blob: e926859fafdb78e8d410c6db2fa80f6e9f5e04b9 [file] [log] [blame]
// Copyright (c) 2014, 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.
library dart_style.src.chunk_builder;
import 'chunk.dart';
import 'dart_formatter.dart';
import 'debug.dart' as debug;
import 'line_writer.dart';
import 'nesting_level.dart';
import 'nesting_builder.dart';
import 'rule/rule.dart';
import 'source_code.dart';
import 'whitespace.dart';
/// Matches if the last character of a string is an identifier character.
final _trailingIdentifierChar = new RegExp(r"[a-zA-Z0-9_]$");
/// Takes the incremental serialized output of [SourceVisitor]--the source text
/// along with any comments and preserved whitespace--and produces a coherent
/// tree of [Chunk]s which can then be split into physical lines.
/// Keeps track of leading indentation, expression nesting, and all of the hairy
/// code required to seamlessly integrate existing comments into the pure
/// output produced by [SourceVisitor].
class ChunkBuilder {
final DartFormatter _formatter;
/// The builder for the code surrounding the block that this writer is for, or
/// `null` if this is writing the top-level code.
final ChunkBuilder _parent;
final SourceCode _source;
final List<Chunk> _chunks;
/// The whitespace that should be written to [_chunks] before the next
/// non-whitespace token.
/// This ensures that changes to indentation and nesting also apply to the
/// most recent split, even if the visitor "creates" the split before changing
/// indentation or nesting.
Whitespace _pendingWhitespace = Whitespace.none;
/// The nested stack of rules that are currently in use.
/// New chunks are implicitly split by the innermost rule when the chunk is
/// ended.
final _rules = <Rule>[];
/// The set of rules known to contain hard splits that will in turn force
/// these rules to harden.
/// This is accumulated lazily while chunks are being built. Then, once they
/// are all done, the rules are all hardened. We do this later because some
/// rules may not have all of their constraints fully wired up until after
/// the hard split appears. For example, a hard split in a positional
/// argument list needs to force the named arguments to split too, but we
/// don't create that rule until after the positional arguments are done.
final _hardSplitRules = new Set<Rule>();
/// The list of rules that are waiting until the next whitespace has been
/// written before they start.
final _lazyRules = <Rule>[];
/// The nested stack of spans that are currently being written.
final _openSpans = <OpenSpan>[];
/// The current state.
final _nesting = new NestingBuilder();
/// The stack of nesting levels where block arguments may start.
/// A block argument's contents will nest at the last level in this stack.
final _blockArgumentNesting = <NestingLevel>[];
/// The index of the "current" chunk being written.
/// If the last chunk is still being appended to, this is its index.
/// Otherwise, it is the index of the next chunk which will be created.
int get _currentChunkIndex {
if (_chunks.isEmpty) return 0;
if (_chunks.last.canAddText) return _chunks.length - 1;
return _chunks.length;
/// Whether or not there was a leading comment that was flush left before any
/// other content was written.
/// This is used when writing child blocks to make the parent chunk have the
/// right flush left value when a comment appears immediately inside the
/// block.
bool _firstFlushLeft = false;
/// Whether there is pending whitespace that depends on the number of
/// newlines in the source.
/// This is used to avoid calculating the newlines between tokens unless
/// actually needed since doing so is slow when done between every single
/// token pair.
bool get needsToPreserveNewlines =>
_pendingWhitespace == Whitespace.oneOrTwoNewlines ||
_pendingWhitespace == Whitespace.splitOrTwoNewlines ||
_pendingWhitespace == Whitespace.splitOrNewline;
/// The number of characters of code that can fit in a single line.
int get pageWidth => _formatter.pageWidth;
/// The current innermost rule.
Rule get rule => _rules.last;
ChunkBuilder(this._formatter, this._source)
: _parent = null,
_chunks = [] {
ChunkBuilder._(this._parent, this._formatter, this._source, this._chunks) {
/// Writes [string], the text for a single token, to the output.
