From eee9ee52006ae004c2224533b4fc208ad403bb2d Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Tue, 12 Nov 2024 16:33:51 +0530
Subject: [PATCH] checker: disallow `foo[T]` as a value  (#22820)

---
 vlib/v/checker/checker.v                      | 11 ++++++++++
 ...generic_fn_generic_name_unresolved_err.out | 21 +++++++++++++++++++
 .../generic_fn_generic_name_unresolved_err.vv | 15 +++++++++++++
 3 files changed, 47 insertions(+)
 create mode 100644 vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.out
 create mode 100644 vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 9e778a83b..c9a22a27d 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -4009,6 +4009,17 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 					c.error('`${node.name}` is a generic fn, you should pass its concrete types, e.g. ${node.name}[int]',
 						node.pos)
 				}
+				mut has_generic := false // foo[T] instead of foo[int]
+				for concrete_type in node.concrete_types {
+					if concrete_type.has_flag(.generic) {
+						has_generic = true
+					}
+				}
+				if c.table.cur_fn != unsafe { nil } && c.table.cur_concrete_types.len == 0
+					&& has_generic && c.table.sym(c.expected_type).kind != .function {
+					c.error('a generic fn with generic types, cannot be used outside of another generic fn',
+						node.pos)
+				}
 			}
 			return c.resolve_var_fn(func, mut node, name)
 		}
diff --git a/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.out b/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.out
new file mode 100644
index 000000000..4a5f4c1ff
--- /dev/null
+++ b/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.out
@@ -0,0 +1,21 @@
+vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv:8:7: error: a generic fn with generic types, cannot be used outside of another generic fn
+    6 | 
+    7 | fn main() {
+    8 |     _ := func[T]
+      |          ~~~~
+    9 |     _ := {
+   10 |         'test': func[T]
+vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv:10:11: error: a generic fn with generic types, cannot be used outside of another generic fn
+    8 |     _ := func[T]
+    9 |     _ := {
+   10 |         'test': func[T]
+      |                 ~~~~
+   11 |     }
+   12 |     _ := {
+vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv:13:3: error: a generic fn with generic types, cannot be used outside of another generic fn
+   11 |     }
+   12 |     _ := {
+   13 |         func[T]: 'test'
+      |         ~~~~
+   14 |     }
+   15 | }
diff --git a/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv b/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv
new file mode 100644
index 000000000..ad6ed25de
--- /dev/null
+++ b/vlib/v/checker/tests/generic_fn_generic_name_unresolved_err.vv
@@ -0,0 +1,15 @@
+module main
+
+fn func[T](arg string, val T) int {
+	return 2
+}
+
+fn main() {
+	_ := func[T]
+	_ := {
+		'test': func[T]
+	}
+	_ := {
+		func[T]: 'test'
+	}
+}
-- 
2.39.5