jsgen: improve handling of `blank_ident`

vlib/v/gen/js/js.v

@@ -672,7 +672,11 @@ fn (mut g JsGen) gen_assign_stmt(it ast.AssignStmt) {
 		// multi return
 		g.write('const [')
 		for i, ident in it.left {
+			if ident.name in ['', '_'] {
+				g.write('')
+			} else {
 				g.write(g.js_name(ident.name))
+			}
 			if i < it.left.len - 1 {
 				g.write(', ')
 			}
@@ -684,6 +688,16 @@ fn (mut g JsGen) gen_assign_stmt(it ast.AssignStmt) {
 		// `a := 1` | `a,b := 1,2`
 		for i, ident in it.left {
 			val := it.right[i]
+
+			if ident.kind == .blank_ident || ident.name in ['', '_'] {
+				tmp_var := g.new_tmp_var()
+				// TODO: Can the tmp_var declaration be omitted?
+				g.write('const $tmp_var = ')
+				g.expr(val)
+				g.writeln(';')
+				continue
+			}
+
 			ident_var_info := ident.var_info()
 			mut styp := g.typ(ident_var_info.typ)
 
@@ -898,7 +912,9 @@ fn (mut g JsGen) gen_for_c_stmt(it ast.ForCStmt) {
 fn (mut g JsGen) gen_for_in_stmt(it ast.ForInStmt) {
 	if it.is_range {
 		// `for x in 1..10 {`
-		i := it.val_var
+		mut i := it.val_var
+		if i in ['', '_'] { i = g.new_tmp_var() }
+
 		g.inside_loop = true
 		g.write('for (let $i = ')
 		g.expr(it.cond)
@@ -908,43 +924,34 @@ fn (mut g JsGen) gen_for_in_stmt(it ast.ForInStmt) {
 		g.inside_loop = false
 		g.stmts(it.stmts)
 		g.writeln('}')
-	} else if it.kind == .array || it.cond_type.has_flag(.variadic) {
+	} else if it.kind in [.array, .string] || it.cond_type.has_flag(.variadic) {
 		// `for num in nums {`
-		i := if it.key_var == '' { g.new_tmp_var() } else { it.key_var }
+		i := if it.key_var in ['', '_'] { g.new_tmp_var() } else { it.key_var }
+		val := if it.val_var in ['', '_'] { '' } else { it.val_var }
 		// styp := g.typ(it.val_type)
 		g.inside_loop = true
 		g.write('for (let $i = 0; $i < ')
 		g.expr(it.cond)
 		g.writeln('.length; ++$i) {')
 		g.inside_loop = false
-		g.write('\tlet $it.val_var = ')
+		if val !in ['', '_'] {
+			g.write('\tconst $val = ')
 			g.expr(it.cond)
 			g.writeln('[$i];')
+		}
 		g.stmts(it.stmts)
 		g.writeln('}')
 	} else if it.kind == .map {
 		// `for key, val in map[string]int {`
 		// key_styp := g.typ(it.key_type)
 		// val_styp := g.typ(it.val_type)
-		key := if it.key_var == '' { g.new_tmp_var() } else { it.key_var }
+		key := if it.key_var in ['', '_'] { '' } else { it.key_var }
-		g.write('for (let [$key, $it.val_var] of ')
+		val := if it.val_var in ['', '_'] { '' } else { it.val_var }
+		g.write('for (let [$key, $val] of ')
 		g.expr(it.cond)
 		g.writeln(') {')
 		g.stmts(it.stmts)
 		g.writeln('}')
-	} else if it.kind == .string {
-		// `for x in 'hello' {`
-		i := if it.key_var == '' { g.new_tmp_var() } else { it.key_var }
-		g.inside_loop = true
-		g.write('for (let $i = 0; $i < ')
-		g.expr(it.cond)
-		g.writeln('.length; ++$i) {')
-		g.inside_loop = false
-		g.write('\tlet $it.val_var = ')
-		g.expr(it.cond)
-		g.writeln('[$i];')
-		g.stmts(it.stmts)
-		g.writeln('}')
 	}
 }
 