/// By default, this also implicitly adds one level of nesting if we aren't
/// currently nested at all. We do this here so that if a comment appears
/// after any token within a statement or top-level form and that comment
/// leads to splitting, we correctly nest. Even pathological cases like:
/// import // comment
/// "this_gets_nested.dart";
/// If we didn't do this here, we'd have to call [nestExpression] after the
/// first token of practically every grammar production.
void write(String string) {
/// Writes a [WhitespaceChunk] of [type].
void writeWhitespace(Whitespace type) {
_pendingWhitespace = type;
/// Write a split owned by the current innermost rule.
/// If [flushLeft] is `true`, then forces the next line to start at column
/// one regardless of any indentation or nesting.
/// If [isDouble] is passed, forces the split to either be a single or double
/// newline. Otherwise, leaves it indeterminate.
/// If [nest] is `false`, ignores any current expression nesting. Otherwise,
/// uses the current nesting level. If unsplit, it expands to a space if
/// [space] is `true`.
Chunk split({bool flushLeft, bool isDouble, bool nest, bool space}) =>
flushLeft: flushLeft, isDouble: isDouble, nest: nest, space: space);
/// Outputs the series of [comments] and associated whitespace that appear
/// before [token] (which is not written by this).
/// The list contains each comment as it appeared in the source between the
/// last token written and the next one that's about to be written.
/// [linesBeforeToken] is the number of lines between the last comment (or
/// previous token if there are no comments) and the next token.
void writeComments(
List<SourceComment> comments, int linesBeforeToken, String token) {
// Edge case: if we require a blank line, but there exists one between
// some of the comments, or after the last one, then we don't need to
// enforce one before the first comment. Example:
// library foo;
// // comment
// class Bar {}
// Normally, a blank line is required after `library`, but since there is
// one after the comment, we don't need one before it. This is mainly so
// that commented out directives stick with their preceding group.
if (_pendingWhitespace == Whitespace.twoNewlines &&
comments.first.linesBefore < 2) {
if (linesBeforeToken > 1) {
_pendingWhitespace = Whitespace.newline;
} else {
for (var i = 1; i < comments.length; i++) {
if (comments[i].linesBefore > 1) {
_pendingWhitespace = Whitespace.newline;
// Edge case: if the comments are completely inline (i.e. just a series of
// block comments with no newlines before, after, or between them), then
// they will eat any pending newlines. Make sure that doesn't happen by
// putting the pending whitespace before the first comment and moving them
// to their own line. Turns this:
// library foo; /* a */ /* b */ import 'a.dart';
// into:
// library foo;
// /* a */ /* b */
// import 'a.dart';
if (linesBeforeToken == 0 &&
comments.every((comment) => comment.isInline)) {
if (_pendingWhitespace.minimumLines > 0) {
comments.first.linesBefore = _pendingWhitespace.minimumLines;
linesBeforeToken = 1;
// Write each comment and the whitespace between them.
for (var i = 0; i < comments.length; i++) {
var comment = comments[i];
// Don't emit a space because we'll handle it below. If we emit it here,
// we may get a trailing space if the comment needs a line before it.
if (_pendingWhitespace == {
_pendingWhitespace = Whitespace.none;
if (comment.linesBefore == 0) {
// If we're sitting on a split, move the comment before it to adhere it
// to the preceding text.
if (_shouldMoveCommentBeforeSplit(comment.text)) {
// The comment follows other text, so we need to decide if it gets a
// space before it or not.
if (_needsSpaceBeforeComment(comment)) _writeText(" ");
} else {
// The comment starts a line, so make sure it stays on its own line.
flushLeft: comment.flushLeft,
isDouble: comment.linesBefore > 1,
nest: true);
if (comment.selectionStart != null) {
startSelectionFromEnd(comment.text.length - comment.selectionStart);
if (comment.selectionEnd != null) {
endSelectionFromEnd(comment.text.length - comment.selectionEnd);
// Make sure there is at least one newline after a line comment and allow
// one or two after a block comment that has nothing after it.
var linesAfter;
if (i < comments.length - 1) {
linesAfter = comments[i + 1].linesBefore;
} else {
linesAfter = linesBeforeToken;
// Always force a newline after multi-line block comments. Prevents
// mistakes like:
// /**
// * Some doc comment.
