Dart ignores non-nullability of variables and function parameters.

Dart VM version: 2.7.0-dev.2.1 (Mon Dec 2 20:10:59 2019 +0100) on "windows_x64"

The following test example tries to assign null values to non-nullable variables (if nnbd is enabled):

class A {
  void test(int i) { print(i); }
}

main() {
  int i;
  i = null;
  print(i);
  A().test(1);
  A().test(null);
}

It throws a compile error with analyzer and prints null variable values with dart.

As i is non-nullable, it seems like dart should throw compile errors for the lines 7 and 10 too.

Sample output is:

$> dartanalyzer --enable-experiment=non-nullable test.dart
Analyzing test.dart...
error - A value of type 'Null' can't be assigned to a variable of type 'int'. - test.dart:7:7 - invalid_assignment
error - The argument type 'Null' can't be assigned to the parameter type 'int'. - test.dart:10:12 - argument_type_not_assignable
2 errors found.

$> dart --enable-experiment=non-nullable test.dart
null
1
null

Thanks for your feedback, the non nullability language feature is still being implemented in the Dart VM and is not fully functional yet.

Quick status update on the CFE.

As of c85979a the CFE emits compile-time errors (or warnings, depending on the mode) for lines i = null; and A().test(null);. Here's how to test it:

Click to expand

$ cat /tmp/asdf.dart
class A {
  void test(int i) { print(i); }
}

main() {
  int i;
  i = null;
  print(i);
  A().test(1);
  A().test(null);
}

$ sdk/bin/dart pkg/front_end/tool/fasta.dart compile --dump-ir -o /dev/null --enable-experiment=non-nullable --force-nnbd-checks --nnbd-strong /tmp/asdf.dart
Running: .../sdk/bin/dart --enable-asserts .../pkg/front_end/tool/_fasta/compile.dart --dump-ir -o /dev/null --enable-experiment=non-nullable --force-nnbd-checks --nnbd-strong /tmp/asdf.dart
/tmp/asdf.dart:7:7: Error: A value of type 'Null?' can't be assigned to a variable of type 'int'.
  i = null;
      ^
/tmp/asdf.dart:10:12: Error: The argument type 'Null?' can't be assigned to the parameter type 'int'.
  A().test(null);
           ^
library;
//
// Problems in library:
//
// /tmp/asdf.dart:7:7: Error: A value of type 'Null?' can't be assigned to a variable of type 'int'.
//   i = null;
//       ^
//
// /tmp/asdf.dart:10:12: Error: The argument type 'Null?' can't be assigned to the parameter type 'int'.
//   A().test(null);
//            ^
//
import self as self;
import "dart:core" as core;

class A extends core::Object {
  synthetic constructor •() → self::A
    : super core::Object::•()
    ;
  method test(core::int i) → void {
    core::print(i);
  }
}
static method main() → dynamic {
  core::int i;
  i = let final<BottomType> #t1 = invalid-expression "/tmp/asdf.dart:7:7: Error: A value of type 'Null?' can't be assigned to a variable of type 'int'.\n  i = null;\n      ^" in null as{TypeError} core::int;
  core::print(i);
  new self::A::•().{self::A::test}(1);
  new self::A::•().{self::A::test}(let final<BottomType> #t2 = invalid-expression "/tmp/asdf.dart:10:12: Error: The argument type 'Null?' can't be assigned to the parameter type 'int'.\n  A().test(null);\n           ^" in null as{TypeError} core::int);
}

To compile in weak mode, remove flag --nnbd-strong:

Click to expand

$ sdk/bin/dart pkg/front_end/tool/fasta.dart compile --dump-ir -o /dev/null --enable-experiment=non-nullable --force-nnbd-checks /tmp/asdf.dart
Running: .../sdk/bin/dart --enable-asserts .../pkg/front_end/tool/_fasta/compile.dart --dump-ir -o /dev/null --enable-experiment=non-nullable --force-nnbd-checks /tmp/asdf.dart
/tmp/asdf.dart:7:3: Warning: Assigning value of type 'Null?' to a variable of type 'int'.
  i = null;
  ^
/tmp/asdf.dart:10:12: Warning: Assigning value of type 'Null?' to a variable of type 'int'.
  A().test(null);
           ^
library;
//
// Problems in library:
//
// /tmp/asdf.dart:7:3: Warning: Assigning value of type 'Null?' to a variable of type 'int'.
//   i = null;
//   ^
//
// /tmp/asdf.dart:10:12: Warning: Assigning value of type 'Null?' to a variable of type 'int'.
//   A().test(null);
//            ^
//
import self as self;
import "dart:core" as core;

class A extends core::Object {
  synthetic constructor •() → self::A
    : super core::Object::•()
    ;
  method test(core::int i) → void {
    core::print(i);
  }
}
static method main() → dynamic {
  core::int i;
  i = null;
  core::print(i);
  new self::A::•().{self::A::test}(1);
  new self::A::•().{self::A::test}(null);
}

Removing the front-end label as this should be considered a vm issue now.

@stefantsov

@stefantsov Is the flag --force-nnbd-checks required to get these errors, because I checked and the VM does pass the --enable-experiment=non-nullable flag to the front end and it does not seem to report any errors.

NNBD specific warnings and errors still require the --force-nnbd-checks. We plan to remove this flag once VM and DDC can build the nnbd sdk cleanly with warnings/errors enabled.

Is this still blocking unfork? Can we move this under #40106 ?

Yes this is not blocking the unfork, I have moved into the Dart VM support for Null safe feature project.

This requires the --force-nnbd-checks guard to be removed from the front end (please see issue #40980).
Closing as a duplicate of that issue.

Navigation Menu

Repository navigation

Dart ignores non-nullability of variables and function parameters. #39678

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Dart ignores non-nullability of variables and function parameters. #39678

Description

Activity

a-siva commented on Dec 7, 2019

chloestefantsova commented on Dec 16, 2019

johnniwinther commented on Jan 13, 2020

a-siva commented on Feb 6, 2020

johnniwinther commented on Feb 6, 2020

franklinyow commented on Mar 2, 2020

a-siva commented on Mar 2, 2020

a-siva commented on Mar 11, 2020

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions