Fix newly enforced package:pedantic lints (flutter#19)

- always_declare_return_types
- annotate_overrides
- prefer_conditional_assignment
- prefer_if_null_operators
- prefer_single_quotes
- use_function_type_syntax_for_parameters

Drop unused author field from pubspec.

Simplify dependency on `string_scanner` since older versions aren't
supported on the Dart 2 SDK and so wouldn't be picked up even with a
wide constraint.

Author: natebosch

example/example.dart

@@ -1,6 +1,6 @@
 import 'package:boolean_selector/boolean_selector.dart';
 
 void main(List<String> args) {
-  var selector = BooleanSelector.parse("(x && y) || z");
+  var selector = BooleanSelector.parse('(x && y) || z');
   print(selector.evaluate((variable) => args.contains(variable)));
 }

lib/boolean_selector.dart

@@ -54,5 +54,5 @@ abstract class BooleanSelector {
   ///
   /// The [isDefined] function should return `true` for any variables that are
   /// considered valid, and `false` for any invalid or undefined variables.
-  void validate(bool isDefined(String variable));
+  void validate(bool Function(String variable) isDefined);
 }

lib/src/all.dart

@@ -8,17 +8,23 @@ import '../boolean_selector.dart';
 class All implements BooleanSelector {
   // TODO(nweiz): Stop explicitly providing a type argument when sdk#32412 is
   // fixed.
+  @override
   final variables = const <String>[];
 
   const All();
 
+  @override
   bool evaluate(semantics) => true;
 
+  @override
   BooleanSelector intersection(BooleanSelector other) => other;
 
+  @override
   BooleanSelector union(BooleanSelector other) => this;
 
-  void validate(bool isDefined(String variable)) {}
+  @override
+  void validate(bool Function(String variable) isDefined) {}
 
-  String toString() => "<all>";
+  @override
+  String toString() => '<all>';
 }

lib/src/ast.dart

@@ -21,52 +21,65 @@ abstract class Node {
   Iterable<String> get variables;
 
   /// Calls the appropriate [Visitor] method on [this] and returns the result.
-  accept(Visitor visitor);
+  dynamic accept(Visitor visitor);
 }
 
 /// A single variable.
 class VariableNode implements Node {
+  @override
   final FileSpan span;
 
   /// The variable name.
   final String name;
 
+  @override
   Iterable<String> get variables => [name];
 
   VariableNode(this.name, [this.span]);
 
-  accept(Visitor visitor) => visitor.visitVariable(this);
+  @override
+  dynamic accept(Visitor visitor) => visitor.visitVariable(this);
 
+  @override
   String toString() => name;
 
+  @override
   bool operator ==(other) => other is VariableNode && name == other.name;
 
+  @override
   int get hashCode => name.hashCode;
 }
 
 /// A negation expression.
 class NotNode implements Node {
+  @override
   final FileSpan span;
 
   /// The expression being negated.
   final Node child;
 
+  @override
   Iterable<String> get variables => child.variables;
 
   NotNode(this.child, [this.span]);
 
-  accept(Visitor visitor) => visitor.visitNot(this);
+  @override
+  dynamic accept(Visitor visitor) => visitor.visitNot(this);
 
+  @override
   String toString() =>
-      child is VariableNode || child is NotNode ? "!$child" : "!($child)";
+      child is VariableNode || child is NotNode ? '!$child' : '!($child)';
 
+  @override
   bool operator ==(other) => other is NotNode && child == other.child;
 
+  @override
   int get hashCode => ~child.hashCode;
 }
 
 /// An or expression.
 class OrNode implements Node {
+  @override
   FileSpan get span => _expandSafe(left.span, right.span);
 
   /// The left-hand branch of the expression.
@@ -75,31 +88,37 @@ class OrNode implements Node {
   /// The right-hand branch of the expression.
   final Node right;
 
+  @override
   Iterable<String> get variables sync* {
     yield* left.variables;
     yield* right.variables;
   }
 
   OrNode(this.left, this.right);
 
-  accept(Visitor visitor) => visitor.visitOr(this);
+  @override
+  dynamic accept(Visitor visitor) => visitor.visitOr(this);
 