// */ someFunction() { ... }
if (linesAfter == 0 && comments.last.text.contains("\n")) {
linesAfter = 1;
if (linesAfter > 0) _writeHardSplit(isDouble: linesAfter > 1, nest: true);
// If the comment has text following it (aside from a grouping character),
// it needs a trailing space.
if (_needsSpaceAfterLastComment(comments, token)) {
_pendingWhitespace =;
/// If the current pending whitespace allows some source discretion, pins
/// that down given that the source contains [numLines] newlines at that
/// point.
void preserveNewlines(int numLines) {
// If we didn't know how many newlines the user authored between the last
// token and this one, now we do.
switch (_pendingWhitespace) {
case Whitespace.splitOrNewline:
if (numLines > 0) {
_pendingWhitespace = Whitespace.nestedNewline;
} else {
_pendingWhitespace = Whitespace.none;
split(space: true);
case Whitespace.splitOrTwoNewlines:
if (numLines > 1) {
_pendingWhitespace = Whitespace.twoNewlines;
} else {
_pendingWhitespace = Whitespace.none;
split(space: true);
case Whitespace.oneOrTwoNewlines:
if (numLines > 1) {
_pendingWhitespace = Whitespace.twoNewlines;
} else {
_pendingWhitespace = Whitespace.newline;
/// Creates a new indentation level [spaces] deeper than the current one.
/// If omitted, [spaces] defaults to [Indent.block].
void indent([int spaces]) {
/// Discards the most recent indentation level.
void unindent() {
/// Starts a new span with [cost].
/// Each call to this needs a later matching call to [endSpan].
void startSpan([int cost = Cost.normal]) {
_openSpans.add(new OpenSpan(_currentChunkIndex, cost));
/// Ends the innermost span.
void endSpan() {
var openSpan = _openSpans.removeLast();
// A span that just covers a single chunk can't be split anyway.
var end = _currentChunkIndex;
if (openSpan.start == end) return;
// Add the span to every chunk that can split it.
var span = new Span(openSpan.cost);
for (var i = openSpan.start; i < end; i++) {
var chunk = _chunks[i];
if (!chunk.rule.isHardened) chunk.spans.add(span);
/// Starts a new [Rule].
/// If omitted, defaults to a new [Rule].
void startRule([Rule rule]) {
if (rule == null) rule = new Rule();
// If there are any pending lazy rules, start them now so that the proper
// stack ordering of rules is maintained.
void _activateRule(Rule rule) {
// See if any of the rules that contain this one care if it splits.
_rules.forEach((outer) {
if (!outer.splitsOnInnerRules) return;
/// Starts a new [Rule] that comes into play *after* the next whitespace
/// (including comments) is written.
/// This is used for operators who want to start a rule before the first
/// operand but not get forced to split if a comment appears before the
/// entire expression.
/// If [rule] is omitted, defaults to a new [Rule].
void startLazyRule([Rule rule]) {
if (rule == null) rule = new Rule();
/// Ends the innermost rule.
void endRule() {
if (_lazyRules.isNotEmpty) {
} else {
/// Pre-emptively forces all of the current rules to become hard splits.
/// This is called by [SourceVisitor] when it can determine that a rule will
/// will always be split. Turning it (and the surrounding rules) into hard
/// splits lets the writer break the output into smaller pieces for the line
/// splitter, which helps performance and avoids failing on very large input.
/// In particular, it's easy for the visitor to know that collections with a
/// large number of items must split. Doing that early avoids crashing the
/// splitter when it tries to recurse on huge collection literals.
void forceRules() => _handleHardSplit();
/// Begins a new expression nesting level [indent] spaces deeper than the
/// current one if it splits.
