Allow magic numbers for default values

lib/lints/no_magic_number/no_magic_number_rule.dart

@@ -69,7 +69,8 @@ class NoMagicNumberRule extends SolidLintRule<NoMagicNumberParameters> {
           .where(_isNotInsideConstConstructor)
           .where(_isNotInDateTime)
           .where(_isNotInsideIndexExpression)
-          .where(_isNotInsideEnumConstantArguments);
+          .where(_isNotInsideEnumConstantArguments)
+          .where(_isNotDefaultValue);
 
       for (final magicNumber in magicNumbers) {
         reporter.reportErrorForNode(code, magicNumber);
@@ -122,4 +123,8 @@ class NoMagicNumberRule extends SolidLintRule<NoMagicNumberParameters> {
       null;
 
   bool _isNotInsideIndexExpression(Literal l) => l.parent is! IndexExpression;
+
+  bool _isNotDefaultValue(Literal literal) {
+    return literal.thisOrAncestorOfType<DefaultFormalParameter>() == null;
+  }
 }

lint_test/no_magic_number_test.dart

@@ -1,4 +1,7 @@
-// ignore_for_file: unused_local_variable, prefer_match_file_name
+// ignore_for_file: unused_local_variable
+// ignore_for_file: prefer_match_file_name
+// ignore_for_file: avoid_unused_parameters
+// ignore_for_file: no_empty_block
 
 /// Check the `no_magic_number` rule
 
@@ -55,3 +58,20 @@ void fun() {
   // Allowed in DateTime because it doesn't have cons constructor
   final apocalypse = DateTime(2012, 12, 21);
 }
+
+// Allowed for defaults in constructors and methods.
+class DefaultValues {
+  final int value;
+
+  DefaultValues.named({
+    this.value = 2,
+  });
+
+  DefaultValues.positional([
+    this.value = 3,
+  ]);
+
+  void methodWithNamedParam({int value = 4}) {}
+
+  void methodWithPositionalParam([int value = 5]) {}
+}