+  @override
   String toString() {
-    var string1 = left is AndNode || left is ConditionalNode ? "($left)" : left;
+    var string1 = left is AndNode || left is ConditionalNode ? '($left)' : left;
     var string2 =
-        right is AndNode || right is ConditionalNode ? "($right)" : right;
+        right is AndNode || right is ConditionalNode ? '($right)' : right;
 
-    return "$string1 || $string2";
+    return '$string1 || $string2';
   }
 
+  @override
   bool operator ==(other) =>
       other is OrNode && left == other.left && right == other.right;
 
+  @override
   int get hashCode => left.hashCode ^ right.hashCode;
 }
 
 /// An and expression.
 class AndNode implements Node {
+  @override
   FileSpan get span => _expandSafe(left.span, right.span);
 
   /// The left-hand branch of the expression.
@@ -108,31 +127,37 @@ class AndNode implements Node {
   /// The right-hand branch of the expression.
   final Node right;
 
+  @override
   Iterable<String> get variables sync* {
     yield* left.variables;
     yield* right.variables;
   }
 
   AndNode(this.left, this.right);
 
-  accept(Visitor visitor) => visitor.visitAnd(this);
+  @override
+  dynamic accept(Visitor visitor) => visitor.visitAnd(this);
 
+  @override
   String toString() {
-    var string1 = left is OrNode || left is ConditionalNode ? "($left)" : left;
+    var string1 = left is OrNode || left is ConditionalNode ? '($left)' : left;
     var string2 =
-        right is OrNode || right is ConditionalNode ? "($right)" : right;
+        right is OrNode || right is ConditionalNode ? '($right)' : right;
 
-    return "$string1 && $string2";
+    return '$string1 && $string2';
   }
 
+  @override
   bool operator ==(other) =>
       other is AndNode && left == other.left && right == other.right;
 
+  @override
   int get hashCode => left.hashCode ^ right.hashCode;
 }
 
 /// A ternary conditional expression.
 class ConditionalNode implements Node {
+  @override
   FileSpan get span => _expandSafe(condition.span, whenFalse.span);
 
   /// The condition expression to check.
@@ -144,6 +169,7 @@ class ConditionalNode implements Node {
   /// The branch to run if the condition is false.
   final Node whenFalse;
 
+  @override
   Iterable<String> get variables sync* {
     yield* condition.variables;
     yield* whenTrue.variables;
@@ -152,21 +178,25 @@ class ConditionalNode implements Node {
 
   ConditionalNode(this.condition, this.whenTrue, this.whenFalse);
 
-  accept(Visitor visitor) => visitor.visitConditional(this);
+  @override
+  dynamic accept(Visitor visitor) => visitor.visitConditional(this);
 
+  @override
   String toString() {
     var conditionString =
-        condition is ConditionalNode ? "($condition)" : condition;
-    var trueString = whenTrue is ConditionalNode ? "($whenTrue)" : whenTrue;
-    return "$conditionString ? $trueString : $whenFalse";
+        condition is ConditionalNode ? '($condition)' : condition;
+    var trueString = whenTrue is ConditionalNode ? '($whenTrue)' : whenTrue;
+    return '$conditionString ? $trueString : $whenFalse';
   }
 
+  @override
   bool operator ==(other) =>
       other is ConditionalNode &&
       condition == other.condition &&
       whenTrue == other.whenTrue &&
       whenFalse == other.whenFalse;
 
+  @override
   int get hashCode =>
       condition.hashCode ^ whenTrue.hashCode ^ whenFalse.hashCode;
 }

lib/src/evaluator.dart

@@ -18,16 +18,21 @@ class Evaluator implements Visitor<bool> {
             ? semantics.toSet().contains
             : semantics as _Semantics;
 
+  @override
   bool visitVariable(VariableNode node) => _semantics(node.name);
 
+  @override
   bool visitNot(NotNode node) => !node.child.accept(this);
 
+  @override
   bool visitOr(OrNode node) =>
       node.left.accept(this) || node.right.accept(this);
 
+  @override
   bool visitAnd(AndNode node) =>
       node.left.accept(this) && node.right.accept(this);
 
