From f5e03deaa80270cb86fe053265173e0752c4ee26 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 23 Mar 2025 13:40:27 -0300
Subject: [PATCH] checker: fix chan element type validation with inexistent
 type (fix #23978) (#24008)

---
 vlib/v/ast/table.v                        | 10 +++++++---
 vlib/v/checker/checker.v                  | 10 ++++++++++
 vlib/v/checker/tests/chan_unknown_err.out |  7 +++++++
 vlib/v/checker/tests/chan_unknown_err.vv  |  8 ++++++++
 4 files changed, 32 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/checker/tests/chan_unknown_err.out
 create mode 100644 vlib/v/checker/tests/chan_unknown_err.vv

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index f453c8b03..ce9fa1cfb 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -1499,9 +1499,13 @@ pub fn (t &Table) known_type_names() []string {
 	for _, idx in t.type_idxs {
 		typ := idx_to_type(idx)
 		// Skip `int_literal_type_idx` and `float_literal_type_idx` because they shouldn't be visible to the User.
-		if idx !in [0, int_literal_type_idx, float_literal_type_idx] && t.known_type_idx(typ)
-			&& t.sym(typ).kind != .function {
-			res << t.type_to_str(typ)
+		if idx !in [0, int_literal_type_idx, float_literal_type_idx] && t.known_type_idx(typ) {
+			tsym := t.sym(typ)
+			if tsym.kind !in [.function, .chan] {
+				res << t.type_to_str(typ)
+			} else if tsym.info is Chan && t.sym(tsym.info.elem_type).kind != .placeholder {
+				res << t.type_to_str(tsym.info.elem_type)
+			}
 		}
 	}
 	return res
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 1a6a26ae0..488821c7f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -5487,6 +5487,16 @@ fn (mut c Checker) ensure_type_exists(typ ast.Type, pos token.Pos) bool {
 				}
 			}
 		}
+		.chan {
+			if sym.info is ast.Chan {
+				if !c.ensure_type_exists((sym.info as ast.Chan).elem_type, token.Pos{
+					...pos
+					col: pos.col + 5
+				}) {
+					return false
+				}
+			}
+		}
 		else {}
 	}
 	return true
diff --git a/vlib/v/checker/tests/chan_unknown_err.out b/vlib/v/checker/tests/chan_unknown_err.out
new file mode 100644
index 000000000..e9bbdd337
--- /dev/null
+++ b/vlib/v/checker/tests/chan_unknown_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/chan_unknown_err.vv:7:11: error: unknown type `DoesNotExist`.
+Did you mean `DoesNotExists`?
+    5 | struct ChanBug {
+    6 | pub mut:
+    7 |     bug chan DoesNotExist
+      |              ~~~~~~~~~~~~
+    8 | }
diff --git a/vlib/v/checker/tests/chan_unknown_err.vv b/vlib/v/checker/tests/chan_unknown_err.vv
new file mode 100644
index 000000000..60d45325c
--- /dev/null
+++ b/vlib/v/checker/tests/chan_unknown_err.vv
@@ -0,0 +1,8 @@
+module main
+
+struct DoesNotExists {}
+
+struct ChanBug {
+pub mut:
+	bug chan DoesNotExist
+}
-- 
2.39.5