fix #25794, infer parameter type from default value

pkg/analyzer/test/src/task/strong/inferred_type_test.dart

Index: pkg/analyzer/test/src/task/strong/inferred_type_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
index ccb9587d19588269d260d14d20633fd42bca4fba..3674d99ca25e4b8a474af8e74b15bba419f1dd11 100644
--- a/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
+++ b/pkg/analyzer/test/src/task/strong/inferred_type_test.dart
@@ -1913,6 +1913,33 @@ foo() {
 ''');
   }
 
+  void test_inferDefaultFormalParameter() {
+    var unit = checkFile('''
+f([x = 42]) {}
+g({x: 'hi'}) {}
+''');
+    expect(unit.functions[0].parameters[0].type.toString(), 'int');
+    expect(unit.functions[1].parameters[0].type.toString(), 'String');
+  }
+
+  void test_inferDefaultFormalParameter_fieldFormal() {
+    checkFile('''
+class C {
+  int x;
+  var y;
+  C({this.x: /*error:INVALID_ASSIGNMENT*/0.0, this.y: 'hi'}) {
+    String z = /*info:DYNAMIC_CAST*/y;
+  }
+  C.c([this.x =/*error:INVALID_ASSIGNMENT*/0.0, this.y = 'hi']) {
+    String z = /*info:DYNAMIC_CAST*/y;
+  }
+  m() {
+    String z = /*info:DYNAMIC_CAST*/y;
+  }
+}
+''');
+  }
+
   void test_inferedType_usesSyntheticFunctionType() {
     var mainUnit = checkFile('''
 int f() => null;