Format configurations in imports and exports. (#1265)

Format configurations in imports and exports.

This also brings in InfixPiece which will be used for other infix
operators and infix-like constructs.

lib/src/front_end/ast_node_visitor.dart

@@ -188,7 +188,19 @@ class AstNodeVisitor extends ThrowingAstVisitor<void> with PieceFactory {
 
   @override
   void visitConfiguration(Configuration node) {
-    throw UnimplementedError();
+    token(node.ifKeyword);
+    writer.space();
+    token(node.leftParenthesis);
+
+    if (node.equalToken case var equals?) {
+      createInfix(node.name, equals, node.value!, hanging: true);
+    } else {
+      visit(node.name);
+    }
+
+    token(node.rightParenthesis);
+    writer.space();
+    visit(node.uri);
   }
 
   @override
@@ -238,7 +250,7 @@ class AstNodeVisitor extends ThrowingAstVisitor<void> with PieceFactory {
 
   @override
   void visitDottedName(DottedName node) {
-    throw UnimplementedError();
+    createDotted(node.components);
   }
 
   @override
@@ -268,9 +280,6 @@ class AstNodeVisitor extends ThrowingAstVisitor<void> with PieceFactory {
 
   @override
   void visitExportDirective(ExportDirective node) {
-    // TODO(tall): Format configurations.
-    if (node.configurations.isNotEmpty) throw UnimplementedError();
-
     createImport(node, node.exportKeyword);
   }
 
@@ -416,9 +425,6 @@ class AstNodeVisitor extends ThrowingAstVisitor<void> with PieceFactory {
 
   @override
   void visitImportDirective(ImportDirective node) {
-    // TODO(tall): Format configurations.
-    if (node.configurations.isNotEmpty) throw UnimplementedError();
-
     createImport(node, node.importKeyword,
         deferredKeyword: node.deferredKeyword,
         asKeyword: node.asKeyword,

lib/src/front_end/piece_factory.dart

@@ -5,6 +5,7 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 
 import '../piece/import.dart';
+import '../piece/infix.dart';
 import '../piece/piece.dart';
 import '../piece/postfix.dart';
 import '../piece/sequence.dart';
@@ -72,6 +73,18 @@ mixin PieceFactory {
     visit(directive.uri);
     var directivePiece = writer.pop();
 
+    Piece? configurationsPiece;
+    if (directive.configurations.isNotEmpty) {
+      var configurations = <Piece>[];
+      for (var configuration in directive.configurations) {
+        writer.split();
+        visit(configuration);
+        configurations.add(writer.pop());
+      }
+
+      configurationsPiece = PostfixPiece(configurations);
+    }
+
     Piece? asClause;
     if (asKeyword != null) {
       writer.split();
@@ -112,7 +125,34 @@ mixin PieceFactory {
 
     token(directive.semicolon);
 
-    writer.push(ImportPiece(directivePiece, asClause, combinator));
+    writer.push(
+        ImportPiece(directivePiece, configurationsPiece, asClause, combinator));
+  }
+
+  /// Creates a single infix operation.
+  ///
+  /// If [hanging] is `true` then the operator goes at the end of the first
+  /// line, like `+`. Otherwise, it goes at the beginning of the second, like
+  /// `as`.
+  void createInfix(AstNode left, Token operator, AstNode right,
+      {bool hanging = false}) {
+    var operands = <Piece>[];
+    visit(left);
+    operands.add(writer.pop());
+
+    if (hanging) {
+      writer.space();
+      token(operator);
+      writer.split();
+    } else {
+      writer.split();
+      token(operator);
+      writer.space();
+    }
+
+    visit(right);
+    operands.add(writer.pop());
+    writer.push(InfixPiece(operands));
   }
 
   /// Emit [token], along with any comments and formatted whitespace that comes

lib/src/piece/import.dart

@@ -12,9 +12,12 @@ import 'piece.dart';
 /// imports, the configurations (`if` clauses), and combinators (`show` and
 /// `hide`).
 class ImportPiece extends Piece {
-  /// The directive keyword and its URI.
+  /// The main directive and its URI.
   final Piece directive;
 
+  /// If the directive has `if` configurations, this is them.
+  final Piece? configurations;
+
   /// The `as` clause for this directive.
   ///
   /// Null if this is not an import or it has no library prefix.
@@ -23,21 +26,24 @@ class ImportPiece extends Piece {
   /// The piece for the `show` and/or `hide` combinators.
   final Piece? combinator;
 
