,7 @@
 
 //@ run-fail
 //@ error-pattern:index out of bounds
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #[allow(unconditional_panic)]
 fn main() {

tests/ui/array-slice-vec/nested-vec-3.rs

@@ -1,8 +1,8 @@
 //@ run-pass
 //@ needs-unwind
-#![allow(overflowing_literals)]
+//@ needs-threads
 
-//@ ignore-emscripten no threads support
+#![allow(overflowing_literals)]
 
 // Test that using the `vec!` macro nested within itself works when
 // the contents implement Drop and we hit a panic in the middle of

tests/ui/array-slice-vec/slice-panic-1.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // Test that if a slicing expr[..] fails, the correct cleanups happen.
 

tests/ui/array-slice-vec/slice-panic-2.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // Test that if a slicing expr[..] fails, the correct cleanups happen.
 

tests/ui/array-slice-vec/vec-overrun.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:index out of bounds: the len is 1 but the index is 2
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let v: Vec<isize> = vec![10];

tests/ui/backtrace/backtrace.rs

@@ -1,8 +1,7 @@
 //@ run-pass
 //@ ignore-android FIXME #17520
-//@ ignore-wasm32 spawning processes is not supported
+//@ needs-subprocess
 //@ ignore-openbsd no support for libbacktrace without filename
-//@ ignore-sgx no processes
 //@ ignore-msvc see #62897 and `backtrace-debuginfo.rs` test
 //@ ignore-fuchsia Backtraces not symbolized
 //@ compile-flags:-g

tests/ui/backtrace/std-backtrace.rs

@@ -1,8 +1,7 @@
 //@ run-pass
 //@ ignore-android FIXME #17520
-//@ ignore-wasm32 spawning processes is not supported
+//@ needs-subprocess
 //@ ignore-openbsd no support for libbacktrace without filename
-//@ ignore-sgx no processes
 //@ ignore-fuchsia Backtraces not symbolized
 //@ compile-flags:-g
 //@ compile-flags:-Cstrip=none

tests/ui/binop/binop-fail-3.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:quux
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn foo() -> ! {
     panic!("quux");

tests/ui/binop/binop-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:quux
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn my_err(s: String) -> ! {
     println!("{}", s);

tests/ui/borrowck/borrowck-local-borrow.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:panic 1
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let x = 2;

tests/ui/borrowck/issue-28934.rs

@@ -3,7 +3,7 @@
 
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 struct Parser<'i: 't, 't>(&'i u8, &'t u8);
 

tests/ui/box/unit/unwind-unique.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 use std::thread;
 

tests/ui/cleanup-rvalue-temp-during-incomplete-alloc.rs

@@ -20,7 +20,7 @@
 // It's unclear how likely such a bug is to recur, but it seems like a
 // scenario worth testing.
 
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 use std::thread;
 

tests/ui/closures/diverging-closure.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:oops
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let func = || -> ! {

tests/ui/command/command-argv0.rs

@@ -1,8 +1,7 @@
 //@ run-pass
 
-//@ ignore-windows - this is a unix-specific test
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ only-unix (this is a unix-specific test)
+//@ needs-subprocess
 use std::env;
 use std::os::unix::process::CommandExt;
 use std::process::Command;

tests/ui/command/command-current-dir.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 //@ no-prefer-dynamic We move the binary around, so do not depend dynamically on libstd
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 //@ ignore-fuchsia Needs directory creation privilege
 
 use std::env;

tests/ui/command/command-exec.rs

@@ -1,13 +1,9 @@
 //@ run-pass
 
-#![allow(stable_features)]
-//@ ignore-windows - this is a unix-specific test
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ only-unix (this is a unix-specific test)
+//@ needs-subprocess
 //@ ignore-fuchsia no execvp syscall provided
 
-#![feature(process_exec)]
-
 use std::env;
 use std::os::unix::process::CommandExt;
 use std::process::Command;

tests/ui/command/command-pre-exec.rs

@@ -1,11 +1,9 @@
 //@ run-pass
-
-#![allow(stable_features)]
-//@ ignore-windows - this is a unix-specific test
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ only-unix (this is a unix-specific test)
+//@ needs-subprocess
 //@ ignore-fuchsia no execvp syscall
-#![feature(process_exec, rustc_private)]
+
+#![feature(rustc_private)]
 
 extern crate libc;
 

tests/ui/command/command-setgroups.rs

@@ -1,9 +1,8 @@
 //@ run-pass
-//@ ignore-windows - this is a unix-specific test
-//@ ignore-wasm32
-//@ ignore-sgx
+//@ only-unix (this is a unix-specific test)
 //@ ignore-musl - returns dummy result for _SC_NGROUPS_MAX
 //@ ignore-nto - does not have `/bin/id`, expects groups to be i32 (not u32)
+//@ needs-subprocess
 
