parser: ensure generic function declaration specifies type names (fix #9959) (#9967)

vlib/v/checker/checker.v

@@ -6752,6 +6752,24 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 		c.file.generic_fns << node
 		return
 	}
+	// Check generics fn/method without generic type parameters
+	mut need_generic_names := false
+	if node.generic_names.len == 0 {
+		if node.return_type.has_flag(.generic) {
+			need_generic_names = true
+		} else {
+			for param in node.params {
+				if param.typ.has_flag(.generic) {
+					need_generic_names = true
+					break
+				}
+			}
+		}
+		if need_generic_names {
+			c.error('generic function declaration must specify generic type names, e.g. foo<T>',
+				node.pos)
+		}
+	}
 	if node.language == .v && !c.is_builtin_mod {
 		c.check_valid_snake_case(node.name, 'function name', node.pos)
 	}

vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:26:1: error: generic function declaration must specify generic type names, e.g. foo<T>
+   24 | }
+   25 |
+   26 | fn g_worker(g Generic<T>) {
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~
+   27 |     t := <-g.ch
+   28 |     handle(t)
+vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv:32:1: error: generic function declaration must specify generic type names, e.g. foo<T>
+   30 | }
+   31 |
+   32 | fn handle(t T) {
+      | ~~~~~~~~~~~~~~
+   33 |     println("hi")
+   34 | }

vlib/v/checker/tests/generic_fn_decl_without_generic_names_err.vv

@@ -0,0 +1,34 @@
+struct Generic<T> {
+	ch chan T
+}
+
+struct Concrete {
+	msg string
+}
+
+fn main() {
+	g := create_generic_t<Concrete>()
+	g.ch <- Concrete{
+		msg: 'hello'
+	}
+}
+
+fn create_generic_t<T>() Generic<T> {
+	g := Generic{
+		ch: chan T{}
+	}
+
+	go g_worker(g)
+
+	return g
+}
+
+fn g_worker(g Generic<T>) {
+	t := <-g.ch
+	handle(t)
+	// println("${t.msg}")
+}
+
+fn handle(t T) {
+	println("hi")
+}

vlib/v/checker/tests/receiver_unknown_type_single_letter.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/receiver_unknown_type_single_letter.vv:1:5: error: unknown type `A`
-    1 | fn (p A) foo() {}
-      |     ~~~
+vlib/v/checker/tests/receiver_unknown_type_single_letter.vv:1:1: error: unknown type `Abc`
+    1 | fn (p Abc) foo() {}
+      | ~~~~~~~~~~~~~~~~
     2 |

vlib/v/checker/tests/receiver_unknown_type_single_letter.vv

@@ -1,2 +1,2 @@
-fn (p A) foo() {}
+fn (p Abc) foo() {}
 

vlib/v/parser/fn.v

@@ -336,6 +336,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	short_fn_name := name
 	is_main := short_fn_name == 'main' && p.mod == 'main'
 	is_test := short_fn_name.starts_with('test_') || short_fn_name.starts_with('testsuite_')
+
 	// Register
 	if is_method {
 		mut type_sym := p.table.get_type_symbol(rec.typ)