checker: check generic interface declaration (#15108)

vlib/v/checker/interface.v

@@ -40,6 +40,18 @@ pub fn (mut c Checker) interface_decl(mut node ast.InterfaceDecl) {
 						embed.pos)
 					continue
 				}
+				// Ensure each generic type of the embed was declared in the interface's definition
+				if node.generic_types.len > 0 && embed.typ.has_flag(.generic) {
+					embed_generic_names := c.table.generic_type_names(embed.typ)
+					node_generic_names := node.generic_types.map(c.table.type_to_str(it))
+					for name in embed_generic_names {
+						if name !in node_generic_names {
+							interface_generic_names := node_generic_names.join(', ')
+							c.error('generic type name `$name` is not mentioned in interface `$node.name<$interface_generic_names>`',
+								embed.pos)
+						}
+					}
+				}
 				isym_info := isym.info as ast.Interface
 				for f in isym_info.fields {
 					if !efnames_ds_info[f.name] {
@@ -115,6 +127,18 @@ pub fn (mut c Checker) interface_decl(mut node ast.InterfaceDecl) {
 			}
 			if method.return_type.has_flag(.generic) {
 				has_generic_types = true
+				// Ensure each generic type of the method was declared in the interface's definition
+				if node.generic_types.len > 0 {
+					method_generic_names := c.table.generic_type_names(method.return_type)
+					node_generic_names := node.generic_types.map(c.table.type_to_str(it))
+					for name in method_generic_names {
+						if name !in node_generic_names {
+							interface_generic_names := node_generic_names.join(', ')
+							c.error('generic type name `$name` is not mentioned in interface `$node.name<$interface_generic_names>`',
+								method.return_type_pos)
+						}
+					}
+				}
 			}
 			for j, param in method.params {
 				if j == 0 && is_js {
@@ -128,6 +152,18 @@ pub fn (mut c Checker) interface_decl(mut node ast.InterfaceDecl) {
 					c.error('invalid use of reserved type `$param.name` as a parameter name',
 						param.pos)
 				}
+				// Ensure each generic type of the method was declared in the interface's definition
+				if node.generic_types.len > 0 && param.typ.has_flag(.generic) {
+					method_generic_names := c.table.generic_type_names(param.typ)
+					node_generic_names := node.generic_types.map(c.table.type_to_str(it))
+					for name in method_generic_names {
+						if name !in node_generic_names {
+							interface_generic_names := node_generic_names.join(', ')
+							c.error('generic type name `$name` is not mentioned in interface `$node.name<$interface_generic_names>`',
+								param.type_pos)
+						}
+					}
+				}
 				if is_js {
 					ptyp := c.table.sym(param.typ)
 					if !ptyp.is_js_compatible() && !(j == method.params.len - 1

vlib/v/checker/tests/generics_interface_decl_no_mention_err.out

@@ -0,0 +1,21 @@
+vlib/v/checker/tests/generics_interface_decl_no_mention_err.vv:4:2: error: generic type name `T` is not mentioned in interface `Foo<U>`
+    2 |
+    3 | interface Foo<U> {
+    4 |     Bar<T>
+      |     ~~~
+    5 |     foo(u U, p P)
+    6 |     bar(u U) []P
+vlib/v/checker/tests/generics_interface_decl_no_mention_err.vv:5:13: error: generic type name `P` is not mentioned in interface `Foo<U>`
+    3 | interface Foo<U> {
+    4 |     Bar<T>
+    5 |     foo(u U, p P)
+      |                ^
+    6 |     bar(u U) []P
+    7 | }
+vlib/v/checker/tests/generics_interface_decl_no_mention_err.vv:6:11: error: generic type name `P` is not mentioned in interface `Foo<U>`
+    4 |     Bar<T>
+    5 |     foo(u U, p P)
+    6 |     bar(u U) []P
+      |              ~~~
+    7 | }
+    8 |

vlib/v/checker/tests/generics_interface_decl_no_mention_err.vv

@@ -0,0 +1,10 @@
+fn main() {}
+
+interface Foo<U> {
+	Bar<T>
+	foo(u U, p P)
+	bar(u U) []P
+}
+
+interface Bar<T> {
+}