Allow command-line API to pass in selection to preserve. Fix #194.

bin/format.dart

 // Copyright (c) 2015, 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 'dart:convert';
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:dart_style/src/dart_formatter.dart';
 import 'package:dart_style/src/formatter_exception.dart';
 import 'package:dart_style/src/formatter_options.dart';
 import 'package:dart_style/src/io.dart';
+import 'package:dart_style/src/source_code.dart';
 
 void main(List<String> args) {
   var parser = new ArgParser(allowTrailingOptions: true);
 
   parser.addFlag("help", abbr: "h", negatable: false,
       help: "Shows usage information.");
   parser.addOption("line-length", abbr: "l",
       help: "Wrap lines longer than this.",
       defaultsTo: "80");
+  parser.addOption("preserve",
+      help: 'Selection to preserve, formatted as "start:length".');
   parser.addFlag("dry-run", abbr: "n", negatable: false,
       help: "Show which files would be modified but make no changes.");
   parser.addFlag("overwrite", abbr: "w", negatable: false,
       help: "Overwrite input files with formatted output.");
   parser.addFlag("machine", abbr: "m", negatable: false,
       help: "Produce machine-readable JSON output.");
   parser.addFlag("follow-links", negatable: false,
       help: "Follow links to files and directories.\n"
             "If unset, links will be ignored.");
   parser.addFlag("transform", abbr: "t", negatable: false,
       help: "Unused flag for compability with the old formatter.");
 
   var argResults;
   try {
     argResults = parser.parse(args);
   } on FormatException catch (err) {
-    printUsage(parser, err.message);
-    exitCode = 64;
-    return;
+    usageError(parser, err.message);
   }
 
   if (argResults["help"]) {
     printUsage(parser);
     return;
   }
 
+  // Can only preserve a selection when parsing from stdin.
+  var selection;
+
+  if (argResults["preserve"] != null && argResults.rest.isNotEmpty) {
+    usageError(parser, "Can only use --preserve when reading from stdin.");
+  }
+
+  try {
+    selection = parseSelection(argResults["preserve"]);
+  } on FormatException catch (_) {
+    usageError(parser,
+        '--preserve must be a colon-separated pair of integers, was '
+        '"${argResults['preserve']}".');
+  }
+
   if (argResults["dry-run"] && argResults["overwrite"]) {
-    printUsage(parser,
+    usageError(parser,
         "Cannot use --dry-run and --overwrite at the same time.");
-    exitCode = 64;
-    return;
   }
 
   checkForReporterCollision(String chosen, String other) {
-    if (!argResults[other]) return false;
+    if (!argResults[other]) return;
 
-    printUsage(parser,
+    usageError(parser,
         "Cannot use --$chosen and --$other at the same time.");
-    exitCode = 64;
-    return true;
   }
 
   var reporter = OutputReporter.print;
   if (argResults["dry-run"]) {
-    if (checkForReporterCollision("dry-run", "overwrite")) return;
-    if (checkForReporterCollision("dry-run", "machine")) return;
+    checkForReporterCollision("dry-run", "overwrite");
+    checkForReporterCollision("dry-run", "machine");
 
     reporter = OutputReporter.dryRun;
   } else if (argResults["overwrite"]) {
-    if (checkForReporterCollision("overwrite", "machine")) return;
+    checkForReporterCollision("overwrite", "machine");
 
     if (argResults.rest.isEmpty) {
-      printUsage(parser,
+      usageError(parser,
           "Cannot use --overwrite without providing any paths to format.");
-      exitCode = 64;
-      return;
     }
 
     reporter = OutputReporter.overwrite;
   } else if (argResults["machine"]) {
     reporter = OutputReporter.printJson;
   }
 
   var pageWidth;
 
   try {
     pageWidth = int.parse(argResults["line-length"]);
   } on FormatException catch (_) {
-    printUsage(parser, '--line-length must be an integer, was '
+    usageError(parser, '--line-length must be an integer, was '
                        '"${argResults['line-length']}".');
-    exitCode = 64;
-    return;
   }
 
   var followLinks = argResults["follow-links"];
 
   var options = new FormatterOptions(reporter,
       pageWidth: pageWidth, followLinks: followLinks);
 
   if (argResults.rest.isEmpty) {
-    formatStdin(options);
+    formatStdin(options, selection);
   } else {
     formatPaths(options, argResults.rest);
   }
 }
 
+List<int> parseSelection(String selection) {
+  if (selection == null) return null;
+
+  var coordinates = selection.split(":");
+  if (coordinates.length != 2) {
+    throw new FormatException(
+        'Selection should be a colon-separated pair of integers, "123:45".');
+  }
+
+  return coordinates.map((coord) => coord.trim()).map(int.parse).toList();
+}
+
 /// Reads input from stdin until it's closed, and the formats it.
-void formatStdin(FormatterOptions options) {
+void formatStdin(FormatterOptions options, List<int> selection) {
+  var selectionStart = 0;
+  var selectionLength = 0;
+
+  if (selection != null) {
+    selectionStart = selection[0];
+    selectionLength = selection[1];
+  }
+
   var input = new StringBuffer();
   stdin.transform(new Utf8Decoder()).listen(input.write, onDone: () {
     var formatter = new DartFormatter(pageWidth: options.pageWidth);
     try {
-      var source = input.toString();
-      var output = formatter.format(source, uri: "stdin");
+      var source = new SourceCode(input.toString(),
+          uri: "stdin",
+          selectionStart: selectionStart,
+          selectionLength: selectionLength);
+      var output = formatter.formatSource(source);
       options.reporter.showFile(null, "<stdin>", output,
           changed: source != output);
       return true;
     } on FormatterException catch (err) {
       stderr.writeln(err.message());
     } catch (err, stack) {
       stderr.writeln('''Hit a bug in the formatter when formatting stdin.
 Please report at: github.com/dart-lang/dart_style/issues
 $err
 $stack''');
@@ skipping 16 matching lines @@
     if (file.existsSync()) {
       if (!processFile(options, file)) {
         exitCode = 65;
       }
     } else {
       stderr.writeln('No file or directory found at "$path".');
     }
   }
 }
 
+/// Prints [error] and usage help then exits with exit code 64.
+void usageError(ArgParser parser, String error) {
+  printUsage(parser, error);
+  exit(64);
+}
+
 void printUsage(ArgParser parser, [String error]) {
   var output = stdout;
 
   var message = "Reformats whitespace in Dart source files.";
   if (error != null) {
     message = error;
     output = stdout;
   }
 
   output.write("""$message
 
 Usage: dartfmt [-n|-w] [files or directories...]
 
 ${parser.usage}
 """);
 }