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dart / dart_style / f8c285f3d1a13795588ce135833b2a75c957a9c0
commitf8c285f3d1a13795588ce135833b2a75c957a9c0[log] [tgz]
authorBob Nystrom <rnystrom@google.com>Mon May 20 10:48:56 2024 -0700
committerGitHub <noreply@github.com>Mon May 20 10:48:56 2024 -0700
tree3dc4a129b9cbe8c62f0fa7f8a08a864b074bffa5
parent0160142b3444e956936388010ac2bb1294dda8b9 [diff]
Remove some unnecessary Piece classes. (#1491)

Remove some unnecessary Piece classes.

In exploring various optimizations, it's clear that I'll probably need to make
some changes to how all of the Piece classes work. The more of those classes
there are, the harder that work is.

Fortunately, there are a few Piece classes that don't really need to exist. Most
were created before we had AdjacentPiece or the ability to insert spaces between
pieces.

This change:

* Removes ClausePiece which it turns out behaves exactly like InfixPiece (and
  then renames ClausesPiece to ClausePiece).

* Removes TryPiece. All it did was write its children with some spaces between
  them.

* Removes PostfixPiece. It was just like InfixPiece but without a first operand.
  But it's only used by imports, where we can use the import header as the first
  operand and just use InfixPiece.

* Remove AdjacentStringsPiece. It's just an InfixPiece that always splits.

* Get rid of CaseStatementPiece. Once you hoist out the optionality of the
  guard, it's just an InfixPiece.

* Reorganize ForPiece. Make that Piece just for the header part of a for
  statement or element. (We can almost get rid of this entirely and use
  AdjacentPiece, but it does some indentation that isn't otherwise supported.)
  
  Then to handle the body, we either write it inline if it's a block (the most
  common), or we use IfPiece, which has the same logic. Rename IfPiece to
  ControlFlowPiece to emphasize its more general use. It was already used for
  while statements, so this makes sense.
10 files changed
tree: 3dc4a129b9cbe8c62f0fa7f8a08a864b074bffa5
  1. .github/
  2. benchmark/
  3. bin/
  4. dist/
  5. example/
  6. lib/
  7. test/
  8. tool/
  9. .gitignore
  10. analysis_options.yaml
  11. AUTHORS
  12. CHANGELOG.md
  13. LICENSE
  14. pubspec.yaml
  15. README.md
README.md

The dart_style package defines an automatic, opinionated formatter for Dart code. It replaces the whitespace in your program with what it deems to be the best formatting for it. Resulting code should follow the Dart style guide but, moreso, should look nice to most human readers, most of the time.

The formatter handles indentation, inline whitespace, and (by far the most difficult) intelligent line wrapping. It has no problems with nested collections, function expressions, long argument lists, or otherwise tricky code.

The formatter turns code like this:

// BEFORE formatting
if (tag=='style'||tag=='script'&&(type==null||type == TYPE_JS
      ||type==TYPE_DART)||
  tag=='link'&&(rel=='stylesheet'||rel=='import')) {}

into:

// AFTER formatting
if (tag == 'style' ||
  tag == 'script' &&
      (type == null || type == TYPE_JS || type == TYPE_DART) ||
  tag == 'link' && (rel == 'stylesheet' || rel == 'import')) {}

The formatter will never break your code—you can safely invoke it automatically from build and presubmit scripts.

Style fixes

The formatter can also apply non-whitespace changes to make your code consistently idiomatic. You must opt into these by passing either --fix which applies all style fixes, or any of the --fix--prefixed flags to apply specific fixes.

For example, running with --fix-named-default-separator changes this:

greet(String name, {String title: "Captain"}) {
  print("Greetings, $title $name!");
}

into:

greet(String name, {String title = "Captain"}) {
  print("Greetings, $title $name!");
}

Using the formatter

The formatter is part of the unified dart developer tool included in the Dart SDK, so most users get it directly from there. That has the latest version of the formatter that was available when the SDK was released.

IDEs and editors that support Dart usually provide easy ways to run the formatter. For example, in WebStorm you can right-click a .dart file and then choose Reformat with Dart Style.

Here's a simple example of using the formatter on the command line:

$ dart format test.dart

This command formats the test.dart file and writes the result to the file.

dart format takes a list of paths, which can point to directories or files. If the path is a directory, it processes every .dart file in that directory or any of its subdirectories.

By default, it formats each file and write the formatting changes to the files. If you pass --output show, it prints the formatted code to stdout.

You may pass a -l option to control the width of the page that it wraps lines to fit within, but you're strongly encouraged to keep the default line length of 80 columns.

Validating files

If you want to use the formatter in something like a presubmit script or commit hook, you can pass flags to omit writing formatting changes to disk and to update the exit code to indicate success/failure:

$ dart format --output=none --set-exit-if-changed .

Running other versions of the formatter CLI command

If you need to run a different version of the formatter, you can globally activate the package from the dart_style package on pub.dev:

$ pub global activate dart_style
$ pub global run dart_style:format ...

Using the dart_style API

The package also exposes a single dart_style library containing a programmatic API for formatting code. Simple usage looks like this:

import 'package:dart_style/dart_style.dart';

main() {
  final formatter = DartFormatter();

  try {
    print(formatter.format("""
    library an_entire_compilation_unit;

    class SomeClass {}
    """));

    print(formatter.formatStatement("aSingle(statement);"));
  } on FormatterException catch (ex) {
    print(ex);
  }
}

Other resources

  • Before sending an email, see if you are asking a frequently asked question.

  • Before filing a bug, or if you want to understand how work on the formatter is managed, see how we track issues.