@@ -1081,6 +1088,14 @@ fn (mut g JsGen) gen_array_init_expr(it ast.ArrayInit) {
 }
 
 fn (mut g JsGen) gen_assign_expr(it ast.AssignExpr) {
+	if it.left_type == table.void_type && it.op == .assign {
+		// _ = 1
+		tmp_var := g.new_tmp_var()
+		g.write('const $tmp_var = ')
+		g.expr(it.val)
+	}
+
+	// NB: The expr has to go *before* inside_map_set as it's defined there
 	g.expr(it.left)
 	if g.inside_map_set && it.op == .assign {
 		g.inside_map_set = false
@@ -1120,7 +1135,10 @@ fn (mut g JsGen) gen_call_expr(it ast.CallExpr) {
 }
 
 fn (mut g JsGen) gen_ident(node ast.Ident) {
-	name := g.js_name(node.name)
+	mut name := g.js_name(node.name)
+	if node.kind == .blank_ident || name in ['', '_']{
+		name = g.new_tmp_var()
+	}
 	// TODO `is`
 	// TODO handle optionals
 	g.write(name)

vlib/v/gen/js/tests/array.js

@@ -1,5 +1,5 @@
-// V_COMMIT_HASH 2943bdc
+// V_COMMIT_HASH 808975f
-// V_CURRENT_COMMIT_HASH ad5deef
+// V_CURRENT_COMMIT_HASH 564545d
 // Generated by the V compiler
 
 "use strict";
@@ -27,7 +27,7 @@ const builtin = (function () {
 	/* module exports */
 	return {
 		println,
-		print,
+		print
 	};
 })();
 
@@ -73,11 +73,14 @@ const main = (function () {
 		arr2.push(6);
 		arr2.push(...[7, 8, 9]);
 		builtin.println(arr2);
+		builtin.println("\n\n");
 		/** @type {string} */
 		let slice4 = idx1.slice(0, 4);
+		builtin.print("Back\t=> ");
 		builtin.println(slice4);
 		/** @type {number} */
-		const idx2 = slice4.charCodeAt(0);
+		const idx2 = "😀".charCodeAt(0);
+		builtin.print("66\t=> ");
 		builtin.println(idx2);
 		/** @type {Map<string, string>} */
 		let m = new Map();
@@ -86,11 +89,30 @@ const main = (function () {
 		m.set(key, "value");
 		/** @type {string} */
 		const val = m.get("key");
+		builtin.print("value\t=> ");
 		builtin.println(val);
+		builtin.print("true\t=> ");
 		builtin.println(arr1.includes("JS"));
+		builtin.print("false\t=> ");
 		builtin.println(!(arr2.includes(3)));
+		builtin.print("true\t=> ");
 		builtin.println(m.has("key"));
+		builtin.print("true\t=> ");
 		builtin.println(!(m.has("badkey")));
+		for (let _tmp1 = 0; _tmp1 < arr1.length; ++_tmp1) {
+		}
+		
+		builtin.println("0 to 8\t=>");
+		for (let i = 0; i < arr2.length; ++i) {
+			builtin.println(i);
+		}
+		
+		builtin.println("\n\n4 to 5\t=> ");
+		for (let _tmp2 = 0; _tmp2 < slice3.length; ++_tmp2) {
+			const v = slice3[_tmp2];
+			builtin.println(v);
+		}
+		
 	})();
 
 	/* module exports */

vlib/v/gen/js/tests/array.v

@@ -32,13 +32,16 @@ println(arr2)
 arr2 << 6
 arr2 << [7, 8, 9]
 println(arr2)
+println('\n\n')
 
 // String slices
 mut slice4 := idx1[..4]
+print('Back\t=> ')
 println(slice4) // 'Back'
 
 // String indexes
 idx2 := slice4[0]
+print('66\t=> ')
 println(idx2)
 // TODO:
 // slice4[3] = `c`
@@ -48,10 +51,22 @@ mut m := map[string]string
 key := 'key'
 m[key] = 'value'
 val := m['key']
+print('value\t=> ')
 println(val)
 
