parser: add error for typeof(T), suggesting typeof[T]() instead

vlib/v/parser/expr.v

@@ -223,6 +223,9 @@ fn (mut p Parser) check_expr(precedence int) !ast.Expr {
 				}
 			} else {
 				p.check(.lpar)
+				if p.tok.kind == .name && p.tok.lit.len > 0 && p.tok.lit[0].is_capital() {
+					p.error_with_pos('use `typeof[T]()`, instead of `typeof(T)`', spos)
+				}
 				expr := p.expr(0)
 				p.check(.rpar)
 				if p.tok.kind != .dot && p.tok.line_nr == p.prev_tok.line_nr {

vlib/v/parser/tests/typeof_typename_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/typeof_typename_err.vv:1:29: error: use `typeof[T]()`, instead of `typeof(T)`
+    1 | fn f[T]() { println("type ${typeof(T)}") }
+      |                             ~~~~~~
+    2 | f[int]()
+    3 | f[string]()

vlib/v/parser/tests/typeof_typename_err.vv

@@ -0,0 +1,5 @@
+fn f[T]() { println("type ${typeof(T)}") }
+f[int]()
+f[string]()
+
+