Add a lint for missing files in conditional imports

CHANGELOG.md

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

example/all.yaml

@@ -84,6 +84,7 @@ linter:
     - lines_longer_than_80_chars
     - list_remove_unrelated_type
     - literal_only_boolean_expressions
+    - missing_conditional_import
     - missing_whitespace_between_adjacent_strings
     - no_adjacent_strings_in_list
     - no_default_cases

lib/src/rules.dart

@@ -86,6 +86,7 @@ import 'rules/library_private_types_in_public_api.dart';
 import 'rules/lines_longer_than_80_chars.dart';
 import 'rules/list_remove_unrelated_type.dart';
 import 'rules/literal_only_boolean_expressions.dart';
+import 'rules/missing_conditional_import.dart';
 import 'rules/missing_whitespace_between_adjacent_strings.dart';
 import 'rules/no_adjacent_strings_in_list.dart';
 import 'rules/no_default_cases.dart';
@@ -291,6 +292,7 @@ void registerLintRules({bool inTestMode = false}) {
     ..register(LinesLongerThan80Chars())
     ..register(ListRemoveUnrelatedType())
     ..register(LiteralOnlyBooleanExpressions())
+    ..register(MissingConditionalImport())
     ..register(MissingWhitespaceBetweenAdjacentStrings())
     ..register(NoAdjacentStringsInList())
     ..register(NoDefaultCases())

lib/src/rules/missing_conditional_import.dart

@@ -0,0 +1,70 @@
+// 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_not_exist.dart';
+```
+
+**GOOD:**
+```dart
+import 'file_that_exists.dart';
+```
+
+''';
+
+class MissingConditionalImport extends LintRule {
+  MissingConditionalImport()
+      : super(
+            name: 'missing_conditional_import',
+            description: _desc,
+            details: _details,
+            group: Group.style);
+
+  @override
+  void registerNodeProcessors(
+      NodeLintRegistry registry, LinterContext context) {
+    var visitor = _Visitor(this);
+    registry.addCompilationUnit(this, visitor);
+  }
+}
+
+class _Visitor extends RecursiveAstVisitor<void> {
+  static const LintCode code = LintCode('missing_conditional_import',
+      "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;
+      if (!(source?.exists() ?? false)) {
+        rule.reportLint(configuration.uri,
+            arguments: [uriContent], errorCode: code);
+      }
+    }
+
+    super.visitConfiguration(configuration);
+  }
+}

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

@@ -10,6 +10,7 @@ import 'avoid_shadowing_type_parameters.dart'
 import 'file_names.dart' as file_names;
 import 'literal_only_boolean_expressions.dart'
     as literal_only_boolean_expressions;
+import 'missing_conditional_import.dart' as missing_conditional_import;
 import 'missing_whitespace_between_adjacent_strings.dart'
     as missing_whitespace_between_adjacent_strings;
 import 'non_constant_identifier_names.dart' as non_constant_identifier_names;
@@ -41,6 +42,7 @@ void main() {
   avoid_shadowing_type_parameters.main();
   file_names.main();
   literal_only_boolean_expressions.main();
+  missing_conditional_import.main();
   missing_whitespace_between_adjacent_strings.main();
   non_constant_identifier_names.main();
   null_closures.main();

test/rules/missing_conditional_import.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(MissingConditionalImportTest);
+  });
+}
+
+@reflectiveTest
+class MissingConditionalImportTest extends LintRuleTest {
+  @override
+  bool get addMetaPackageDep => true;
+
+  @override
+  String get lintRule => 'missing_conditional_import';
+
+  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('missing_conditional_import', 35, 16,
+            messageContains: 'dart:missing_1'),
+        lint('missing_conditional_import', 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('missing_conditional_import', 35, 16,
+            messageContains: 'missing_1.dart'),
+        lint('missing_conditional_import', 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('missing_conditional_import', 35, 29,
+            messageContains: 'missing_1.dart'),
+        lint('missing_conditional_import', 142, 28,
+            messageContains: 'missing_2.dart'),
+      ],
+    );
+  }
+}

tool/since/linter.yaml

@@ -74,6 +74,7 @@ library_prefixes: 0.1.1
 lines_longer_than_80_chars: 0.1.56
 list_remove_unrelated_type: 0.1.22
 literal_only_boolean_expressions: 0.1.25
+missing_conditional_import: 1.16.0
 missing_whitespace_between_adjacent_strings : 0.1.110
 no_adjacent_strings_in_list: 0.1.30
 no_default_cases : 0.1.116