fix flow: self 删除 nil

Author: xuhuanzy

crates/emmylua_code_analysis/src/compilation/test/flow.rs

@@ -1258,4 +1258,30 @@ end
             "#,
         ));
     }
+
+    #[test]
+    fn test_self_1() {
+        let mut ws = VirtualWorkspace::new();
+        ws.def(
+            r#"
+            ---@class Node
+            ---@field parent? Node 
+
+            ---@class Subject<T>: Node
+            ---@field package root? Node 
+            Subject = {}
+            "#,
+        );
+        ws.def(
+            r#"
+            function Subject:add()
+                if self == self.parent then
+                    A = self
+                end
+            end
+            "#,
+        );
+        let a = ws.expr_ty("A");
+        assert_eq!(ws.humanize_type(a), "Node");
+    }
 }

crates/emmylua_code_analysis/src/semantic/infer/narrow/condition_flow/binary_flow.rs

@@ -237,8 +237,16 @@ fn maybe_var_eq_narrow(
             }
 
             let right_expr_type = infer_expr(db, cache, right_expr)?;
+
             let result_type = match condition_flow {
-                InferConditionFlow::TrueCondition => right_expr_type,
+                InferConditionFlow::TrueCondition => {
+                    // self 是特殊的, 我们删除其 nil 类型
+                    if var_ref_id.is_self_ref() && !right_expr_type.is_nil() {
+                        TypeOps::Remove.apply(db, &right_expr_type, &LuaType::Nil)
+                    } else {
+                        right_expr_type
+                    }
+                }
                 InferConditionFlow::FalseCondition => {
                     let antecedent_flow_id = get_single_antecedent(tree, flow_node)?;
                     let antecedent_type =

crates/emmylua_code_analysis/src/semantic/infer/narrow/var_ref_id.rs

@@ -61,6 +61,13 @@ impl VarRefId {
             }
         }
     }
+
+    pub fn is_self_ref(&self) -> bool {
+        match self {
+            VarRefId::SelfRef(_) => true,
+            _ => false,
+        }
+    }
 }
 
 fn get_call_expr_var_ref_id(