Exit tests shouldn't emit crash logs. (#670)

When a process crashes, the platforms we support all write a crash log
(or core, or error report) to disk. This is not necessary for exit test
child processes (since we intentionally crash them.)

This PR suppresses generation of those logs from within an exit test:

- On Darwin, we disable the exception port for crash report files;
- On Linux, we set the maximum core dump size to zero bytes; and
- On Windows, we disable Windows Error Reporting.

The above effects are only applied to the exit test's child process, not
to the parent test process nor the system as a whole.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/ExitTests/ExitTest.swift

@@ -29,6 +29,39 @@ public struct ExitTest: Sendable {
   /// processes, so it can be used to uniquely identify an exit test at runtime.
   public var sourceLocation: SourceLocation
 
+  /// Disable crash reporting, crash logging, or core dumps for the current
+  /// process.
+  private static func _disableCrashReporting() {
+#if SWT_TARGET_OS_APPLE && !SWT_NO_MACH_PORTS
+    // We don't need to create a crash log (a "corpse notification") for an exit
+    // test. In the future, we might want to investigate actually setting up a
+    // listener port in the parent process and tracking interesting exceptions
+    // as separate exit conditions.
+    //
+    // BUG: The system may still opt to write crash logs to /Library/Logs
+    // instead of the user's home folder. rdar://47982238
+    _ = task_set_exception_ports(
+      swt_mach_task_self(),
+      exception_mask_t(EXC_MASK_CORPSE_NOTIFY),
+      mach_port_t(MACH_PORT_NULL),
+      EXCEPTION_DEFAULT,
+      THREAD_STATE_NONE
+    )
+#elseif os(Linux)
+    // On Linux, disable the generation of core files (although they will often
+    // be disabled by default.) If a particular Linux distro performs additional
+    // crash diagnostics, we may want to special-case them as well if we can.
+    var rl = rlimit(rlim_cur: 0, rlim_max: 0)
+    _ = setrlimit(CInt(RLIMIT_CORE.rawValue), &rl)
+#elseif os(Windows)
+    // On Windows, similarly disable Windows Error Reporting and the Windows
+    // Error Reporting UI. Note we expect to be the first component to call
+    // these functions, so we don't attempt to preserve any previously-set bits.
+    _ = SetErrorMode(UINT(SEM_NOGPFAULTERRORBOX))
+    _ = WerSetFlags(DWORD(WER_FAULT_REPORTING_NO_UI))
+#endif
+  }
+
   /// Call the exit test in the current process.
   ///
   /// This function invokes the closure originally passed to
@@ -37,6 +70,8 @@ public struct ExitTest: Sendable {
   /// terminate the process in a way that causes the corresponding expectation
   /// to fail.
   public func callAsFunction() async -> Never {
+    Self._disableCrashReporting()
+
     do {
       try await body()
     } catch {

Sources/_TestingInternals/include/Includes.h

@@ -39,7 +39,12 @@
 #include <string.h>
 #include <time.h>
 
-#if defined(__APPLE__) && __has_include(<dispatch/dispatch.h>)
+#if defined(__APPLE__) && !SWT_NO_MACH_PORTS
+#include <mach/mach_init.h>
+#include <mach/task.h>
+#endif
+
+#if defined(__APPLE__) && !SWT_NO_LIBDISPATCH
 #include <dispatch/dispatch.h>
 #endif
 
@@ -53,6 +58,10 @@
 #include <sys/fcntl.h>
 #endif
 
+#if __has_include(<sys/resource.h>)
+#include <sys/resource.h>
+#endif
+
 #if __has_include(<sys/stat.h>)
 #include <sys/stat.h>
 #endif

Sources/_TestingInternals/include/Stubs.h

@@ -64,6 +64,17 @@ static bool swt_S_ISFIFO(mode_t mode) {
 #endif
 #endif
 
+#if defined(__APPLE__) && !SWT_NO_MACH_PORTS
+/// Get a Mach port representing the current task (process.)
+///
+/// This function is provided because `mach_task_self()` is a complex macro, but
+/// directly accessing `mach_task_self_` from Swift triggers concurrency
+/// warnings about accessing shared mutable state.
+static mach_port_t swt_mach_task_self(void) {
+  return mach_task_self();
+}
+#endif
+
 #if defined(_WIN32)
 /// Make a Win32 language ID.
 ///