Smarter splitting around named collection arguments.

lib/src/rule/argument.dart

Index: lib/src/rule/argument.dart
diff --git a/lib/src/rule/argument.dart b/lib/src/rule/argument.dart
index 046ff10ca27f6ee55300c037063719f50541d79a..ed7758a3e216377e42a5c02dc7bb417a19bf33a8 100644
--- a/lib/src/rule/argument.dart
+++ b/lib/src/rule/argument.dart
@@ -9,6 +9,24 @@ import 'rule.dart';
 
 /// Base class for a rule that handles argument or parameter lists.
 abstract class ArgumentRule extends Rule {
+  /// The chunks prior to each positional argument.
+  final List<Chunk> _arguments = [];
+
+  /// The rule used to split collections in the argument list, if any.
+  Rule _collectionRule;
+
+  /// The number of leading collection arguments.
+  ///
+  /// This and [_trailingCollections] cannot both be positive. If every
+  /// argument is a collection, this will be [_arguments.length] and
+  /// [_trailingCollections] will be 0.
+  final int _leadingCollections;
+
+  /// The number of trailing collections.
+  ///
+  /// This and [_leadingCollections] cannot both be positive.
+  final int _trailingCollections;
+
   /// If true, then inner rules that are written will force this rule to split.
   ///
   /// Temporarily disabled while writing collectio arguments so that they can be
@@ -18,6 +36,27 @@ abstract class ArgumentRule extends Rule {
   /// Don't split when an inner collection rule splits.
   bool get splitsOnInnerRules => _trackInnerRules;
 
+  ArgumentRule(this._collectionRule, this._leadingCollections,
+      this._trailingCollections);
+
+  void addConstrainedRules(Set<Rule> rules) {
+    super.addConstrainedRules(rules);
+    if (_collectionRule != null) rules.add(_collectionRule);
+  }
+
+  void forgetUnusedRules() {
+    super.forgetUnusedRules();
+    if (_collectionRule != null && _collectionRule.index == null) {
+      _collectionRule = null;
+    }
+  }
+
+  /// Remembers [chunk] as containing the split that occurs right before an
+  /// argument in the list.
+  void beforeArgument(Chunk chunk) {
+    _arguments.add(chunk);
+  }
+
   /// Called before a collection argument is written.
   ///
   /// Disables tracking inner rules while a collection argument is written.
@@ -37,12 +76,6 @@ abstract class ArgumentRule extends Rule {
 
 /// Base class for a rule for handling positional argument lists.
 abstract class PositionalRule extends ArgumentRule {
-  /// The chunks prior to each positional argument.
-  final List<Chunk> _arguments = [];
-
-  /// The rule used to split collections in the argument list, if any.
-  Rule _collectionRule;
-
   /// If there are named arguments following these positional ones, this will
   /// be their rule.
   Rule _namedArgsRule;
@@ -51,10 +84,12 @@ abstract class PositionalRule extends ArgumentRule {
   ///
   /// If [_collectionRule] is given, it is the rule used to split the collection
   /// arguments in the list.
-  PositionalRule(this._collectionRule);
+  PositionalRule(
+      Rule collectionRule, int leadingCollections, int trailingCollections)
+      : super(collectionRule, leadingCollections, trailingCollections);
 
   void addConstrainedRules(Set<Rule> rules) {
-    if (_collectionRule != null) rules.add(_collectionRule);
+    super.addConstrainedRules(rules);
     if (_namedArgsRule != null) rules.add(_namedArgsRule);
   }
 
@@ -63,21 +98,15 @@ abstract class PositionalRule extends ArgumentRule {
     if (_namedArgsRule != null && _namedArgsRule.index == null) {
       _namedArgsRule = null;
     }
-
-    if (_collectionRule != null && _collectionRule.index == null) {
-      _collectionRule = null;
-    }
-  }
-
-  /// Remembers [chunk] as containing the split that occurs right before an
-  /// argument in the list.
-  void beforeArgument(Chunk chunk) {
-    _arguments.add(chunk);
   }
 
