disallow C functions and structs to be declared as generic

vlib/v/checker/fn.v

@@ -13,6 +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)
+	}
 	// record the veb route methods (public non-generic methods):
 	if node.generic_names.len > 0 && node.is_pub {
 		typ_vweb_result := c.table.find_type_idx('veb.Result')

vlib/v/checker/struct.v

@@ -11,6 +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)
+	}
 	mut struct_sym, struct_typ_idx := c.table.find_sym_and_type_idx(node.name)
 	mut has_generic_types := false
 	if mut struct_sym.info is ast.Struct {

vlib/v/checker/tests/c_struct_and_fn_as_generics_error.out

@@ -0,0 +1,12 @@
+vlib/v/checker/tests/c_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_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 main() {}

vlib/v/checker/tests/c_struct_and_fn_as_generics_error.vv

@@ -0,0 +1,7 @@
+struct C.Ptr[T] {
+	ptr &T
+}
+
+fn C.alloc[T]() &T
+
+fn main() {}