feat: add allow-only-once option to no-magic-number rule (#1173)

* feat: add allow-only-once option to no-magic-number

* chore: update changelog

* fix: after review

Author: san-smith

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * fix: export missing parts of public API.
 * feat: support `context.mounted` for [`use-setstate-synchronously`](https://dcm.dev/docs/individuals/rules/flutter/use-setstate-synchronously).
+* feat: add `allow-only-once` option to [`no-magic-number`](https://dcm.dev/docs/individuals/rules/common/no-magic-number).
 
 ## 5.5.0
 

lib/src/analyzers/lint_analyzer/rules/rules_list/no_magic_number/config_parser.dart

@@ -3,9 +3,14 @@ part of 'no_magic_number_rule.dart';
 class _ConfigParser {
   static const _allowedConfigName = 'allowed';
 
+  static const _allowOnlyOnce = 'allow-only-once';
+
   static const _defaultMagicNumbers = [-1, 0, 1];
 
   static Iterable<num> parseAllowedNumbers(Map<String, Object> config) =>
       (config[_allowedConfigName] as Iterable?)?.cast<num>() ??
       _defaultMagicNumbers;
+
+  static bool parseAllowOnlyOnce(Map<String, Object> config) =>
+      (config[_allowOnlyOnce] as bool?) ?? false;
 }

lib/src/analyzers/lint_analyzer/rules/rules_list/no_magic_number/no_magic_number_rule.dart

@@ -21,9 +21,11 @@ class NoMagicNumberRule extends CommonRule {
       'Avoid using magic numbers. Extract them to named constants or variables.';
 
   final Iterable<num> _allowedMagicNumbers;
+  final bool _allowOnlyOnce;
 
   NoMagicNumberRule([Map<String, Object> config = const {}])
       : _allowedMagicNumbers = _ConfigParser.parseAllowedNumbers(config),
+        _allowOnlyOnce = _ConfigParser.parseAllowOnlyOnce(config),
         super(
           id: ruleId,
           severity: readSeverity(config, Severity.warning),
@@ -45,7 +47,11 @@ class NoMagicNumberRule extends CommonRule {
 
     source.unit.visitChildren(visitor);
 
-    return visitor.literals
+    final literals = _allowOnlyOnce
+        ? _getNotSingleLiterals(visitor.literals)
+        : visitor.literals;
+
+    return literals
         .where(_isMagicNumber)
         .where(_isNotInsideVariable)
         .where(_isNotInsideCollectionLiteral)
@@ -62,6 +68,24 @@ class NoMagicNumberRule extends CommonRule {
         .toList(growable: false);
   }
 
+  Iterable<Literal> _getNotSingleLiterals(Iterable<Literal> literals) {
+    final literalsCount = <num, int>{};
+    for (final l in literals) {
+      if (l is IntegerLiteral) {
+        final value = l.value;
+        if (value != null) {
+          literalsCount.update(value, (count) => ++count, ifAbsent: () => 1);
+        }
+      } else if (l is DoubleLiteral) {
+        literalsCount.update(l.value, (count) => ++count, ifAbsent: () => 1);
+      }
+    }
+
+    return literals.where((l) =>
+        l is IntegerLiteral && literalsCount[l.value] != 1 ||
+        l is DoubleLiteral && literalsCount[l.value] != 1);
+  }
+
   bool _isMagicNumber(Literal l) =>
       (l is DoubleLiteral && !_allowedMagicNumbers.contains(l.value)) ||
       (l is IntegerLiteral && !_allowedMagicNumbers.contains(l.value));

test/src/analyzers/lint_analyzer/rules/rules_list/no_magic_number/no_magic_number_rule_test.dart

@@ -68,6 +68,22 @@ void main() {
       RuleTestHelper.verifyNoIssues(issues);
     });
 
+    test('reports magic numbers used more than once', () async {
+      final unit = await RuleTestHelper.resolveFromFile(_incorrectExamplePath);
+      final config = {
+        'allow-only-once': true,
+      };
+
+      final issues = NoMagicNumberRule(config).check(unit);
+
+      RuleTestHelper.verifyIssues(
+        issues: issues,
+        startLines: [2, 4],
+        startColumns: [28, 25],
+        locationTexts: ['12', '12'],
+      );
+    });
+
     test(
       'reports magic numbers in objects in widget array structures',
       () async {

website/docs/rules/common/no-magic-number.mdx

@@ -56,4 +56,5 @@ dart_code_metrics:
     ...
     - no-magic-number:
         allowed: [3.14, 100, 12]
+        allow-only-once: true
 ```