tools: prevent v init from overwriting an already existing src/main.v file (fix #17362) (#17363)

cmd/tools/vcreate/vcreate.v

@@ -133,10 +133,11 @@ fn init_project() {
 		c.write_vmod(false)
 		println('Change the description of your project in `v.mod`')
 	}
-
+	if !os.exists('src/main.v') {
-	c.files << ProjectFiles{
+		c.files << ProjectFiles{
-		path: 'src/main.v'
+			path: 'src/main.v'
-		content: hello_world_content()
+			content: hello_world_content()
+		}
 	}
 	c.create_files_and_directories()
 	c.write_gitattributes(false)

cmd/tools/vcreate/vcreate_test.v

@@ -7,19 +7,30 @@ const test_path = os.join_path(os.vtmp_dir(), 'v', 'test_vcreate')
 
 fn init_and_check() ! {
 	os.chdir(test_path)!
+
+	// if main file already exist we should not tamper it
+	mut main_last_modified_time := i64(0)
+	is_main_file_preexisting := os.exists('src/main.v')
+	if is_main_file_preexisting == true {
+		main_last_modified_time = os.file_last_mod_unix('src/main.v')
+	}
 	os.execute_or_exit('${os.quoted_path(@VEXE)} init')
 
 	x := os.execute_or_exit('${os.quoted_path(@VEXE)} run .')
 	assert x.exit_code == 0
 	assert x.output.trim_space() == 'Hello World!'
 
-	assert os.read_file('src/main.v')! == [
+	if is_main_file_preexisting == true {
-		'module main\n',
+		assert main_last_modified_time == os.file_last_mod_unix('src/main.v')
-		'fn main() {',
+	} else {
-		"	println('Hello World!')",
+		assert os.read_file('src/main.v')! == [
-		'}',
+			'module main\n',
-		'',
+			'fn main() {',
-	].join_lines()
+			"	println('Hello World!')",
+			'}',
+			'',
+		].join_lines()
+	}
 
 	assert os.read_file('v.mod')! == [
 		'Module {',