analyzer: Document DisplayStringBuilder and clean up fields.

* `skipAllDynamicArguments` was always false; remove.
* `withNullability` and `multiline` are both unused outside the class;
  make them private.

Change-Id: Ic869abc1f76d0cc59e9feaffe969a24ea1deb363
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/335360
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Kallen Tu <[email protected]>

pkg/analyzer/lib/src/dart/element/display_string_builder.dart

@@ -11,18 +11,21 @@ import 'package:analyzer/src/dart/element/type_algebra.dart';
 import 'package:analyzer/src/dart/resolver/variance.dart';
 import 'package:analyzer/src/generated/element_type_provider.dart';
 
+/// A class that builds a "display string" for [Element]s and [DartType]s.
 class ElementDisplayStringBuilder {
   final StringBuffer _buffer = StringBuffer();
 
-  final bool skipAllDynamicArguments;
-  final bool withNullability;
-  final bool multiline;
+  /// Whether to include the nullability ('?' characters) in a display string.
+  final bool _withNullability;
+
+  /// Whether to allow a display string to be written in multiple lines.
+  final bool _multiline;
 
   ElementDisplayStringBuilder({
-    required this.skipAllDynamicArguments,
-    required this.withNullability,
-    this.multiline = false,
-  });
+    required bool withNullability,
+    bool multiline = false,
+  })  : _withNullability = withNullability,
+        _multiline = multiline;
 
   @override
   String toString() {
@@ -336,7 +339,7 @@ class ElementDisplayStringBuilder {
     // Assume the display string looks better wrapped when there are at least
     // three parameters. This avoids having to pre-compute the single-line
     // version and know the length of the function name/return type.
-    var multiline = allowMultiline && this.multiline && parameters.length >= 3;
+    var multiline = allowMultiline && _multiline && parameters.length >= 3;
 
     // The prefix for open groups is included in separator for single-line but
     // not for multline so must be added explicitly.
@@ -388,16 +391,13 @@ class ElementDisplayStringBuilder {
   }
 
   void _writeNullability(NullabilitySuffix nullabilitySuffix) {
-    if (withNullability) {
+    if (_withNullability) {
       switch (nullabilitySuffix) {
         case NullabilitySuffix.question:
           _write('?');
-          break;
         case NullabilitySuffix.star:
           _write('*');
-          break;
         case NullabilitySuffix.none:
-          break;
       }
     }
   }
@@ -411,12 +411,6 @@ class ElementDisplayStringBuilder {
       return;
     }
 
-    if (skipAllDynamicArguments) {
-      if (typeArguments.every((t) => t is DynamicType)) {
-        return;
-      }
-    }
-
     _write('<');
     for (var i = 0; i < typeArguments.length; i++) {
       if (i != 0) {

pkg/analyzer/lib/src/dart/element/element.dart

@@ -2469,7 +2469,6 @@ abstract class ElementImpl implements Element {
     bool multiline = false,
   }) {
     var builder = ElementDisplayStringBuilder(
-      skipAllDynamicArguments: false,
       withNullability: withNullability,
       multiline: multiline,
     );

pkg/analyzer/lib/src/dart/element/member.dart

@@ -683,7 +683,6 @@ abstract class Member implements Element {
     bool multiline = false,
   }) {
     var builder = ElementDisplayStringBuilder(
-      skipAllDynamicArguments: false,
       withNullability: withNullability,
       multiline: multiline,
     );

pkg/analyzer/lib/src/dart/element/type.dart

@@ -1347,11 +1347,9 @@ abstract class TypeImpl implements DartType {
 
   @override
   String getDisplayString({
-    bool skipAllDynamicArguments = false,
     required bool withNullability,
   }) {
     var builder = ElementDisplayStringBuilder(
-      skipAllDynamicArguments: skipAllDynamicArguments,
       withNullability: withNullability,
     );
     appendTo(builder);