pref: allow running a .vsh script with just `v build.vsh gcc`, instead of `v run build.vsh gcc` (#12409)

cmd/v/v.v

@@ -79,7 +79,7 @@ fn main() {
 		util.launch_tool(false, 'vrepl', os.args[1..])
 		return
 	}
-	args_and_flags := util.join_env_vflags_and_os_args()[1..]
+	mut args_and_flags := util.join_env_vflags_and_os_args()[1..]
 	prefs, command := pref.parse_args(external_tools, args_and_flags)
 	if prefs.use_cache && os.user_os() == 'windows' {
 		eprintln('-usecache is currently disabled on windows')

vlib/v/pref/pref.v

@@ -697,6 +697,14 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 	if !res.is_bare && res.bare_builtin_dir != '' {
 		eprintln('`-bare-builtin-dir` must be used with `-freestanding`')
 	}
+	if command.ends_with('.vsh') {
+		// `v build.vsh gcc` is the same as `v run build.vsh gcc`,
+		// i.e. compiling, then running the script, passing the args
+		// after it to the script:
+		res.is_run = true
+		res.path = command
+		res.run_args = args[command_pos + 1..]
+	}
 	if command == 'build-module' {
 		res.build_mode = .build_module
 		if command_pos + 1 >= args.len {

vlib/v/tests/vsh_envbang_test.v

@@ -0,0 +1,36 @@
+import os
+import rand
+
+fn test_envbang_script_runs() ? {
+	env_location := '/usr/bin/env'
+	$if windows {
+		skip_test('windows does not support envbang lines')
+	}
+	if !os.exists(env_location) {
+		skip_test('$env_location does not exist')
+	}
+	if !os.is_executable(env_location) {
+		skip_test('$env_location is not executable')
+	}
+	os.find_abs_path_of_executable('v') or { skip_test('v is not in PATH') }
+	rndname := rand.ulid()
+	rnd_vsh_script_path := os.real_path(os.join_path(os.cache_dir(), '${rndname}.vsh'))
+	os.write_file(rnd_vsh_script_path, "#!$env_location v
+import os
+println('hello')
+println(os.args)
+") ?
+	os.chmod(rnd_vsh_script_path, 0o700) ?
+	res := os.execute('"$rnd_vsh_script_path" abc 123 -option')
+	assert res.exit_code == 0
+	lines := res.output.split_into_lines()
+	assert lines[0] == 'hello'
+	assert lines[1].ends_with(", 'abc', '123', '-option']")
+	os.rm(rnd_vsh_script_path) ?
+}
+
+[noreturn]
+fn skip_test(reason string) {
+	println('skipping test, because $reason .')
+	exit(0)
+}