check JS fns/structs too

vlib/v/checker/fn.v

@@ -13,8 +13,9 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			eprintln('>>> post processing node.name: ${node.name:-30} | ${node.generic_names} <=> ${c.table.cur_concrete_types}')
 		}
 	}
-	if node.language == .c && node.generic_names.len > 0 {
-		c.error('C functions cannot be declared as generic', node.pos)
+	if node.language in [.c, .js] && node.generic_names.len > 0 {
+		lang := if node.language == .c { 'C' } else { 'JS' }
+		c.error('${lang} functions cannot be declared as generic', node.pos)
 	}
 	// record the veb route methods (public non-generic methods):
 	if node.generic_names.len > 0 && node.is_pub {

vlib/v/checker/struct.v

@@ -11,8 +11,9 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 	defer {
 		util.timing_measure_cumulative(@METHOD)
 	}
-	if node.language == .c && node.generic_types.len > 0 {
-		c.error('C structs cannot be declared as generic', node.pos)
+	if node.language in [.c, .js] && node.generic_types.len > 0 {
+		lang := if node.language == .c { 'C' } else { 'JS' }
+		c.error('${lang} structs cannot be declared as generic', node.pos)
 	}
 	node_name := if node.scoped_name != '' { node.scoped_name } else { node.name }
 	mut struct_sym, struct_typ_idx := c.table.find_sym_and_type_idx(node_name)

vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.out

@@ -0,0 +1,26 @@
+vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:1:1: error: C structs cannot be declared as generic
+    1 | struct C.Ptr[T] {
+      | ~~~~~~~~~~~~
+    2 |     ptr &T
+    3 | }
+vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:5:1: error: C functions cannot be declared as generic
+    3 | }
+    4 | 
+    5 | fn C.alloc[T]() &T
+      | ~~~~~~~~~~~~~~~~~~
+    6 | 
+    7 | fn JS.encode[T](data string) T
+vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:7:1: error: JS functions cannot be declared as generic
+    5 | fn C.alloc[T]() &T
+    6 | 
+    7 | fn JS.encode[T](data string) T
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    8 | 
+    9 | struct JS.Some[T] {
+vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv:9:1: error: JS structs cannot be declared as generic
+    7 | fn JS.encode[T](data string) T
+    8 | 
+    9 | struct JS.Some[T] {
+      | ~~~~~~~~~~~~~~
+   10 |     i T
+   11 | }

vlib/v/checker/tests/c_struct_and_fn_as_generics_error.vv → vlib/v/checker/tests/c_js_struct_and_fn_as_generics_error.vv

@@ -4,4 +4,10 @@ struct C.Ptr[T] {
 
 fn C.alloc[T]() &T
 
+fn JS.encode[T](data string) T
+
+struct JS.Some[T] {
+	i T
+}
+
 fn main() {}