commit | d50165dc7da745160c8679bbdd81e6c21a4faa3d | [log] [tgz] |
---|---|---|
author | Bob Nystrom <rnystrom@google.com> | Mon Jan 29 10:33:03 2024 -0800 |
committer | GitHub <noreply@github.com> | Mon Jan 29 10:33:03 2024 -0800 |
tree | 90eebab1ad2b000e92aa128eb7ec73e3f5f62441 | |
parent | 15f032a31548802426dc829f5ecf471a0aa98adb [diff] |
Fix bug where solver looks at the last piece on line instead of first. (#1367) The Solver selects states for all pieces in the piece tree to decide how to format. It does so by exploring a tree of incremental solutions where each set of states is a node in the tree and branches are formed by incrementally binding new states. Exploring the full tree is massively slow. A key optimization is that the solver only looks at changing the state of pieces on lines that actually overflow or are invalid. That way pieces on lines that fit and don't need to split are ignored. It goes further: it only looks at the *first* piece on the *first* line that overflows. Any pieces following that one may be affected by how changing the state of the preceding piece changes the formatting, so we ignore those. At least, that's the intent. It turns out there's actually a bug and the solver looks at the *last* piece on the *first* overflowing line. That can lead to subtly different formatting when there are multiple splittable pieces on the same line. In practice, only one extremely weird test was affected. I suspect that if we started running the formatter on larger code samples, we'd find other more obvious mistakes. This fixes that.
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.
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!"); }
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.
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 .
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 ...
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); } }
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.