From 37f94e44109ca5cea4934ff4a15d0e8b24025266 Mon Sep 17 00:00:00 2001
From: phanium <91544758+phanen@users.noreply.github.com>
Date: Sat, 27 Dec 2025 10:58:15 +0800
Subject: [PATCH] fix(diagnostics): compare non-nil with nil

---
 .../test/unnecessary_assert_test.rs           | 17 +++++++++++++++
 .../diagnostic/test/unnecessary_if_test.rs    | 21 +++++++++++++++++++
 .../src/semantic/infer/infer_binary/mod.rs    | 10 +++++++++
 3 files changed, 48 insertions(+)

diff --git a/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_assert_test.rs b/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_assert_test.rs
index 1706d87e3..e7ee8e7e8 100644
--- a/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_assert_test.rs
+++ b/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_assert_test.rs
@@ -127,4 +127,21 @@ mod test {
             "#
         ));
     }
+
+    #[test]
+    fn test_nonnli_with_nil() {
+        let mut ws = VirtualWorkspace::new();
+        assert!(!ws.check_code_for(
+            DiagnosticCode::UnnecessaryAssert,
+            r#"
+            assert("abc" ~= nil)
+            "#
+        ));
+        assert!(!ws.check_code_for(
+            DiagnosticCode::UnnecessaryAssert,
+            r#"
+            assert(1 == nil)
+            "#
+        ));
+    }
 }
diff --git a/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_if_test.rs b/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_if_test.rs
index e16a652bb..f027e2ebb 100644
--- a/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_if_test.rs
+++ b/crates/emmylua_code_analysis/src/diagnostic/test/unnecessary_if_test.rs
@@ -26,4 +26,25 @@ mod test {
         "#
         ));
     }
+
+    #[test]
+    fn test_nonnil_with_nil() {
+        let mut ws = VirtualWorkspace::new();
+        assert!(!ws.check_code_for(
+            DiagnosticCode::UnnecessaryIf,
+            r#"
+            if 1 ~= nil then
+                error("Impossible")
+            end
+            "#
+        ));
+        assert!(!ws.check_code_for(
+            DiagnosticCode::UnnecessaryIf,
+            r#"
+            if "abc" == nil then
+                error("Impossible")
+            end
+            "#
+        ));
+    }
 }
diff --git a/crates/emmylua_code_analysis/src/semantic/infer/infer_binary/mod.rs b/crates/emmylua_code_analysis/src/semantic/infer/infer_binary/mod.rs
index 7b033d03a..cbe0f63f3 100644
--- a/crates/emmylua_code_analysis/src/semantic/infer/infer_binary/mod.rs
+++ b/crates/emmylua_code_analysis/src/semantic/infer/infer_binary/mod.rs
@@ -506,6 +506,16 @@ fn infer_cmp_expr(_: &DbIndex, left: LuaType, right: LuaType, op: BinaryOperator
             BinaryOperator::OpNe => Ok(LuaType::BooleanConst(i != j)),
             _ => Ok(LuaType::Boolean),
         },
+        (LuaType::Nil, right) if right.is_const() => match op {
+            BinaryOperator::OpEq => Ok(LuaType::BooleanConst(false)),
+            BinaryOperator::OpNe => Ok(LuaType::BooleanConst(true)),
+            _ => Ok(LuaType::Boolean),
+        },
+        (left, LuaType::Nil) if left.is_const() => match op {
+            BinaryOperator::OpEq => Ok(LuaType::BooleanConst(false)),
+            BinaryOperator::OpNe => Ok(LuaType::BooleanConst(true)),
+            _ => Ok(LuaType::Boolean),
+        },
         (left, right) if left.is_const() && right.is_const() => Ok(LuaType::BooleanConst(false)),
         _ => Ok(LuaType::Boolean),
     }