fix some semantic for safe nav

Author: CppCXY

crates/emmylua_code_analysis/src/diagnostic/checker/need_check_nil.rs

@@ -58,6 +58,10 @@ fn check_index_expr(
     semantic_model: &SemanticModel,
     index_expr: LuaIndexExpr,
 ) -> Option<()> {
+    if index_expr.is_safe_index() {
+        return None;
+    }
+
     let prefix = index_expr.get_prefix_expr()?;
     let prefix_type = semantic_model.infer_expr(prefix.clone()).ok()?;
     if prefix_type.is_nullable() {

crates/emmylua_code_analysis/src/semantic/infer/infer_index/mod.rs

@@ -88,17 +88,17 @@ pub fn infer_index_expr(
         &InferGuard::new(),
     )?;
 
-    let result_type = if is_safe && prefix_type.is_nullable() {
-        TypeOps::Union.apply(db, &member_type, &LuaType::Nil)
+    let mut result_type = if pass_flow {
+        infer_member_type_pass_flow(db, cache, index_expr, member_type)?
     } else {
         member_type
     };
 
-    if pass_flow {
-        infer_member_type_pass_flow(db, cache, index_expr, result_type)
-    } else {
-        Ok(result_type)
+    if is_safe && prefix_type.is_optional() {
+        result_type = TypeOps::Union.apply(db, &result_type, &LuaType::Nil);
     }
+
+    Ok(result_type)
 }
 
 pub fn infer_ternary_expr(

crates/emmylua_code_analysis/src/semantic/infer/test.rs

@@ -228,4 +228,20 @@ mod test {
 
         assert_eq!(ws.expr_ty("c"), ws.ty("any"));
     }
+
+    #[test]
+    fn test_safe_nav() {
+        let mut ws = VirtualWorkspace::new();
+        ws.def(
+            r#"
+        --- @class MyClass
+        --- @field public myField? string
+        local MyClass = {}
+
+        a = MyClass.myField?.byte
+        "#,
+        );
+
+        assert!(ws.expr_ty("a").is_nullable());
+    }
 }