-  ImportPiece(this.directive, this.asClause, this.combinator);
+  ImportPiece(
+      this.directive, this.configurations, this.asClause, this.combinator);
 
   @override
   int get stateCount => 1;
 
   @override
   void format(CodeWriter writer, int state) {
     writer.format(directive);
+    writer.formatOptional(configurations);
     writer.formatOptional(asClause);
     writer.formatOptional(combinator);
   }
 
   @override
   void forEachChild(void Function(Piece piece) callback) {
     callback(directive);
+    if (configurations case var configurations?) callback(configurations);
     if (asClause case var asClause?) callback(asClause);
     if (combinator case var combinator?) callback(combinator);
   }

lib/src/piece/infix.dart

@@ -0,0 +1,54 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import '../back_end/code_writer.dart';
+import '../constants.dart';
+import 'piece.dart';
+
+/// A piece for a series of binary expressions at the same precedence, like:
+///
+/// ```
+/// a + b + c
+/// ```
+class InfixPiece extends Piece {
+  /// The series of operands.
+  ///
+  /// Since we don't split on both sides of the operator, the operators will be
+  /// embedded in the operand pieces. If the operator is a hanging one, it will
+  /// be in the preceding operand, so `1 + 2` becomes "Infix(`1 +`, `2`)".
+  /// A leading operator like `foo as int` becomes "Infix(`foo`, `as int`)".
+  final List<Piece> operands;
+
+  InfixPiece(this.operands);
+
+  @override
+  int get stateCount => 2;
+
+  @override
+  void format(CodeWriter writer, int state) {
+    switch (state) {
+      case 0:
+        writer.setAllowNewlines(false);
+        for (var i = 0; i < operands.length; i++) {
+          writer.format(operands[i]);
+
+          if (i < operands.length - 1) writer.space();
+        }
+
+      case 1:
+        writer.setNesting(Indent.expression);
+        for (var i = 0; i < operands.length; i++) {
+          writer.format(operands[i]);
+          if (i < operands.length - 1) writer.newline();
+        }
+    }
+  }
+
+  @override
+  void forEachChild(void Function(Piece piece) callback) {
+    operands.forEach(callback);
+  }
+
+  @override
+  String toString() => 'Infix';
+}

test/top_level/export.unit

@@ -8,4 +8,9 @@ export 'package:some/very/long/export/path.dart';
 ### here to make sure that export directives handle the combinators.
 export 'a.dart'show Ape,Bear hide Cat;
 <<<
-export 'a.dart' show Ape, Bear hide Cat;
+export 'a.dart' show Ape, Bear hide Cat;
+>>> Configuration.
+### More detailed configuration tests are handled under import.
+export'a'if(b  . c=='d'   )'e';
+<<<
+export 'a' if (b.c == 'd') 'e';

test/top_level/import.unit

@@ -27,4 +27,38 @@ import 'package:foo/foo.dart'
 import 'package:foo/some/path/foo.dart' deferred as very_long_identifier_path;
 <<<
 import 'package:foo/some/path/foo.dart'
-    deferred as very_long_identifier_path;
+    deferred as very_long_identifier_path;
+>>> Dotted identifier in configuration.
+import'a'if(b  . c . d)'e';
+<<<
+import 'a' if (b.c.d) 'e';
+>>> Multiple configurations on one line.
+import 'a' if (b) 'b' if (c) 'c';
+<<<
+import 'a' if (b) 'b' if (c) 'c';
+>>> If configurations don't fit, they all split.
+import 'long/import/url.dart' if (b) 'b' if (c) 'c';
+<<<
+import 'long/import/url.dart'
+    if (b) 'b'
+    if (c) 'c';
+>>> Configurations don't split before URI.
+import 'long/import/url.dart' if (config) 'very/long/configured/import/url.dart';
+<<<
+import 'long/import/url.dart'
+    if (config) 'very/long/configured/import/url.dart';
+>>> Unsplit configuration with `==`.
+import 'a.dart' if (b == 's') 'c';
+<<<
+import 'a.dart' if (b == 's') 'c';
+>>> Split before `if` before `==`.
+import 'some/uri.dart' if (debug == 'string') 'c';
+<<<
+import 'some/uri.dart'
+    if (debug == 'string') 'c';
+>>> Split before `==` in configuration.
+import 'some/uri.dart' if (config.name.debug == 'string') 'c';
+<<<
+import 'some/uri.dart'
+    if (config.name.debug ==
+        'string') 'c';