 #![feature(rustc_private)]
 #![feature(setgroups)]

tests/ui/command/command-uid-gid.rs

@@ -1,8 +1,7 @@
 //@ run-pass
 //@ ignore-android
-//@ ignore-emscripten
-//@ ignore-sgx
 //@ ignore-fuchsia no '/bin/sh', '/bin/ls'
+//@ needs-subprocess
 
 #![feature(rustc_private)]
 

tests/ui/command/issue-10626.rs

@@ -1,6 +1,5 @@
 //@ run-pass
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 
 // Make sure that if a process doesn't have its stdio/stderr descriptors set up
 // that we don't die in a large ball of fire

tests/ui/consts/issue-29798.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:index out of bounds: the len is 5 but the index is 5
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 const fn test(x: usize) -> i32 {
     [42;5][x]

tests/ui/coroutine/coroutine-resume-after-panic.rs

@@ -1,7 +1,7 @@
 //@ run-fail
 //@ needs-unwind
 //@ error-pattern:coroutine resumed after panicking
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 // Test that we get the correct message for resuming a panicked coroutine.
 

tests/ui/drop/drop-trait-enum.rs

@@ -2,7 +2,7 @@
 #![allow(dead_code)]
 #![allow(unused_assignments)]
 #![allow(unused_variables)]
-//@ ignore-emscripten no threads support
+//@ needs-threads
 //@ needs-unwind
 
 use std::thread;

tests/ui/drop/terminate-in-initializer.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // Issue #787
 // Don't try to clean up uninitialized locals

tests/ui/expr/if/expr-if-panic-fn.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn f() -> ! {
     panic!()

tests/ui/expr/if/expr-if-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let _x = if false {

tests/ui/expr/if/if-check-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:Number is odd
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn even(x: usize) -> bool {
     if x < 2 {

tests/ui/expr/if/if-cond-bot.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:quux
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn my_err(s: String) -> ! {
     println!("{}", s);

tests/ui/extern/issue-18576.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:stop
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 // #18576
 // Make sure that calling an extern function pointer in an unreachable

tests/ui/extern/issue-64655-allow-unwind-when-calling-panic-directly.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // rust-lang/rust#64655: with panic=unwind, a panic from a subroutine
 // should still run destructors as it unwinds the stack. However,

tests/ui/extern/issue-64655-extern-rust-must-allow-unwind.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // rust-lang/rust#64655: with panic=unwind, a panic from a subroutine
 // should still run destructors as it unwinds the stack. However,

tests/ui/fn/expr-fn-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn f() -> ! {
     panic!()

tests/ui/hashmap/hashmap-capacity-overflow.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:capacity overflow
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::collections::hash_map::HashMap;
 use std::mem::size_of;

tests/ui/imports/glob-use-std.rs

@@ -2,7 +2,7 @@
 
 //@ run-fail
 //@ error-pattern:panic works
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::*;
 

tests/ui/intrinsics/panic-uninitialized-zeroed.rs

@@ -1,11 +1,10 @@
+// ignore-tidy-linelength
+//! This test checks panic emitted from `mem::{uninitialized,zeroed}`.
 //@ run-pass
 //@ revisions: default strict
 //@ [strict]compile-flags: -Zstrict-init-checks
-// ignore-tidy-linelength
-//@ ignore-wasm32 spawning processes is not supported
-//@ ignore-sgx no processes
-//
-// This test checks panic emitted from `mem::{uninitialized,zeroed}`.
+//@ needs-subprocess
+
 #![allow(deprecated, invalid_value)]
 #![feature(never_type)]
 

tests/ui/issues/issue-12920.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 pub fn main() {
     panic!();

tests/ui/issues/issue-13202.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:bad input
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     Some("foo").unwrap_or(panic!("bad input")).to_string();

tests/ui/issues/issue-20971.rs

@@ -2,7 +2,7 @@
 
 //@ run-fail
 //@ error-pattern:Hello, world!
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 pub trait Parser {
     type Input;

tests/ui/issues/issue-2190-1.rs

@@ -1,20 +1,16 @@
-//@ run-pass
-#![allow(unused_must_use)]
-#![allow(non_upper_case_globals)]
-
-//@ ignore-emscripten no threads
+//@ check-pass
 
 use std::thread::Builder;
 