+  @override
   bool visitConditional(ConditionalNode node) => node.condition.accept(this)
       ? node.whenTrue.accept(this)
       : node.whenFalse.accept(this);

lib/src/impl.dart

@@ -28,10 +28,13 @@ class BooleanSelectorImpl implements BooleanSelector {
 
   BooleanSelectorImpl._(this._selector);
 
+  @override
   Iterable<String> get variables => _selector.variables;
 
+  @override
   bool evaluate(semantics) => _selector.accept(Evaluator(semantics));
 
+  @override
   BooleanSelector intersection(BooleanSelector other) {
     if (other == BooleanSelector.all) return this;
     if (other == BooleanSelector.none) return other;
@@ -40,6 +43,7 @@ class BooleanSelectorImpl implements BooleanSelector {
         : IntersectionSelector(this, other);
   }
 
+  @override
   BooleanSelector union(BooleanSelector other) {
     if (other == BooleanSelector.all) return other;
     if (other == BooleanSelector.none) return this;
@@ -48,14 +52,18 @@ class BooleanSelectorImpl implements BooleanSelector {
         : UnionSelector(this, other);
   }
 
-  void validate(bool isDefined(String variable)) {
+  @override
+  void validate(bool Function(String variable) isDefined) {
     _selector.accept(Validator(isDefined));
   }
 
+  @override
   String toString() => _selector.toString();
 
+  @override
   bool operator ==(other) =>
       other is BooleanSelectorImpl && _selector == other._selector;
 
+  @override
   int get hashCode => _selector.hashCode;
 }

lib/src/intersection_selector.dart

@@ -10,32 +10,40 @@ class IntersectionSelector implements BooleanSelector {
   final BooleanSelector _selector1;
   final BooleanSelector _selector2;
 
+  @override
   Iterable<String> get variables sync* {
     yield* _selector1.variables;
     yield* _selector2.variables;
   }
 
   IntersectionSelector(this._selector1, this._selector2);
 
+  @override
   bool evaluate(semantics) =>
       _selector1.evaluate(semantics) && _selector2.evaluate(semantics);
 
+  @override
   BooleanSelector intersection(BooleanSelector other) =>
       IntersectionSelector(this, other);
 
+  @override
   BooleanSelector union(BooleanSelector other) => UnionSelector(this, other);
 
-  void validate(bool isDefined(String variable)) {
+  @override
+  void validate(bool Function(String variable) isDefined) {
     _selector1.validate(isDefined);
     _selector2.validate(isDefined);
   }
 
-  String toString() => "($_selector1) && ($_selector2)";
+  @override
+  String toString() => '($_selector1) && ($_selector2)';
 
+  @override
   bool operator ==(other) =>
       other is IntersectionSelector &&
       _selector1 == other._selector1 &&
       _selector2 == other._selector2;
 
+  @override
   int get hashCode => _selector1.hashCode ^ _selector2.hashCode;
 }

lib/src/none.dart

@@ -8,17 +8,23 @@ import '../boolean_selector.dart';
 class None implements BooleanSelector {
   // TODO(nweiz): Stop explicitly providing a type argument when sdk#32412 is
   // fixed.
+  @override
   final variables = const <String>[];
 
   const None();
 
+  @override
   bool evaluate(semantics) => false;
 
+  @override
   BooleanSelector intersection(BooleanSelector other) => this;
 
+  @override
   BooleanSelector union(BooleanSelector other) => other;
 
-  void validate(bool isDefined(String variable)) {}
+  @override
+  void validate(bool Function(String) isDefined) {}
 
-  String toString() => "<none>";
+  @override
+  String toString() => '<none>';
 }

lib/src/parser.dart

@@ -28,7 +28,7 @@ class Parser {
 
     if (_scanner.peek().type != TokenType.endOfFile) {
       throw SourceSpanFormatException(
-          "Expected end of input.", _scanner.peek().span);
+          'Expected end of input.', _scanner.peek().span);
     }
 
     return selector;
@@ -97,7 +97,7 @@ class Parser {
         return VariableNode((token as IdentifierToken).name, token.span);
 
       default:
-        throw SourceSpanFormatException("Expected expression.", token.span);
+        throw SourceSpanFormatException('Expected expression.', token.span);
     }
   }
 }