Add language_2 tests covering some cases of definite assignment.

This CL is intentionally light on coverage, because we put most of
testing in analyzer unit / functional tests.

This CL intentionally does not use multi-tests, because they are
harder to read.

R=brianwilkerson@google.com, paulberry@google.com

Change-Id: Ib48cd02fc93a9d7f8cfa3803d0c51e96c013a99f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107197
Reviewed-by: Paul Berry <paulberry@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

tests/language_2/nnbd/static_errors/not_assigned_local_if_then_else_else_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v; //# none: compile-time error
+  if (b) {
+    // not assigned
+  } else {
+    v = 1;
+  }
+  v;
+}
+
+void main() {}

tests/language_2/nnbd/static_errors/not_assigned_local_if_then_else_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v;
+  if (b) {
+    v = 0;
+  } else {
+    v = 1;
+  }
+  v;
+}
+
+void main() {}

tests/language_2/nnbd/static_errors/not_assigned_local_if_then_else_then_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v; //# none: compile-time error
+  if (b) {
+    v = 0;
+  } else {
+    // not assigned
+  }
+  v;
+}
+
+void main() {}

tests/language_2/nnbd/static_errors/not_assigned_local_if_then_test.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v; //# none: compile-time error
+  if (b) {
+    v = 0;
+  }
+  v;
+}
+
+void main() {}

tests/language_2/nnbd/static_errors/not_assigned_local_try_catch_body_catch_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+void main() {
+  int v;
+  try {
+    g();
+    v = 0;
+  } catch (_) {
+    v = 1;
+  }
+  v;
+}
+
+void g() {}

tests/language_2/nnbd/static_errors/not_assigned_local_try_catch_body_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+void main() {
+  int v; //# none: compile-time error
+  try {
+    g();
+    v = 0;
+  } catch (_) {
+    // not assigned
+  }
+  v;
+}
+
+void g() {}

tests/language_2/nnbd/static_errors/not_assigned_local_while_true_break_after_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v;
+  while (true) {
+    v = 0;
+    if (b) break;
+  }
+  v;
+}
+
+void main() {}

tests/language_2/nnbd/static_errors/not_assigned_local_while_true_break_before_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=non-nullable
+
+// It is an error if a potentially non-nullable local variable which has no
+// initializer expression and is not marked `late` is used before it is
+// definitely assigned.
+
+f(bool b) {
+  int v; //# none: compile-time error
+  while (true) {
+    if (b) break;
+    v = 0;
+  }
+  v;
+}
+
+void main() {}