-  /// Remembers that [rule] is the [NamedArgsRule] immediately following this
+  /// Remembers that [rule] is the [Rule] immediately following this positional
   /// positional argument list.
-  void setNamedArgsRule(NamedRule rule) {
+  ///
+  /// This is normally a [NamedRule] but [PositionalRule] is also used for the
+  /// property accesses at the beginning of a call chain, in which case this
+  /// is just a [SimpleRule].
+  void setNamedArgsRule(Rule rule) {
     _namedArgsRule = rule;
   }
 
@@ -120,7 +149,7 @@ class SinglePositionalRule extends PositionalRule {
   /// collections in the list. If [splitsOnInnerRules] is `true`, then we will
   /// split before the argument if the argument itself contains a split.
   SinglePositionalRule(Rule collectionRule, {bool splitsOnInnerRules})
-      : super(collectionRule),
+      : super(collectionRule, 0, 0),
         splitsOnInnerRules =
             splitsOnInnerRules != null ? splitsOnInnerRules : false;
 
@@ -158,18 +187,6 @@ class SinglePositionalRule extends PositionalRule {
 /// splits before all of the non-collection arguments, but does not split
 /// before the collections, so that they can split internally.
 class MultiplePositionalRule extends PositionalRule {
-  /// The number of leading collection arguments.
-  ///
-  /// This and [_trailingCollections] cannot both be positive. If every
-  /// argument is a collection, this will be [_arguments.length] and
-  /// [_trailingCollections] will be 0.
-  final int _leadingCollections;
-
-  /// The number of trailing collections.
-  ///
-  /// This and [_leadingCollections] cannot both be positive.
-  final int _trailingCollections;
-
   int get numValues {
     // Can split before any one argument, none, or all.
     var result = 2 + _arguments.length;
@@ -187,8 +204,8 @@ class MultiplePositionalRule extends PositionalRule {
   }
 
   MultiplePositionalRule(
-      Rule collectionRule, this._leadingCollections, this._trailingCollections)
-      : super(collectionRule);
+      Rule collectionRule, int leadingCollections, int trailingCollections)
+      : super(collectionRule, leadingCollections, trailingCollections);
 
   String toString() => "*Pos${super.toString()}";
 
@@ -273,33 +290,46 @@ class MultiplePositionalRule extends PositionalRule {
 
 /// Splitting rule for a list of named arguments or parameters. Its values mean:
 ///
-/// * 0: Do not split at all.
-/// * 1: Split only before first argument.
-/// * 2: Split before all arguments, including the first.
+/// * Do not split at all.
+/// * Split only before first argument.
+/// * Split before all arguments.
 class NamedRule extends ArgumentRule {
-  /// The chunk prior to the first named argument.
-  Chunk _first;
-
-  /// Whether any of the named arguments are collection literals.
-  final bool _containsCollections;
-
   int get numValues => 3;
 
-  NamedRule({bool containsCollections})
-      : _containsCollections = containsCollections ?? false;
-
-  void beforeArguments(Chunk chunk) {
-    assert(_first == null);
-    _first = chunk;
-  }
+  NamedRule(
+      Rule collectionRule, int leadingCollections, int trailingCollections)
+      : super(collectionRule, leadingCollections, trailingCollections);
 
   bool isSplitAtValue(int value, Chunk chunk) {
-    // Only split before the first argument.
-    if (value == 1) return chunk == _first;
+    // Move all arguments to the second line as a unit.
+    if (value == 1) return chunk == _arguments.first;
 
-    // Split before every argument.
+    // Otherwise, split before all arguments.
     return true;
   }
 
+  int constrain(int value, Rule other) {
+    var constrained = super.constrain(value, other);
+    if (constrained != null) return constrained;
+
+    // Decide how to constrain the collection rule.
+    if (other != _collectionRule) return null;
+
+    // If all of the collections are in the named arguments, [_collectionRule]
+    // will not be null, but we don't have to handle it.
+    if (_leadingCollections == 0 && _trailingCollections == 0) return null;
+
+    // If we aren't splitting any args, we can split the collection.
+    if (value == Rule.unsplit) return null;
+
+    // Split only before the first argument. Don't allow the collections to
+    // split.
+    if (value == 1) return Rule.unsplit;
+
+    // Split before all of the arguments, even the collections. We'll allow
+    // them to split but indent their bodies if they do.
+    return null;
+  }
+
   String toString() => "Named${super.toString()}";
 }