Add null-unsoundness check to print's object.toString() result.

This makes it an *earlier* error if a `toString` method returns `null` when passed to `print`, possibly a new error if the underlying platform's print implementation let `null` through. Returning `null` is something `toString` was never supposed to do, and with null safety, it's enforced by the type system, so only pre-null-safety legacy code can actually return `null`. Makes the error message from `NotNullableError` not assume a parameter, so it can be used in more places. Bug: #47196 Change-Id: I7f10156330994d31e44384fa952dd88385e2628d Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/214043 Reviewed-by: Nate Bosch <[email protected]> Commit-Queue: Lasse R.H. Nielsen <[email protected]>
dart-lang · Sep 23, 2021 · 651d6e0 · 651d6e0
1 parent 65184a9
commit 651d6e0
Show file tree

Hide file tree

Showing 2 changed files with 2 additions and 3 deletions.
diff --git a/sdk/lib/core/print.dart b/sdk/lib/core/print.dart
@@ -6,7 +6,7 @@ part of dart.core;
 
 /// Prints a string representation of the object to the console.
 void print(Object? object) {
-  String line = object.toString();
+  String line = checkNotNullable(object.toString(), "object.toString()");
   var toZone = printToZone;
   if (toZone == null) {
     printToConsole(line);

diff --git a/sdk/lib/internal/internal.dart b/sdk/lib/internal/internal.dart
@@ -749,8 +749,7 @@ T checkNotNullable<T extends Object>(T value, String name) {
 class NotNullableError<T> extends Error implements TypeError {
   final String _name;
   NotNullableError(this._name);
-  String toString() =>
-      "Null is not a valid value for the parameter '$_name' of type '$T'";
+  String toString() => "Null is not a valid value for '$_name' of type '$T'";
 }
 
 /// A function that returns the value or default value (if invoked with `null`