-static generations: usize = 1024+256+128+49;
+static GENERATIONS: usize = 1024+256+128+49;
 
 fn spawn(mut f: Box<dyn FnMut() + 'static + Send>) {
-    Builder::new().stack_size(32 * 1024).spawn(move|| f());
+    Builder::new().stack_size(32 * 1024).spawn(move || f());
 }
 
 fn child_no(x: usize) -> Box<dyn FnMut() + 'static + Send> {
-    Box::new(move|| {
-        if x < generations {
+    Box::new(move || {
+        if x < GENERATIONS {
             spawn(child_no(x+1));
         }
     })

tests/ui/issues/issue-23354-2.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:panic evaluated
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #[allow(unused_variables)]
 fn main() {

tests/ui/issues/issue-23354.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:panic evaluated
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #[allow(unused_variables)]
 fn main() {

tests/ui/issues/issue-2470-bounds-check-overflow.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:index out of bounds
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::mem;
 

tests/ui/issues/issue-25089.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 use std::thread;
 

tests/ui/issues/issue-26655.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 // Check that the destructors of simple enums are run on unwinding
 

tests/ui/issues/issue-2761.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:custom message
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert!(false, "custom message");

tests/ui/issues/issue-29485.rs

@@ -2,7 +2,7 @@
 #![allow(unused_attributes)]
 //@ aux-build:issue-29485.rs
 //@ needs-unwind
-//@ ignore-emscripten no threads
+//@ needs-threads
 
 #[feature(recover)]
 

tests/ui/issues/issue-30018-panic.rs

@@ -5,7 +5,7 @@
 // SIGTRAP injected by the drop-flag consistency checking.
 
 //@ needs-unwind
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 struct Foo;
 

tests/ui/issues/issue-3029.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:so long
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #![allow(unreachable_code)]
 

tests/ui/issues/issue-30380.rs

@@ -3,7 +3,7 @@
 
 //@ run-fail
 //@ error-pattern:panicking destructors ftw!
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 struct Observer<'a>(&'a mut FilledOnDrop);
 

tests/ui/issues/issue-33770.rs

@@ -1,6 +1,5 @@
 //@ run-pass
-//@ ignore-wasm32 no processes
-//@ ignore-sgx no processes
+//@ needs-subprocess
 
 use std::process::{Command, Stdio};
 use std::env;

tests/ui/issues/issue-38763.rs

@@ -1,5 +1,5 @@
 //@ run-pass
-//@ ignore-emscripten
+//@ needs-threads
 
 #[repr(C)]
 pub struct Foo(i128);

tests/ui/issues/issue-44216-add-system-time.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:overflow
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::time::{Duration, SystemTime};
 

tests/ui/issues/issue-44216-sub-instant.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:overflow
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::time::{Instant, Duration};
 

tests/ui/issues/issue-44216-sub-system-time.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:overflow
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 use std::time::{Duration, SystemTime};
 

tests/ui/lifetimes/tail-expr-lock-poisoning.rs

@@ -1,5 +1,6 @@
 //@ revisions: edition2021 edition2024
-//@ ignore-wasm no panic or subprocess support
+//@ ignore-wasm no panic support
+//@ needs-subprocess
 //@ [edition2024] edition: 2024
 //@ run-pass
 //@ needs-unwind

tests/ui/loops/for-each-loop-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:moop
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     for _ in 0_usize..10_usize {

tests/ui/macros/assert-as-macro.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:assertion failed: 1 == 2
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert!(1 == 2);

tests/ui/macros/assert-eq-macro-msg.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:assertion `left == right` failed: 1 + 1 definitely should be 3
 //@ error-pattern:  left: 2
 //@ error-pattern: right: 3
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert_eq!(1 + 1, 3, "1 + 1 definitely should be 3");

tests/ui/macros/assert-eq-macro-panic.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:assertion `left == right` failed
 //@ error-pattern:  left: 14
 //@ error-pattern: right: 15
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert_eq!(14, 15);

tests/ui/macros/assert-macro-explicit.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:assertion failed: false
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert!(false);

