checker: show errors for index calls to values which are not functions, fixes #11539 (#12024)

vlib/v/checker/checker.v

@@ -2811,19 +2811,29 @@ pub fn (mut c Checker) fn_call(mut node ast.CallExpr) ast.Type {
 			elem_typ := c.table.get_type_symbol(info.elem_type)
 			if elem_typ.info is ast.FnType {
 				return elem_typ.info.func.return_type
+			} else {
+				c.error('cannot call the element of the array, it is not a function',
+					node.pos)
 			}
 		} else if sym.kind == .map {
 			info := sym.info as ast.Map
 			value_typ := c.table.get_type_symbol(info.value_type)
 			if value_typ.info is ast.FnType {
 				return value_typ.info.func.return_type
+			} else {
+				c.error('cannot call the value of the map, it is not a function', node.pos)
 			}
 		} else if sym.kind == .array_fixed {
 			info := sym.info as ast.ArrayFixed
 			elem_typ := c.table.get_type_symbol(info.elem_type)
 			if elem_typ.info is ast.FnType {
 				return elem_typ.info.func.return_type
+			} else {
+				c.error('cannot call the element of the array, it is not a function',
+					node.pos)
 			}
+		} else {
+			// TODO: assert? is this possible?
 		}
 		found = true
 		return ast.string_type

vlib/v/checker/tests/index_invalid_call.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/index_invalid_call.vv:4:20: error: cannot call the value of the map, it is not a function
+    2 | fn main() {
+    3 |     m := map[string]string
+    4 |     eprintln(m['abc']())
+      |                       ^
+    5 |     array := ["", "1"]
+    6 |     array[0]()
+vlib/v/checker/tests/index_invalid_call.vv:6:11: error: cannot call the element of the array, it is not a function
+    4 |     eprintln(m['abc']())
+    5 |     array := ["", "1"]
+    6 |     array[0]()
+      |              ^
+    7 | }

vlib/v/checker/tests/index_invalid_call.vv

@@ -0,0 +1,7 @@
+// fixes https://github.com/vlang/v/issues/11539 , copied example map test code from https://github.com/spytheman
+fn main() {
+	m := map[string]string
+	eprintln(m['abc']())
+	array := ["", "1"]
+	array[0]()
+}