fix infer generic

Author: xuhuanzy

crates/emmylua_code_analysis/src/semantic/generic/instantiate_type/instantiate_func_generic.rs

@@ -72,11 +72,11 @@ pub fn instantiate_func_generic(
     if !generic_tpls.is_empty() {
         context.substitutor.add_need_infer_tpls(generic_tpls);
 
-        // 判断是否指定了泛型
         if let Some(type_list) = call_expr.get_call_generic_type_list() {
+            // 如果使用了`obj:abc--[[@<string>]]("abc")`强制指定了泛型, 那么我们只需要直接应用
             apply_call_generic_type_list(db, file_id, &mut context, &type_list);
         } else {
-            // 没有指定泛型, 从调用参数中推断
+            // 如果没有指定泛型, 则需要从调用参数中推断
             infer_generic_types_from_call(
                 db,
                 &mut context,
@@ -155,12 +155,16 @@ fn infer_generic_types_from_call(
         if !func_param_type.is_variadic()
             && check_expr_can_later_infer(context, func_param_type, call_arg_expr)?
         {
-            // If the argument cannot be inferred later, we will handle it later.
+            // 如果参数不能被后续推断, 那么我们先不处理
             unresolve_tpls.push((func_param_type.clone(), call_arg_expr.clone()));
             continue;
         }
 
-        let arg_type = infer_expr(db, context.cache, call_arg_expr.clone())?;
+        let arg_type = match infer_expr(db, context.cache, call_arg_expr.clone()) {
+            Ok(t) => t,
+            Err(InferFailReason::FieldNotFound) => LuaType::Nil, // 对于未找到的字段, 我们认为是 nil 以执行后续推断
+            Err(e) => return Err(e),
+        };
         match (func_param_type, &arg_type) {
             (LuaType::Variadic(variadic), _) => {
                 let mut arg_types = vec![];

crates/emmylua_ls/src/handlers/test/completion_test.rs

@@ -2339,4 +2339,38 @@ mod tests {
 
         Ok(())
     }
+
+    #[gtest]
+    fn test_function_generic_value_is_nil() -> Result<()> {
+        let mut ws = ProviderVirtualWorkspace::new();
+        ws.def(
+            r#"
+            ---@class Expect
+            ---@overload fun<T>(actual: T): Assertion<T>
+
+            ---@class Assertion<T>
+            ---@field toBe fun(self: self)
+
+            ---@type table
+            GTable = {}
+            "#,
+        );
+
+        check!(ws.check_completion_with_kind(
+            r#"
+            ---@type Expect
+            local expect = {}
+
+            expect(GTable["a"]):<??>
+            "#,
+            vec![VirtualCompletionItem {
+                label: "toBe".to_string(),
+                kind: CompletionItemKind::FUNCTION,
+                label_detail: Some("()".to_string()),
+            },],
+            CompletionTriggerKind::TRIGGER_CHARACTER
+        ));
+
+        Ok(())
+    }
 }