tests: add vlib/v/gen/js/program_test.v to ease regression testing `-b js` programs

vlib/v/gen/js/jsgen_test.v

@@ -2,7 +2,7 @@ import os
 
 const (
 	test_dir     = os.join_path('vlib', 'v', 'gen', 'js', 'tests')
-	output_dir   = '_js_tests/'
+	output_dir   = os.join_path(os.temp_dir(), '_js_tests/')
 	v_options    = '-b js -w'
 	node_options = ''
 )

vlib/v/gen/js/program_test.v

@@ -0,0 +1,98 @@
+import os
+import term
+import rand
+import v.util.vtest
+import v.util.diff
+
+const vexe = @VEXE
+
+const vroot = @VMODROOT
+
+const diff_cmd = find_diff_cmd()
+
+fn find_diff_cmd() string {
+	return diff.find_working_diff_command() or { '' }
+}
+
+[noreturn]
+fn exit_because(msg string) {
+	eprintln('$msg, tests will not run')
+	exit(0)
+}
+
+fn test_node_exists() {
+	res := os.execute('node --version')
+	if res.exit_code != 0 {
+		exit_because('node does not exist')
+	}
+	if !res.output.starts_with('v') {
+		exit_because('invalid node version')
+	}
+	version := res.output.trim_left('v').int()
+	if version < 10 {
+		exit_because('node should be at least version 10, but is currently version: $version')
+	}
+	println('Using node version: $version')
+}
+
+fn test_running_programs_compiled_with_the_js_backend() ? {
+	os.setenv('VCOLORS', 'never', true)
+	os.chdir(vroot)
+	test_dir := 'vlib/v/gen/js/tests/testdata'
+	main_files := get_main_files_in_dir(test_dir)
+	fails := check_path(test_dir, main_files) ?
+	assert fails == 0
+}
+
+fn get_main_files_in_dir(dir string) []string {
+	mut mfiles := os.walk_ext(dir, '.v')
+	mfiles.sort()
+	return mfiles
+}
+
+fn check_path(dir string, tests []string) ?int {
+	mut nb_fail := 0
+	paths := vtest.filter_vtest_only(tests, basepath: vroot)
+	for path in paths {
+		program := path.replace(vroot + os.path_separator, '')
+		program_out := program.replace('.v', '.out')
+		if !os.exists(program_out) {
+			os.write_file(program_out, '') ?
+		}
+		print(program + ' ')
+		res := os.execute('$vexe -b js run $program')
+		if res.exit_code < 0 {
+			panic(res.output)
+		}
+		mut expected := os.read_file(program_out) ?
+		expected = clean_line_endings(expected)
+		found := clean_line_endings(res.output)
+		if expected != found {
+			println(term.red('FAIL'))
+			println('============')
+			println('expected $program_out content:')
+			println(expected)
+			println('============')
+			println('found:')
+			println(found)
+			println('============\n')
+			println('diff:')
+			println(diff.color_compare_strings(diff_cmd, rand.ulid(), found, expected))
+			println('============\n')
+			nb_fail++
+		} else {
+			println(term.green('OK'))
+			assert true
+		}
+	}
+	return nb_fail
+}
+
+fn clean_line_endings(s string) string {
+	mut res := s.trim_space()
+	res = res.replace(' \n', '\n')
+	res = res.replace(' \r\n', '\n')
+	res = res.replace('\r\n', '\n')
+	res = res.trim('\n')
+	return res
+}

vlib/v/gen/js/tests/testdata/compare_ints.out

@@ -0,0 +1 @@
+2 > 1

vlib/v/gen/js/tests/testdata/compare_ints.v

@@ -0,0 +1,15 @@
+if 2 > 1 {
+	println('2 > 1')
+}
+
+if 2 < 1 {
+	println('2 < 1')
+}
+
+if 2 == 1 {
+	println('2 == 1')
+}
+
+if 2 == 0 {
+	println('2 == 0')
+}

vlib/v/gen/js/tests/testdata/hw.out

@@ -0,0 +1 @@
+hello world

vlib/v/gen/js/tests/testdata/hw.v

@@ -0,0 +1 @@
+println('hello world')