fix #844

Author: xuhuanzy

crates/emmylua_code_analysis/src/diagnostic/test/param_type_check_test.rs

@@ -1355,4 +1355,29 @@ mod test {
         "#,
         ));
     }
+
+    #[test]
+    fn test_fix_issue_844() {
+        let mut ws = VirtualWorkspace::new();
+        ws.def(
+            r#"
+        ---@alias Tester fun(customTesters: Tester[]): boolean?
+
+        ---@generic V
+        ---@param t V[]
+        ---@return fun(tbl: any):int, V
+        function ipairs(t) end
+        "#,
+        );
+        assert!(ws.check_code_for(
+            DiagnosticCode::ParamTypeMismatch,
+            r#"
+            ---@param newTesters Tester[]
+            local function addMatchers(newTesters)
+                for _, tester in ipairs(newTesters) do
+                end
+            end
+        "#
+        ));
+    }
 }

crates/emmylua_code_analysis/src/semantic/type_check/complex_type/array_type_check.rs

@@ -13,7 +13,11 @@ pub fn check_array_type_compact(
     compact_type: &LuaType,
     check_guard: TypeCheckGuard,
 ) -> TypeCheckResult {
-    let source_base = TypeOps::Union.apply(context.db, source_base, &LuaType::Nil);
+    let source_base = if context.db.get_emmyrc().strict.array_index {
+        TypeOps::Union.apply(context.db, source_base, &LuaType::Nil)
+    } else {
+        source_base.clone()
+    };
 
     match compact_type {
         LuaType::Array(compact_array_type) => {

crates/emmylua_code_analysis/src/semantic/type_check/mod.rs

@@ -9,6 +9,8 @@ mod type_check_context;
 mod type_check_fail_reason;
 mod type_check_guard;
 
+use std::ops::Deref;
+
 use complex_type::check_complex_type_compact;
 use func_type::{check_doc_func_type_compact, check_sig_type_compact};
 use generic_type::check_generic_type_compact;
@@ -18,6 +20,7 @@ pub use type_check_fail_reason::TypeCheckFailReason;
 use type_check_guard::TypeCheckGuard;
 
 use crate::{
+    LuaUnionType,
     db_index::{DbIndex, LuaType},
     semantic::type_check::type_check_context::TypeCheckContext,
 };
@@ -198,6 +201,12 @@ fn fast_eq_check(a: &LuaType, b: &LuaType) -> bool {
         | (LuaType::Unknown, LuaType::Unknown)
         | (LuaType::Any, LuaType::Any) => true,
         (LuaType::Ref(type_id_left), LuaType::Ref(type_id_right)) => type_id_left == type_id_right,
+        (LuaType::Union(u), LuaType::Ref(type_id_right)) => {
+            if let LuaUnionType::Nullable(LuaType::Ref(type_id_left)) = u.deref() {
+                return type_id_left == type_id_right;
+            }
+            false
+        }
         _ => false,
     }
 }