/// If [indent] is omitted, defaults to [Indent.expression]. If [now] is
/// `true`, commits the nesting change immediately instead of waiting until
/// after the next chunk of text is written.
void nestExpression({int indent, bool now}) {
if (now == null) now = false;
if (now) _nesting.commitNesting();
/// Discards the most recent level of expression nesting.
/// Expressions that are more nested will get increased indentation when split
/// if the previous line has a lower level of nesting.
/// If [now] is `false`, does not commit the nesting change until after the
/// next chunk of text is written.
void unnest({bool now}) {
if (now == null) now = true;
if (now) _nesting.commitNesting();
/// Marks the selection starting point as occurring [fromEnd] characters to
/// the left of the end of what's currently been written.
/// It counts backwards from the end because this is called *after* the chunk
/// of text containing the selection has been output.
void startSelectionFromEnd(int fromEnd) {
/// Marks the selection ending point as occurring [fromEnd] characters to the
/// left of the end of what's currently been written.
/// It counts backwards from the end because this is called *after* the chunk
/// of text containing the selection has been output.
void endSelectionFromEnd(int fromEnd) {
/// Captures the current nesting level as marking where subsequent block
/// arguments should start.
void startBlockArgumentNesting() {
/// Releases the last nesting level captured by [startBlockArgumentNesting].
void endBlockArgumentNesting() {
/// Starts a new block as a child of the current chunk.
/// Nested blocks are handled using their own independent [LineWriter].
ChunkBuilder startBlock(Chunk argumentChunk) {
var chunk = _chunks.last;
var builder =
new ChunkBuilder._(this, _formatter, _source, chunk.block.chunks);
// A block always starts off indented one level.
return builder;
/// Ends this [ChunkBuilder], which must have been created by [startBlock()].
/// Forces the chunk that owns the block to split if it can tell that the
/// block contents will always split. It does that by looking for hard splits
/// in the block. If [ignoredSplit] is given, that rule will be ignored
/// when determining if a block contains a hard split. If [forceSplit] is
/// `true`, the block is considered to always split.
/// Returns the previous writer for the surrounding block.
ChunkBuilder endBlock(Rule ignoredSplit, {bool forceSplit}) {
// If we don't already know if the block is going to split, see if it
// contains any hard splits or is longer than a page.
if (!forceSplit) {
var length = 0;
for (var chunk in _chunks) {
length += chunk.length + chunk.unsplitBlockLength;
if (length > _formatter.pageWidth) {
forceSplit = true;
if (chunk.rule != null &&
chunk.rule.isHardened &&
chunk.rule != ignoredSplit) {
forceSplit = true;
firstFlushLeft: _firstFlushLeft, forceSplit: forceSplit);
return _parent;
/// Finishes off the last chunk in a child block of this parent.
void _endChildBlock({bool firstFlushLeft, bool forceSplit}) {
// If there is a hard newline within the block, force the surrounding rule
// for it so that we apply that constraint.
if (forceSplit) forceRules();
// Write the split for the block contents themselves.
var chunk = _chunks.last;
chunk.applySplit(rule, _nesting.indentation, _blockArgumentNesting.last,
flushLeft: firstFlushLeft);
if (chunk.rule.isHardened) _handleHardSplit();
/// Finishes writing and returns a [SourceCode] containing the final output
/// and updated selection, if any.
SourceCode end() {
if (debug.traceChunkBuilder) {
debug.dumpChunks(0, _chunks);
var writer = new LineWriter(_formatter, _chunks);
var result = writer.writeLines(_formatter.indent,
isCompilationUnit: _source.isCompilationUnit);
var selectionStart;
var selectionLength;
if (_source.selectionStart != null) {
selectionStart = result.selectionStart;
var selectionEnd = result.selectionEnd;
// If we haven't hit the beginning and/or end of the selection yet, they
// must be at the very end of the code.
if (selectionStart == null) selectionStart = writer.length;
if (selectionEnd == null) selectionEnd = writer.length;
selectionLength = selectionEnd - selectionStart;
return new SourceCode(result.text,
uri: _source.uri,
isCompilationUnit: _source.isCompilationUnit,
selectionStart: selectionStart,
selectionLength: selectionLength);
/// Writes the current pending [Whitespace] to the output, if any.