 // 'in' / '!in'
+print('true\t=> ')
 println('JS' in arr1)
+print('false\t=> ')
 println(3 !in arr2)
+print('true\t=> ')
 println('key' in m)
+print('true\t=> ')
 println('badkey' !in m)
+
+// for in
+for _ in arr1 {}
+println('0 to 8\t=>')
+for i, _ in arr2 { println(i) }
+println('\n\n4 to 5\t=> ')
+for _, v in slice3 { println(v) }

vlib/v/gen/js/tests/js.js

@@ -1,5 +1,5 @@
-// V_COMMIT_HASH 11e6734
+// V_COMMIT_HASH 808975f
-// V_CURRENT_COMMIT_HASH 99c70cf
+// V_CURRENT_COMMIT_HASH 564545d
 // Generated by the V compiler
 
 "use strict";
@@ -27,7 +27,7 @@ const builtin = (function () {
 	/* module exports */
 	return {
 		println,
-		print,
+		print
 	};
 })();
 
@@ -106,7 +106,7 @@ const hello = (function () {
 		Aaa,
 		Ccc,
 		v_debugger,
-		excited,
+		excited
 	};
 })();
 
@@ -182,6 +182,7 @@ const main = (function (hl) {
 	function v_class(v_extends, v_instanceof) {
 		/** @type {number} */
 		const v_delete = v_instanceof;
+		const _tmp1 = v_delete;
 	}
 	
 	/* program entry point */
@@ -203,17 +204,13 @@ const main = (function (hl) {
 		});
 		c.a.update("another update");
 		builtin.println(c);
-		/** @type {string} */
+		const _tmp2 = "done";
-		const v = "done";
 		{
-			/** @type {string} */
+			const _tmp3 = "block";
-			const _ = "block";
 		}
 		
-		/** @type {number} */
+		const _tmp4 = POSITION.go_back;
-		const pos = POSITION.go_back;
+		const _tmp5 = hl.Ccc.a;
-		/** @type {number} */
-		const enum2 = hl.Ccc.a;
 		/** @type {string} */
 		const v_debugger = "JS keywords";
 		/** @type {string} */
@@ -237,8 +234,8 @@ const main = (function (hl) {
 		
 		/** @type {number[]} */
 		const arr = [1, 2, 3, 4, 5];
-		for (let _tmp1 = 0; _tmp1 < arr.length; ++_tmp1) {
+		for (let _tmp6 = 0; _tmp6 < arr.length; ++_tmp6) {
-			let i = arr[_tmp1];
+			let i = arr[_tmp6];
 		}
 		
 		/** @type {Map<string, string>} */
@@ -296,8 +293,8 @@ const main = (function (hl) {
 	 * @returns {[number, number]}
 	*/
 	function hello(game_on, ...dummy) {
-		for (let _tmp2 = 0; _tmp2 < dummy.length; ++_tmp2) {
+		for (let _tmp7 = 0; _tmp7 < dummy.length; ++_tmp7) {
-			let dd = dummy[_tmp2];
+			let dd = dummy[_tmp7];
 			/** @type {string} */
 			const l = dd;
 		}

vlib/v/gen/js/tests/js.v

@@ -26,6 +26,7 @@ enum POSITION {
 
 fn class(extends string, instanceof int) {
     delete := instanceof
+    _ = delete
 }
 
 
@@ -46,13 +47,13 @@ fn main() {
     c.a.update('another update')
     println(c)
 
-    v := "done"
+    _ := "done"
     {
         _ = "block"
     }
 
-    pos := POSITION.go_back
+    _ = POSITION.go_back
-    enum2 := hl.Ccc.a
+    _ = hl.Ccc.a
 
     debugger := 'JS keywords'
     // TODO: Implement interpolation

vlib/v/tests/blank_ident_test.v

@@ -258,3 +258,17 @@ fn test_nested_for_in_string_both() {
 		}
 	}
 }
+
+fn multi_return() (int, int, string) {
+	return 1, 2, '3'
+}
+
+fn test_blank_multi_return() {
+	_, a, b := multi_return()
+	c, _, d := multi_return()
+	e, f, _ := multi_return()
+	_, _, g := multi_return()
+	_, h, _ := multi_return()
+	i, _, _ := multi_return()
+	_, _, _ := multi_return()
+}