[pigeon] Remove support for non-NNBD (#1524)

Makes a breaking change to remove non-NNBD support, since it adds complexity
to the generator and there's no compelling reason to continue supporting it going
forward.

Also updates some legacy Dart commands in scripts (dartanalyzer, dart pub run)
to their modern versions.

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 3.0.0
+
+* **BREAKING CHANGE**: Removes the `--dart_null_safety` flag. Generated Dart
+  now always uses nullability annotations, and thus requires Dart 2.12 or later.
+
 ## 2.0.4
 
 * Fixes bug where Dart `FlutterApi`s would assert that a nullable argument was nonnull.
@@ -9,7 +14,7 @@
 ## 2.0.2
 
 * Fixes Java crash for nullable nested type.
-  
+
 * ## 2.0.1
 
 * Adds support for TaskQueues for serial background execution.

packages/pigeon/lib/generator_tools.dart

@@ -8,7 +8,7 @@ import 'dart:mirrors';
 import 'ast.dart';
 
 /// The current version of pigeon. This must match the version in pubspec.yaml.
-const String pigeonVersion = '2.0.4';
+const String pigeonVersion = '3.0.0';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/lib/pigeon_lib.dart

@@ -1041,9 +1041,6 @@ options:
     ..addOption('java_out', help: 'Path to generated Java file (.java).')
     ..addOption('java_package',
         help: 'The package that generated Java code will be in.')
-    ..addFlag('dart_null_safety',
-        help: 'Makes generated Dart code have null safety annotations',
-        defaultsTo: true)
     ..addOption('objc_header_out',
         help: 'Path to generated Objective-C header file (.h).')
     ..addOption('objc_prefix',
@@ -1082,9 +1079,6 @@ options:
       javaOptions: JavaOptions(
         package: results['java_package'],
       ),
-      dartOptions: DartOptions(
-        isNullSafe: results['dart_null_safety'],
-      ),
       copyrightHeader: results['copyright_header'],
       oneLanguage: results['one_language'],
       astOut: results['ast_out'],

packages/pigeon/pubspec.yaml

@@ -2,7 +2,7 @@ name: pigeon
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/main/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3Apigeon
-version: 2.0.4 # This must match the version in lib/generator_tools.dart
+version: 3.0.0 # This must match the version in lib/generator_tools.dart
 
 environment:
   sdk: ">=2.12.0 <3.0.0"

packages/pigeon/run_tests.sh

@@ -86,38 +86,26 @@ test_pigeon_android() {
 # test_null_safe_dart(<path to pigeon file>)
 #
 # Compiles the pigeon file to a temp directory and attempts to run the dart
-# analyzer on it with and without null safety turned on.
+# analyzer on it.
 test_pigeon_dart() {
   echo "test_pigeon_dart($1)"
-  temp_dir_1=$(mktmpdir)
-  temp_dir_2=$(mktmpdir)
-
-  $run_pigeon \
-    --input $1 \
-    --dart_out $temp_dir_1/pigeon.dart &
-  null_safe_gen_pid=$!
+  temp_dir=$(mktmpdir)
 
   $run_pigeon \
-    --no-dart_null_safety \
     --input $1 \
-    --dart_out $temp_dir_2/pigeon.dart &
-  non_null_safe_gen_pid=$!
+    --dart_out $temp_dir/pigeon.dart &
+  gen_pid=$!
 
-  wait $null_safe_gen_pid
-  wait $non_null_safe_gen_pid
+  wait $gen_pid
 
   # `./e2e_tests/test_objc/.packages` is used to get access to Flutter since
   # Pigeon doesn't depend on Flutter.
-  dartanalyzer $temp_dir_1/pigeon.dart --fatal-infos --fatal-warnings --packages ./e2e_tests/test_objc/.packages &
-  null_safe_analyze_pid=$!
-  dartanalyzer $temp_dir_2/pigeon.dart --fatal-infos --fatal-warnings --packages ./e2e_tests/test_objc/.packages &
-  non_null_safe_analyze_pid=$!
+  dart analyze $temp_dir/pigeon.dart --fatal-infos --fatal-warnings --packages ./e2e_tests/test_objc/.packages &
+  analyze_pid=$!
 
-  wait $null_safe_analyze_pid
-  wait $non_null_safe_analyze_pid
+  wait $analyze_pid
 
-  rm -rf $temp_dir_1
-  rm -rf $temp_dir_2
+  rm -rf $temp_dir
 }
 
 print_usage() {
@@ -184,7 +172,7 @@ get_java_linter_formatter() {
 }
 
 run_dart_unittests() {
-  dart pub run pigeon:run_tests -t dart_unittests
+  dart run pigeon:run_tests -t dart_unittests
 }
 
 test_command_line() {
@@ -204,11 +192,11 @@ test_command_line() {
 }
 
 run_flutter_unittests() {
-  dart pub run pigeon:run_tests -t flutter_unittests
+  dart run pigeon:run_tests -t flutter_unittests
 }
 
 run_mock_handler_tests() {
-  dart pub run pigeon:run_tests -t mock_handler_tests
+  dart run pigeon:run_tests -t mock_handler_tests
 }
 
 run_dart_compilation_tests() {