From e2eddfc0c217c2fc84c5f43bd55c73e2971df699 Mon Sep 17 00:00:00 2001
From: Lewis Russell <lewis6991@gmail.com>
Date: Fri, 30 Jan 2026 13:56:13 +0000
Subject: [PATCH] fix(flow): narrow to assigned function signatures

treat signature targets as compatible when source is function-typed
---
 .../src/compilation/test/flow.rs              | 21 +++++++++++++++++++
 .../semantic/infer/narrow/narrow_type/mod.rs  |  7 +++++++
 2 files changed, 28 insertions(+)

diff --git a/crates/emmylua_code_analysis/src/compilation/test/flow.rs b/crates/emmylua_code_analysis/src/compilation/test/flow.rs
index a5f068d79..336a44413 100644
--- a/crates/emmylua_code_analysis/src/compilation/test/flow.rs
+++ b/crates/emmylua_code_analysis/src/compilation/test/flow.rs
@@ -258,6 +258,27 @@ print(a.field)
         ));
     }
 
+    #[test]
+    fn test_doc_function_assignment_narrowing() {
+        let mut ws = VirtualWorkspace::new();
+
+        let code = r#"
+        local i --- @type integer|fun():string
+        i = function() end
+        _ = i()
+        A = i
+        "#;
+
+        ws.def(code);
+
+        assert!(ws.check_code_for(DiagnosticCode::CallNonCallable, code));
+        assert!(ws.check_code_for(DiagnosticCode::NeedCheckNil, code));
+
+        let a = ws.expr_ty("A");
+        let a_desc = ws.humanize_type_detailed(a);
+        assert_eq!(a_desc, "fun()");
+    }
+
     #[test]
     fn test_issue_224() {
         let mut ws = VirtualWorkspace::new();
diff --git a/crates/emmylua_code_analysis/src/semantic/infer/narrow/narrow_type/mod.rs b/crates/emmylua_code_analysis/src/semantic/infer/narrow/narrow_type/mod.rs
index 15a719325..88872141a 100644
--- a/crates/emmylua_code_analysis/src/semantic/infer/narrow/narrow_type/mod.rs
+++ b/crates/emmylua_code_analysis/src/semantic/infer/narrow/narrow_type/mod.rs
@@ -4,6 +4,7 @@ use crate::{DbIndex, LuaType, TypeOps, get_real_type, semantic::type_check::is_s
 pub use false_or_nil_type::{narrow_false_or_nil, remove_false_or_nil};
 
 // need to be optimized
+// `source` is the current/antecedent type, `target` is the narrowing candidate (e.g. assignment RHS).
 pub fn narrow_down_type(db: &DbIndex, source: LuaType, target: LuaType) -> Option<LuaType> {
     if source == target {
         return Some(source);
@@ -73,6 +74,12 @@ pub fn narrow_down_type(db: &DbIndex, source: LuaType, target: LuaType) -> Optio
                 return Some(source);
             }
         }
+        LuaType::Signature(_) => {
+            if real_source_ref.is_function() {
+                // Prefer the assigned closure signature, even when the antecedent is a doc function.
+                return Some(target.clone());
+            }
+        }
         LuaType::Thread => {
             if real_source_ref.is_thread() {
                 return Some(source);