tests/ui/macros/assert-macro-fmt.rs

@@ -1,7 +1,7 @@
 //@ run-fail
 //@ error-pattern: panicked
 //@ error-pattern: test-assert-fmt 42 rust
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert!(false, "test-assert-fmt {} {}", 42, "rust");

tests/ui/macros/assert-macro-owned.rs

@@ -1,7 +1,7 @@
 //@ run-fail
 //@ error-pattern:panicked
 //@ error-pattern:test-assert-owned
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #![allow(non_fmt_panics)]
 

tests/ui/macros/assert-macro-static.rs

@@ -1,7 +1,7 @@
 //@ run-fail
 //@ error-pattern:panicked
 //@ error-pattern:test-assert-static
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert!(false, "test-assert-static");

tests/ui/macros/assert-matches-macro-msg.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:assertion `left matches right` failed: 1 + 1 definitely should be 3
 //@ error-pattern:  left: 2
 //@ error-pattern: right: 3
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #![feature(assert_matches)]
 

tests/ui/macros/assert-ne-macro-msg.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:assertion `left != right` failed: 1 + 1 definitely should not be 2
 //@ error-pattern:  left: 2
 //@ error-pattern: right: 2
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert_ne!(1 + 1, 2, "1 + 1 definitely should not be 2");

tests/ui/macros/assert-ne-macro-panic.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:assertion `left != right` failed
 //@ error-pattern:  left: 14
 //@ error-pattern: right: 14
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     assert_ne!(14, 14);

tests/ui/macros/die-macro-2.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:test
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     panic!("test");

tests/ui/macros/die-macro-expr.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:test
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let __isize: isize = panic!("test");

tests/ui/macros/die-macro-pure.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:test
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn f() {
     panic!("test");

tests/ui/macros/unimplemented-macro-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:not implemented
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     unimplemented!()

tests/ui/macros/unreachable-arg.rs

@@ -1,4 +1,4 @@
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 //@ revisions: edition_2015 edition_2021
 //@ [edition_2015]edition:2015

tests/ui/macros/unreachable-fmt-msg.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:internal error: entered unreachable code: 6 is not prime
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     unreachable!("{} is not {}", 6u32, "prime");

tests/ui/macros/unreachable-format-arg.rs

@@ -1,5 +1,5 @@
 //@ run-fail
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 //@ revisions: edition_2015 edition_2021
 //@ [edition_2015]edition:2015

tests/ui/macros/unreachable-format-args.rs

@@ -1,4 +1,4 @@
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 //@ revisions: edition_2015 edition_2021
 //@ [edition_2015]edition:2015

tests/ui/macros/unreachable-macro-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:internal error: entered unreachable code
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     unreachable!()

tests/ui/macros/unreachable-static-msg.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:internal error: entered unreachable code: uhoh
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     unreachable!("uhoh")

tests/ui/macros/unreachable.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:internal error: entered unreachable code
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     unreachable!()

tests/ui/match/expr-match-panic-fn.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn f() -> ! {
     panic!()

tests/ui/match/expr-match-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn main() {
     let _x = match true {

tests/ui/match/match-bot-panic.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:explicit panic
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #![allow(unreachable_code)]
 #![allow(unused_variables)]

tests/ui/match/match-disc-bot.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:quux
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn f() -> ! {
     panic!("quux")

tests/ui/match/match-wildcards.rs

@@ -1,6 +1,6 @@
 //@ run-fail
 //@ error-pattern:squirrelcupcake
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 fn cmp() -> isize {
     match (Some('a'), None::<char>) {

tests/ui/meta/revision-ok.rs

@@ -5,7 +5,7 @@
 //@ revisions: foo bar
 //@[foo] error-pattern:foo
 //@[bar] error-pattern:bar
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 #[cfg(foo)]
 fn die() {

tests/ui/mir/mir_codegen_calls_converging_drops.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:converging_fn called
 //@ error-pattern:0 dropped
 //@ error-pattern:exit
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 struct Droppable(u8);
 impl Drop for Droppable {

tests/ui/mir/mir_codegen_calls_converging_drops_2.rs

@@ -2,7 +2,7 @@
 //@ error-pattern:complex called
 //@ error-pattern:dropped
 //@ error-pattern:exit
-//@ ignore-emscripten no processes
+//@ needs-subprocess
 
 struct Droppable;
 impl Drop for Droppable {