Add a lint for missing files in conditional imports

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 1.16.0
+
+- new lint: `conditional_uri_does_not_exist`
+
 # 1.15.0
 
 - new lint: `use_decorated_box`

example/all.yaml

@@ -57,6 +57,7 @@ linter:
     - cast_nullable_to_non_nullable
     - close_sinks
     - comment_references
+    - conditional_uri_does_not_exist
     - constant_identifier_names
     - control_flow_in_finally
     - curly_braces_in_flow_control_structures

lib/src/rules.dart

@@ -59,6 +59,7 @@ import 'rules/cascade_invocations.dart';
 import 'rules/cast_nullable_to_non_nullable.dart';
 import 'rules/close_sinks.dart';
 import 'rules/comment_references.dart';
+import 'rules/conditional_uri_does_not_exist.dart';
 import 'rules/constant_identifier_names.dart';
 import 'rules/control_flow_in_finally.dart';
 import 'rules/curly_braces_in_flow_control_structures.dart';
@@ -264,6 +265,7 @@ void registerLintRules({bool inTestMode = false}) {
     ..register(CastNullableToNonNullable())
     ..register(CloseSinks())
     ..register(CommentReferences())
+    ..register(ConditionalUriDoesNotExist())
     ..register(ConstantIdentifierNames())
     ..register(ControlFlowInFinally())
     ..register(CurlyBracesInFlowControlStructures())

lib/src/rules/conditional_uri_does_not_exist.dart

@@ -0,0 +1,73 @@
+// Copyright (c) 2021, 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.
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+import '../analyzer.dart';
+
+const _desc = r'Missing conditional import.';
+
+const _details = r'''
+
+**DON'T** reference files that do not exist in conditional imports.
+
+Code may fail at runtime if the condition evaluates such that the missing file
+needs to be imported.
+
+**BAD:**
+```dart
+import 'file_that_does_exist.dart'
+  if (condition) 'file_that_does_not_exist.dart';
+```
+
+**GOOD:**
+```dart
+import 'file_that_does_exist.dart'
+  if (condition) 'file_that_also_does_exist.dart';
+```
+
+''';
+
+class ConditionalUriDoesNotExist extends LintRule {
+  ConditionalUriDoesNotExist()
+      : super(
+            name: 'conditional_uri_does_not_exist',
+            description: _desc,
+            details: _details,
+            group: Group.style);
+
+  @override
+  void registerNodeProcessors(
+      NodeLintRegistry registry, LinterContext context) {
+    var visitor = _Visitor(this);
+    registry.addConfiguration(this, visitor);
+  }
+}
+
+class _Visitor extends SimpleAstVisitor<void> {
+  static const LintCode code = LintCode('conditional_uri_does_not_exist',
+      "The target of the conditional URI '{0}' doesn't exist.",
+      correctionMessage: 'Try creating the file referenced by the URI, or '
+          'try using a URI for a file that does exist.');
+
+  final LintRule rule;
+
+  _Visitor(this.rule);
+
+  @override
+  void visitConfiguration(Configuration configuration) {
+    String? uriContent = configuration.uri.stringValue;
+    if (uriContent != null) {
+      Source? source = configuration.uriSource;
+      // Checking source with .exists() will not detect the presence of overlays
+      // in the analysis server (although running the script when the files
+      // don't exist on disk would also fail to find it).
+      if (!(source?.exists() ?? false)) {
+        rule.reportLint(configuration.uri,
+            arguments: [uriContent], errorCode: code);
+      }
+    }
+  }
+}

test/rule_test_support.dart

@@ -86,7 +86,7 @@ class ExpectedDiagnostic {
     if (!diagnosticMatcher(error)) return false;
     if (error.offset != offset) return false;
     if (error.length != length) return false;
-    if (messageContains != null && error.message.contains(messageContains!)) {
+    if (messageContains != null && !error.message.contains(messageContains!)) {
       return false;
     }
 

test/rules/all.dart

@@ -7,6 +7,7 @@ import 'avoid_function_literals_in_foreach_calls.dart'
 import 'avoid_init_to_null.dart' as avoid_init_to_null;
 import 'avoid_shadowing_type_parameters.dart'
     as avoid_shadowing_type_parameters;
+import 'conditional_uri_does_not_exist.dart' as conditional_uri_does_not_exist;
 import 'file_names.dart' as file_names;
 import 'literal_only_boolean_expressions.dart'
     as literal_only_boolean_expressions;
@@ -39,6 +40,7 @@ void main() {
   avoid_function_literals_in_foreach_calls.main();
   avoid_init_to_null.main();
   avoid_shadowing_type_parameters.main();
+  conditional_uri_does_not_exist.main();
   file_names.main();
   literal_only_boolean_expressions.main();
   missing_whitespace_between_adjacent_strings.main();

test/rules/conditional_uri_does_not_exist.dart

@@ -0,0 +1,78 @@
+// Copyright (c) 2021, 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.
+
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../rule_test_support.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ConditionalUriDoesNotExistTest);
+  });
+}
+
+@reflectiveTest
+class ConditionalUriDoesNotExistTest extends LintRuleTest {
+  @override
+  bool get addMetaPackageDep => true;
+
+  @override
+  String get lintRule => 'conditional_uri_does_not_exist';
+
+  test_missingDartLibraries() async {
+    await assertDiagnostics(
+      r'''
+import ''
+    if (dart.library.io) 'dart:missing_1'
+    if (dart.library.html) 'dart:async'
+    if (dart.library.async) 'dart:missing_2';
+''',
+      [
+        error(HintCode.UNUSED_IMPORT, 7, 2),
+        lint('conditional_uri_does_not_exist', 35, 16,
+            messageContains: 'dart:missing_1'),
+        lint('conditional_uri_does_not_exist', 120, 16,
+            messageContains: 'dart:missing_2'),
+      ],
+    );
+  }
+
+  test_missingFiles() async {
+    newFile('$testPackageRootPath/lib/exists.dart');
+
+    await assertDiagnostics(
+      r'''
+import ''
+    if (dart.library.io) 'missing_1.dart'
+    if (dart.library.html) 'exists.dart'
+    if (dart.library.async) 'missing_2.dart';
+''',
+      [
+        error(HintCode.UNUSED_IMPORT, 7, 2),
+        lint('conditional_uri_does_not_exist', 35, 16,
+            messageContains: 'missing_1.dart'),
+        lint('conditional_uri_does_not_exist', 121, 16,
+            messageContains: 'missing_2.dart'),
+      ],
+    );
+  }
+
+  test_missingPackages() async {
+    await assertDiagnostics(
+      r'''
+import ''
+    if (dart.library.io) 'package:meta/missing_1.dart'
+    if (dart.library.html) 'package:meta/meta.dart'
+    if (dart.library.io) 'package:foo/missing_2.dart';
+''',
+      [
+        error(HintCode.UNUSED_IMPORT, 7, 2),
+        lint('conditional_uri_does_not_exist', 35, 29,
+            messageContains: 'missing_1.dart'),
+        lint('conditional_uri_does_not_exist', 142, 28,
+            messageContains: 'missing_2.dart'),
+      ],
+    );
+  }
+}

tool/since/linter.yaml

@@ -51,6 +51,7 @@ cascade_invocations: 0.1.29
 cast_nullable_to_non_nullable : 0.1.120
 close_sinks: 0.1.19
 comment_references: 0.1.17
+conditional_uri_does_not_exist: 1.16.0
 control_flow_in_finally: 0.1.16
 constant_identifier_names: 0.1.1
 curly_braces_in_flow_control_structures: 0.1.57