Format try statements. (#1332)

* Format try statements.

* Add try comment tests just in case.

* Use token's API to add spaces.

* Remove unnecessary override after rebase.

* Put the exception into a delimited list and everything else into an adjacentpiece.

* Remove unnecessary space.

lib/src/front_end/ast_node_visitor.dart

@@ -206,12 +206,12 @@ class AstNodeVisitor extends ThrowingAstVisitor<void>
 
   @override
   void visitCatchClause(CatchClause node) {
-    throw UnimplementedError();
+    assert(false, 'This node is handled by visitTryStatement().');
   }
 
   @override
   void visitCatchClauseParameter(CatchClauseParameter node) {
-    throw UnimplementedError();
+    token(node.name);
   }
 
   @override
@@ -1390,7 +1390,7 @@ class AstNodeVisitor extends ThrowingAstVisitor<void>
 
   @override
   void visitTryStatement(TryStatement node) {
-    throw UnimplementedError();
+    createTry(node);
   }
 
   @override

lib/src/front_end/piece_factory.dart

@@ -15,6 +15,7 @@ import '../piece/infix.dart';
 import '../piece/list.dart';
 import '../piece/piece.dart';
 import '../piece/postfix.dart';
+import '../piece/try.dart';
 import '../piece/type.dart';
 import 'ast_node_visitor.dart';
 import 'comment_writer.dart';
@@ -235,6 +236,92 @@ mixin PieceFactory implements CommentWriter {
     pieces.give(FunctionPiece(returnTypePiece, parametersPiece));
   }
 
+  /// Creates a [TryPiece] for try statement.
+  void createTry(TryStatement tryStatement) {
+    var piece = TryPiece();
+
+    token(tryStatement.tryKeyword);
+    var tryHeader = pieces.split();
+    createBlock(tryStatement.body);
+    var tryBlock = pieces.split();
+    piece.add(tryHeader, tryBlock);
+
+    for (var i = 0; i < tryStatement.catchClauses.length; i++) {
+      var catchClause = tryStatement.catchClauses[i];
+
+      Piece? onPiece;
+      if (catchClause.onKeyword case var onKeyword?) {
+        token(onKeyword, after: space);
+        visit(catchClause.exceptionType);
+        onPiece = pieces.split();
+      }
+
+      Piece? catchPiece;
+      if (catchClause.catchKeyword case var catchKeyword?) {
+        token(catchKeyword);
+        var catchKeywordPiece = pieces.split();
+
+        var builder = DelimitedListBuilder(this);
+        builder.leftBracket(catchClause.leftParenthesis!);
+        if (catchClause.exceptionParameter case var exceptionParameter?) {
+          builder.visit(exceptionParameter);
+        }
+        if (catchClause.stackTraceParameter case var stackTraceParameter?) {
+          builder.visit(stackTraceParameter);
+        }
+        builder.rightBracket(catchClause.rightParenthesis!);
+
+        catchPiece = AdjacentPiece(
+          [catchKeywordPiece, builder.build()],
+          spaceAfter: [catchKeywordPiece],
+        );
+      }
+
+      if (onPiece != null && catchPiece != null) {
+        pieces.give(AdjacentPiece(
+          [onPiece, catchPiece],
+          spaceAfter: [onPiece],
+        ));
+      } else if (onPiece != null) {
+        pieces.give(onPiece);
+      } else if (catchPiece != null) {
+        pieces.give(catchPiece);
+      }
+      var catchClauseHeader = pieces.split();
+
+      // Edge case: When there's another catch/on/finally after this one, we
+      // want to force the block to split even if it's empty.
+      //
+      // ```
+      // try {
+      //   ..
+      // } on Foo {
+      // } finally Bar {
+      //   body;
+      // }
+      // ```
+      var forceSplit = i < tryStatement.catchClauses.length - 1 ||
+          tryStatement.finallyBlock != null;
+      createBlock(
+        catchClause.body,
+        forceSplit: forceSplit,
+      );
+      var catchClauseBody = pieces.split();
+
+      piece.add(catchClauseHeader, catchClauseBody);
+    }
+
+    if (tryStatement.finallyBlock case var finallyBlock?) {
+      token(tryStatement.finallyKeyword);
+      var finallyHeader = pieces.split();
+      createBlock(finallyBlock);
+      var finallyBody = pieces.split();
+      piece.add(finallyHeader, finallyBody);
+    }
+
+    pieces.give(piece);
+  }
+
   // TODO(tall): Generalize this to work with if elements too.
   /// Creates a piece for a chain of if-else-if... statements.
   void createIf(IfStatement ifStatement) {

lib/src/piece/adjacent.dart

@@ -8,12 +8,17 @@ import 'piece.dart';
 class AdjacentPiece extends Piece {
   final List<Piece> _pieces;
 
