From 0b2b06df3c144e02a87ca73813e795454c86ff9f Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Wed, 30 Oct 2024 16:56:52 -0300
Subject: [PATCH] checker: fix missing check for fn var with generic return
 inherited to anon fn (fix #19045) (#22683)

---
 vlib/v/checker/fn.v                           | 16 +++++++++
 .../tests/anon_missing_generic_err.out        | 21 ++++++++++++
 .../checker/tests/anon_missing_generic_err.vv | 33 +++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 vlib/v/checker/tests/anon_missing_generic_err.out
 create mode 100644 vlib/v/checker/tests/anon_missing_generic_err.vv

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 8c5c7d89f..7e5e21db6 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -608,6 +608,22 @@ fn (mut c Checker) anon_fn(mut node ast.AnonFn) ast.Type {
 			c.error('original `${parent_var.name}` is immutable, declare it with `mut` to make it mutable',
 				var.pos)
 		}
+		if parent_var.typ != ast.no_type {
+			parent_var_sym := c.table.final_sym(parent_var.typ)
+			if parent_var_sym.info is ast.FnType {
+				ret_typ := c.unwrap_generic(parent_var_sym.info.func.return_type)
+				if ret_typ.has_flag(.generic) {
+					generic_names := c.table.generic_type_names(ret_typ)
+					curr_list := c.table.cur_fn.generic_names.join(', ')
+					for name in generic_names {
+						if name !in c.table.cur_fn.generic_names {
+							c.error('Add the generic type `${name}` to the anon fn generic list type, that is currently `[${curr_list}]`',
+								var.pos)
+						}
+					}
+				}
+			}
+		}
 		if parent_var.expr is ast.IfGuardExpr {
 			sym := c.table.sym(parent_var.expr.expr_type)
 			if sym.info is ast.MultiReturn {
diff --git a/vlib/v/checker/tests/anon_missing_generic_err.out b/vlib/v/checker/tests/anon_missing_generic_err.out
new file mode 100644
index 000000000..76e88e30e
--- /dev/null
+++ b/vlib/v/checker/tests/anon_missing_generic_err.out
@@ -0,0 +1,21 @@
+vlib/v/checker/tests/anon_missing_generic_err.vv:8:2: notice: uninitialized `fn` struct fields are not allowed, since they can result in segfaults; use `?fn` or `@[required]` or initialize the field with `=` (if you absolutely want to have unsafe function pointers, use `= unsafe { nil }`)
+    6 | 
+    7 | struct Factory {
+    8 |     build fn () !
+      |     ~~~~~~~~~~~~~
+    9 | }
+   10 |
+vlib/v/checker/tests/anon_missing_generic_err.vv:21:14: error: Add the generic type `E` to the anon fn generic list type, that is currently `[F]`
+   19 | fn use_factory[F, E](factory fn (dep F) !E) Factory {
+   20 |     return Factory{
+   21 |         build: fn [factory] [F]() ! {
+      |                    ~~~~~~~
+   22 |             mut dep := F{}
+   23 |             inject[F](mut dep)!
+vlib/v/checker/tests/anon_missing_generic_err.vv:12:16: error: $for expects a type name or variable name to be used here, but F is not a type or variable name
+   10 | 
+   11 | fn inject[T](mut serv T) ! {
+   12 |     $for field in T.fields {
+      |                   ^
+   13 |         if field.typ is string {
+   14 |             serv.$(field.name) = 'Hello world!'
diff --git a/vlib/v/checker/tests/anon_missing_generic_err.vv b/vlib/v/checker/tests/anon_missing_generic_err.vv
new file mode 100644
index 000000000..0ba34f24e
--- /dev/null
+++ b/vlib/v/checker/tests/anon_missing_generic_err.vv
@@ -0,0 +1,33 @@
+struct Test {
+	something string
+}
+
+struct Dependency {}
+
+struct Factory {
+	build fn () !
+}
+
+fn inject[T](mut serv T) ! {
+	$for field in T.fields {
+		if field.typ is string {
+			serv.$(field.name) = 'Hello world!'
+		}
+	}
+}
+
+fn use_factory[F, E](factory fn (dep F) !E) Factory {
+	return Factory{
+		build: fn [factory] [F]() ! {
+			mut dep := F{}
+			inject[F](mut dep)!
+			dump(factory(dep)!)
+		}
+	}
+}
+
+use_factory[Dependency, Test](fn (dep Dependency) !Test {
+	return Test{
+		something: 'daleks!'
+	}
+}).build()!
-- 
2.39.5