js: support JS.await (#12726)

cmd/tools/vtest.v

@@ -114,6 +114,9 @@ fn should_test(path string, backend string) ShouldTestStatus {
 	if path.ends_with('_test.v') {
 		return .test
 	}
+	if path.ends_with('_test.js.v') {
+		return .test
+	}
 	if path.ends_with('.v') && path.count('.') == 2 {
 		if !path.all_before_last('.v').all_before_last('.').ends_with('_test') {
 			return .ignore

vlib/v/ast/ast.v

@@ -485,6 +485,7 @@ pub mut:
 	return_type_pos   token.Position // `string` in `fn (u User) name() string` position
 	has_return        bool
 	should_be_skipped bool
+	has_await         bool           // 'true' if this function uses JS.await
 	//
 	comments      []Comment // comments *after* the header, but *before* `{`; used for InterfaceDecl
 	next_comments []Comment // coments that are one line after the decl; used for InterfaceDecl

vlib/v/checker/checker.v

@@ -2550,6 +2550,35 @@ pub fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool)
 			c.need_recheck_generic_fns = true
 		}
 	}
+	if fn_name == 'JS.await' {
+		if node.args.len > 1 {
+			c.error('JS.await expects 1 argument, a promise value (e.g `JS.await(fs.read())`',
+				node.pos)
+			return ast.void_type
+		}
+
+		typ := c.expr(node.args[0].expr)
+		tsym := c.table.get_type_symbol(typ)
+
+		if !tsym.name.starts_with('js.promise.Promise<') {
+			c.error('JS.await: first argument must be a promise, got `$tsym.name`', node.pos)
+			return ast.void_type
+		}
+		c.table.cur_fn.has_await = true
+		match tsym.info {
+			ast.Struct {
+				mut ret_type := tsym.info.concrete_types[0]
+				ret_type = ret_type.set_flag(.optional)
+				node.return_type = ret_type
+				return ret_type
+			}
+			else {
+				c.error('JS.await: Promise must be a struct type', node.pos)
+				return ast.void_type
+			}
+		}
+		panic('unreachable')
+	}
 	if fn_name == 'json.encode' {
 	} else if fn_name == 'json.decode' && node.args.len > 0 {
 		if node.args.len != 2 {

vlib/v/gen/js/fn.v

@@ -66,14 +66,25 @@ fn (mut g JsGen) js_call(node ast.CallExpr) {
 	g.call_stack << node
 	it := node
 	call_return_is_optional := it.return_type.has_flag(.optional)
+	is_await := node.name == 'JS.await'
 	if call_return_is_optional {
+		if is_await {
+			g.writeln('await (async function () {')
+		} else {
 			g.writeln('(function () {')
+		}
 		g.writeln('try {')
 		g.writeln('let tmp = ')
 	}
 	if it.is_ctor_new {
 		g.write('new ')
 	}
+	if is_await {
+		g.write('await (')
+
+		g.expr(it.args[0].expr)
+		g.write(').promise')
+	} else {
 		g.write('${g.js_mname(it.name)}(')
 		for i, arg in it.args {
 			g.expr(arg.expr)
@@ -83,6 +94,7 @@ fn (mut g JsGen) js_call(node ast.CallExpr) {
 		}
 		// end call
 		g.write(')')
+	}
 	if call_return_is_optional {
 		g.write(';\n')
 		g.writeln('if (tmp === null) throw "none";')
@@ -588,18 +600,20 @@ fn (mut g JsGen) gen_method_decl(it ast.FnDecl, typ FnGenType) {
 		g.writeln('${g.typ(it.receiver.typ)}.prototype.$it.name = ')
 	}
 
-	has_go := fn_has_go(it)
-
+	mut has_go := fn_has_go(it) || it.has_await
+	for attr in it.attrs {
+		if attr.name == 'async' {
+			has_go = true
+			break
+		}
+	}
 	is_main := it.name == 'main.main'
 	g.gen_attrs(it.attrs)
 	if is_main {
 		// there is no concept of main in JS but we do have iife
 		g.writeln('/* program entry point */')
-
-		// g.write('(')
-		if has_go {
+		// main function is always async
 		g.write('async ')
-		}
 		g.write('function js_main(')
 	} else if it.is_anon {
 		g.write('function (')

vlib/v/gen/js/js.v

@@ -321,6 +321,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 	if g.pref.sourcemap {
 		out += g.create_sourcemap()
 	}
+
 	return out
 }
 
@@ -335,7 +336,7 @@ fn (g JsGen) create_sourcemap() string {
 
 pub fn (mut g JsGen) gen_js_main_for_tests() {
 	g.enter_namespace('main')
-	g.writeln('function js_main() {  ')
+	g.writeln('async function js_main() {  ')
 	g.inc_indent()
 	all_tfuncs := g.get_all_test_function_names()
 
@@ -351,7 +352,7 @@ pub fn (mut g JsGen) gen_js_main_for_tests() {
 			g.writeln('main__BenchedTests_testing_step_start(bt,new string("$tcname"))')
 		}
 
-		g.writeln('try { ${tcname}(); } catch (_e) {} ')
+		g.writeln('try { let res = ${tcname}(); if (res instanceof Promise) { await res; } } catch (_e) {} ')
 		if g.pref.is_stats {
 			g.writeln('main__BenchedTests_testing_step_end(bt);')
 		}