pref,builder: support -use-os-system-to-run to workaround segfaults using not fully updated xcode command line tools

Author: spytheman

vlib/v/builder/compile.v

@@ -134,26 +134,34 @@ fn (mut b Builder) run_compiled_executable_and_exit() {
 		run_args << ['run', compiled_file]
 	}
 	run_args << b.pref.run_args
-	mut run_process := os.new_process(run_file)
-	run_process.set_args(run_args)
 	if b.pref.is_verbose {
-		println('running ${run_process.filename} with arguments ${run_process.args}')
-	}
-	// Ignore sigint and sigquit while running the compiled file,
-	// so ^C doesn't prevent v from deleting the compiled file.
-	// See also https://git.musl-libc.org/cgit/musl/tree/src/process/system.c
-	prev_int_handler := os.signal_opt(.int, eshcb) or { serror('set .int', err) }
-	mut prev_quit_handler := os.SignalHandler(eshcb)
-	$if !windows { // There's no sigquit on windows
-		prev_quit_handler = os.signal_opt(.quit, eshcb) or { serror('set .quit', err) }
-	}
-	run_process.wait()
-	os.signal_opt(.int, prev_int_handler) or { serror('restore .int', err) }
-	$if !windows {
-		os.signal_opt(.quit, prev_quit_handler) or { serror('restore .quit', err) }
-	}
-	ret := run_process.code
-	run_process.close()
+		}
+		run_process.wait()
+		os.signal_opt(.int, prev_int_handler) or { serror('restore .int', err) }
+		$if !windows {
+			os.signal_opt(.quit, prev_quit_handler) or { serror('restore .quit', err) }
+		}
+		ret = run_process.code
+		run_process.close()
+	}
 	b.cleanup_run_executable_after_exit(compiled_file)
 	exit(ret)
 }

vlib/v/help/common/run.txt

@@ -15,4 +15,12 @@ The exit status of run will be:
 * `1` if the compilation failed.
 * The exit code of the compiled executable otherwise.
 
+Flags specific to `v run`:
+  -use-os-system-to-run
+     Use os.system() to run the produced executable, instead of os.new_process;
+     this is useful as a temporary workaround for segfaults, when running code
+     on macos, that may happen when xcode is updated after 2023/08/30, and for
+     comparing os.system with os.new_process on other systems. Usually used with:
+     `export VFLAGS='-use-os-system-to-run'`.
+
 For more about build flags, see `v help build`.

vlib/v/pref/pref.v

@@ -154,6 +154,7 @@ pub mut:
 	dump_files             string // `-dump-files files.txt` - let V store all V or .template file paths, that were used by the compiled program in `files.txt`, one path per line.
 	use_cache              bool   // when set, use cached modules to speed up subsequent compilations, at the cost of slower initial ones (while the modules are cached)
 	retry_compilation      bool = true // retry the compilation with another C compiler, if tcc fails.
+	use_os_system_to_run   bool   // when set, use os.system() to run the produced executable, instead of os.new_process; works around segfaults on macos, that may happen when xcode is updated
 	// TODO Convert this into a []string
 	cflags  string // Additional options which will be passed to the C compiler *before* other options.
 	ldflags string // Additional options which will be passed to the C compiler *after* everything else.
@@ -660,6 +661,9 @@ pub fn parse_args_and_show_errors(known_external_commands []string, args []strin
 			'-usecache' {
 				res.use_cache = true
 			}
+			'-use-os-system-to-run' {
+				res.use_os_system_to_run = true
+			}
 			'-nocache' {
 				res.use_cache = false
 			}