[cfe] Update message for missing default value

Update in response to issue #44329 and to match the change
in https://dart-review.googlesource.com/c/sdk/+/174300

Change-Id: Ia28887f0fad54927b82b7aa29acb88231053cd6a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/174800
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

Author: johnniwinther

pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart

@@ -3936,7 +3936,9 @@ const Template<
             Message Function(
                 String name, DartType _type, bool isNonNullableByDefault)>(
         messageTemplate:
-            r"""Optional parameter '#name' should have a default value because its type '#type' doesn't allow null.""",
+            r"""The parameter '#name' can't have a value of 'null' because of its type '#type', but the implicit default value is 'null'.""",
+        tipTemplate:
+            r"""Try adding either an explicit non-'null' default value or the 'required' modifier.""",
         withArguments:
             _withArgumentsOptionalNonNullableWithoutInitializerError);
 
@@ -3945,11 +3947,11 @@ const Code<
         Message Function(
             String name, DartType _type, bool isNonNullableByDefault)>
     codeOptionalNonNullableWithoutInitializerError = const Code<
-        Message Function(
-            String name, DartType _type, bool isNonNullableByDefault)>(
-  "OptionalNonNullableWithoutInitializerError",
-  templateOptionalNonNullableWithoutInitializerError,
-);
+            Message Function(
+                String name, DartType _type, bool isNonNullableByDefault)>(
+        "OptionalNonNullableWithoutInitializerError",
+        templateOptionalNonNullableWithoutInitializerError,
+        analyzerCodes: <String>["MISSING_DEFAULT_VALUE_FOR_PARAMETER"]);
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 Message _withArgumentsOptionalNonNullableWithoutInitializerError(
@@ -3961,8 +3963,9 @@ Message _withArgumentsOptionalNonNullableWithoutInitializerError(
   String type = typeParts.join();
   return new Message(codeOptionalNonNullableWithoutInitializerError,
       message:
-          """Optional parameter '${name}' should have a default value because its type '${type}' doesn't allow null.""" +
+          """The parameter '${name}' can't have a value of 'null' because of its type '${type}', but the implicit default value is 'null'.""" +
               labeler.originMessages,
+      tip: """Try adding either an explicit non-'null' default value or the 'required' modifier.""",
       arguments: {'name': name, 'type': _type});
 }
 

pkg/front_end/messages.status

@@ -629,8 +629,6 @@ OperatorParameterMismatch1/example: Fail
 OperatorParameterMismatch2/example: Fail
 OperatorWithOptionalFormals/analyzerCode: Fail
 OperatorWithOptionalFormals/example: Fail
-OptionalNonNullableWithoutInitializerError/analyzerCode: Fail
-OptionalNonNullableWithoutInitializerWarning/analyzerCode: Fail
 OverrideFewerNamedArguments/example: Fail
 OverrideFewerPositionalArguments/example: Fail
 OverrideMismatchNamedParameter/example: Fail

pkg/front_end/messages.yaml

@@ -4585,7 +4585,9 @@ ValueForRequiredParameterNotProvidedError:
   template: "Required named parameter '#name' must be provided."
 
 OptionalNonNullableWithoutInitializerError:
-  template: "Optional parameter '#name' should have a default value because its type '#type' doesn't allow null."
+  template: "The parameter '#name' can't have a value of 'null' because of its type '#type', but the implicit default value is 'null'."
+  tip: "Try adding either an explicit non-'null' default value or the 'required' modifier."
+  analyzerCode: MISSING_DEFAULT_VALUE_FOR_PARAMETER
   configuration: nnbd-strong
   script:
     - method1({int a}) {}

pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.outline.expect

@@ -22,7 +22,8 @@ library /*isNonNullableByDefault*/;
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //

pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.expect

@@ -22,7 +22,8 @@ library /*isNonNullableByDefault*/;
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //

pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.transformed.expect

@@ -22,7 +22,8 @@ library /*isNonNullableByDefault*/;
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //

pkg/front_end/testcases/nnbd/issue40954.dart.outline.expect

@@ -2,33 +2,39 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //

pkg/front_end/testcases/nnbd/issue40954.dart.strong.expect

@@ -2,33 +2,39 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //

pkg/front_end/testcases/nnbd/issue40954.dart.strong.transformed.expect

@@ -2,33 +2,39 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //

pkg/front_end/testcases/nnbd/issue40954.dart.weak.expect

@@ -2,33 +2,39 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //