v: run code from stdin `echo println(2+2) | v run -`, with no repl limits (#6884)

cmd/v/help/run.txt

@@ -1,8 +1,11 @@
-Usage: v [build flags] run <file.v|directory> [arguments...]
+Usage: v [build flags] run <file.v|directory|-> [arguments...]
 
 This command is equivalent to running `v build` and running the compiled executable.
 The executable is passed the arguments as provided in [arguments...].
 
+If the target is '-', it means that the V source code to build comes from stdin.
+If the '-o' option is not specified, and the target is '-', a temporary base name for the executable will be used.
+
 The exit status of run will be:
 * `1` if the compilation failed.
 * The exit code of the compiled executable otherwise.

vlib/v/pref/pref.v

@@ -6,6 +6,7 @@ module pref
 import os.cmdline
 import os
 import v.vcache
+import rand
 
 pub enum BuildMode {
 	// `v program.v'
@@ -408,6 +409,44 @@ pub fn parse_args(args []string) (&Preferences, string) {
 		}
 		res.path = args[command_pos + 1]
 		res.run_args = args[command_pos + 2..]
+		if res.path == '-' {
+			tmp_file_path := rand.ulid()
+			mut tmp_exe_file_path := res.out_name
+			mut output_option := ''
+			if tmp_exe_file_path == '' {
+				tmp_exe_file_path = '${tmp_file_path}.exe'
+				output_option = '-o "$tmp_exe_file_path"'
+			}
+			tmp_v_file_path := '${tmp_file_path}.v'
+			mut lines := []string{}
+			for {
+				iline := os.get_raw_line()
+				if iline.len == 0 {
+					break
+				}
+				lines << iline
+			}
+			contents := lines.join('')
+			os.write_file(tmp_v_file_path, contents) or {
+				panic('Failed to create temporary file $tmp_v_file_path')
+			}
+			run_options := cmdline.options_before(args, ['run']).join(' ')
+			command_options := cmdline.options_after(args, ['run'])[1..].join(' ')
+			vexe := vexe_path()
+			tmp_cmd := '"$vexe" $output_option $run_options run "$tmp_v_file_path" $command_options'
+			//
+			res.vrun_elog('tmp_cmd: $tmp_cmd')
+			tmp_result := os.system(tmp_cmd)
+			res.vrun_elog('exit code: $tmp_result')
+			//
+			if output_option.len != 0 {
+				res.vrun_elog('remove tmp exe file: $tmp_exe_file_path')
+				os.rm(tmp_exe_file_path)
+			}
+			res.vrun_elog('remove tmp v file: $tmp_v_file_path')
+			os.rm(tmp_v_file_path)
+			exit(tmp_result)
+		}
 		must_exist(res.path)
 		if !res.path.ends_with('.v') && os.is_executable(res.path) && os.is_file(res.path) &&
 			os.is_file(res.path + '.v') {
@@ -430,6 +469,12 @@ pub fn parse_args(args []string) (&Preferences, string) {
 	return res, command
 }
 
+fn (pref &Preferences) vrun_elog(s string) {
+	if pref.is_verbose {
+		eprintln('> v run -, $s')
+	}
+}
+
 fn must_exist(path string) {
 	if !os.exists(path) {
 		eprintln('v expects that `$path` exists, but it does not')

vlib/v/tests/run_v_code_from_stdin_test.v

@@ -0,0 +1,23 @@
+import os
+
+const (
+	vexe = os.getenv('VEXE')
+)
+
+fn test_vexe_is_set() {
+	assert vexe != ''
+}
+
+fn test_pipe_to_v_run() ? {
+	cat_cmd := if os.user_os() == 'windows' { 'type' } else { 'cat' }
+	tmp_v_file := os.join_path(os.temp_dir(), 'generated_piped_program.v')
+	os.write_file(tmp_v_file, 'println(1 + 3)\nprintln("hello")\n') ?
+	assert os.is_file(tmp_v_file)
+	cmd := '"$cat_cmd" "$tmp_v_file" | "$vexe" run -'
+	res := os.exec(cmd) ?
+	// eprintln('>> cmd: $cmd | res: $res')
+	assert res.exit_code == 0
+	assert res.output.trim_space().split('\n') == ['4', 'hello']
+	os.rm(tmp_v_file)
+	assert !os.exists(tmp_v_file)
+}