-  AdjacentPiece(this._pieces);
+  /// The pieces that should have a space after them.
+  final Set<Piece> _spaceAfter;
+
+  AdjacentPiece(this._pieces, {List<Piece> spaceAfter = const []})
+      : _spaceAfter = spaceAfter.toSet();
 
   @override
   void format(CodeWriter writer, State state) {
     for (var piece in _pieces) {
       writer.format(piece);
+      if (_spaceAfter.contains(piece)) writer.space();
     }
   }
 

lib/src/piece/try.dart

@@ -0,0 +1,48 @@
+// 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 'piece.dart';
+
+/// A piece for a try statement.
+class TryPiece extends Piece {
+  final List<_TrySectionPiece> _sections = [];
+
+  void add(Piece header, Piece block) {
+    _sections.add(_TrySectionPiece(header, block));
+  }
+
+  @override
+  void format(CodeWriter writer, State state) {
+    for (var i = 0; i < _sections.length; i++) {
+      var section = _sections[i];
+      writer.format(section.header);
+      writer.space();
+      writer.format(section.body);
+
+      // Adds the space between the end of a block and the next header.
+      if (i < _sections.length - 1) {
+        writer.space();
+      }
+    }
+  }
+
+  @override
+  void forEachChild(void Function(Piece piece) callback) {
+    for (var section in _sections) {
+      callback(section.header);
+      callback(section.body);
+    }
+  }
+}
+
+/// A section for a try.
+///
+/// This could be a try, an on/catch, or a finally section. They are all
+/// formatted similarly.
+class _TrySectionPiece {
+  final Piece header;
+  final Piece body;
+
+  _TrySectionPiece(this.header, this.body);
+}

test/statement/try.stmt

@@ -0,0 +1,113 @@
+40 columns                              |
+>>> Try and catch exception.
+try {
+doSomething();
+} catch (e) {
+print(e);
+}
+<<<
+try {
+  doSomething();
+} catch (e) {
+  print(e);
+}
+>>> Try and catch exception with on clause.
+try{
+doSomething();
+}on Exception catch (e){
+print(e);
+}
+<<<
+try {
+  doSomething();
+} on Exception catch (e) {
+  print(e);
+}
+>>> Try and catch exception with on clause and stack trace.
+try{
+doSomething();
+}on Exception catch (e,   s){
+print(e);
+}
+<<<
+try {
+  doSomething();
+} on Exception catch (e, s) {
+  print(e);
+}
+>>> Split empty catch if there is a finally.
+try {;} catch (err) {} finally {;}
+<<<
+try {
+  ;
+} catch (err) {
+} finally {
+  ;
+}
+>>> Split empty on if there is a finally.
+try {;} on Exception {} finally {;}
+<<<
+try {
+  ;
+} on Exception {
+} finally {
+  ;
+}
+>>> Split all empty catches if there is a finally.
+try {;} catch (err1) {} catch (err2) {} catch (err3) {} finally {;}
+<<<
+try {
+  ;
+} catch (err1) {
+} catch (err2) {
+} catch (err3) {
+} finally {
+  ;
+}
+>>> Split leading empty catches if there are multiple.
+try {;} catch (err1) {} catch (err2) {} catch (err3) {}
+<<<
+try {
+  ;
+} catch (err1) {
+} catch (err2) {
+} catch (err3) {}
+>>> Split empty catch with on clause if there is a finally.
+try {
+  doSomething();
+} on Exception catch (e) {} finally {
+  cleanupSomething();
+}
+<<<
+try {
+  doSomething();
+} on Exception catch (e) {
+} finally {
+  cleanupSomething();
+}
+>>> Split multiple on clauses.
+try {
+  doSomething();
+} on FooException {} on BarException {
+  doSomething();
+}
+<<<
+try {
+  doSomething();
+} on FooException {
+} on BarException {
+  doSomething();
+}
+>>> Don't split try.
+try {
+  doSomething();
+} on FooException {} on BarException {
+  doSomething();
+}
+<<<
+try {
+  doSomething();
+} on FooException {
+} on BarException {
+  doSomething();
+}