darwin: expose ptrace with errno handling

lib/std/os.zig

@@ -42,6 +42,7 @@ pub const uefi = @import("os/uefi.zig");
 pub const wasi = @import("os/wasi.zig");
 pub const windows = @import("os/windows.zig");
 pub const posix_spawn = @import("os/posix_spawn.zig");
+pub const ptrace = @import("os/ptrace.zig");
 
 comptime {
     assert(@import("std") == std); // std lib tests require --zig-lib-dir

lib/std/os/ptrace.zig

@@ -0,0 +1,28 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+const os = @import("../os.zig");
+const system = os.system;
+const errno = system.getErrno;
+const pid_t = system.pid_t;
+const unexpectedErrno = os.unexpectedErrno;
+const UnexpectedError = os.UnexpectedError;
+
+pub usingnamespace ptrace;
+
+const ptrace = if (builtin.target.isDarwin()) struct {
+    pub const PtraceError = error{
+        ProcessNotFound,
+        PermissionDenied,
+    } || UnexpectedError;
+
+    pub fn ptrace(request: i32, pid: pid_t) PtraceError!void {
+        switch (errno(system.ptrace(request, pid, null, 0))) {
+            .SUCCESS => return,
+            .SRCH => return error.ProcessNotFound,
+            .INVAL => unreachable,
+            .BUSY, .PERM => return error.PermissionDenied,
+            else => |err| return unexpectedErrno(err),
+        }
+    }
+} else struct {};