/// This should only be called after source lines have been preserved to turn
/// any ambiguous whitespace into a concrete choice.
void _emitPendingWhitespace() {
// Output any pending whitespace first now that we know it won't be
// trailing.
switch (_pendingWhitespace) {
_writeText(" ");
case Whitespace.newline:
case Whitespace.nestedNewline:
_writeHardSplit(nest: true);
case Whitespace.newlineFlushLeft:
_writeHardSplit(flushLeft: true, nest: true);
case Whitespace.twoNewlines:
_writeHardSplit(isDouble: true);
case Whitespace.splitOrNewline:
case Whitespace.splitOrTwoNewlines:
case Whitespace.oneOrTwoNewlines:
// We should have pinned these down before getting here.
_pendingWhitespace = Whitespace.none;
/// Returns `true` if the last chunk is a split that should be moved after the
/// comment that is about to be written.
bool _shouldMoveCommentBeforeSplit(String comment) {
// Not if there is nothing before it.
if (_chunks.isEmpty) return false;
// Multi-line comments are always pushed to the next line.
if (comment.contains("\n")) return false;
var text = _chunks.last.text;
// A block comment following a comma probably refers to the following item.
if (text.endsWith(",") && comment.startsWith("/*")) return false;
// If the text before the split is an open grouping character, it looks
// better to keep it with the elements than with the bracket itself.
return !text.endsWith("(") && !text.endsWith("[") && !text.endsWith("{");
/// Returns `true` if [comment] appears to be a magic generic method comment.
/// Those get spaced a little differently to look more like real syntax:
/// int f/*<S, T>*/(int x) => 3;
bool _isGenericMethodComment(SourceComment comment) {
return comment.text.startsWith("/*<") || comment.text.startsWith("/*=");
/// Returns `true` if a space should be output between the end of the current
/// output and the subsequent comment which is about to be written.
/// This is only called if the comment is trailing text in the unformatted
/// source. In most cases, a space will be output to separate the comment
/// from what precedes it. This returns false if:
/// * This comment does begin the line in the output even if it didn't in
/// the source.
/// * The comment is a block comment immediately following a grouping
/// character (`(`, `[`, or `{`). This is to allow `foo(/* comment */)`,
/// et. al.
bool _needsSpaceBeforeComment(SourceComment comment) {
// Not at the start of the file.
if (_chunks.isEmpty) return false;
// Not at the start of a line.
if (!_chunks.last.canAddText) return false;
var text = _chunks.last.text;
if (text.endsWith("\n")) return false;
// Always put a space before line comments.
if (comment.isLineComment) return true;
// Magic generic method comments like "Foo/*<T>*/" don't get spaces.
if (_isGenericMethodComment(comment) &&
_trailingIdentifierChar.hasMatch(text)) {
return false;
// Block comments do not get a space if following a grouping character.
return !text.endsWith("(") && !text.endsWith("[") && !text.endsWith("{");
/// Returns `true` if a space should be output after the last comment which
/// was just written and the token that will be written.
bool _needsSpaceAfterLastComment(List<SourceComment> comments, String token) {
// Not if there are no comments.
if (comments.isEmpty) return false;
// Not at the beginning of a line.
if (!_chunks.last.canAddText) return false;
// Magic generic method comments like "Foo/*<T>*/" don't get spaces.
if (_isGenericMethodComment(comments.last) && token == "(") {
return false;
// Otherwise, it gets a space if the following token is not a delimiter or
// the empty string, for EOF.
return token != ")" &&
token != "]" &&
token != "}" &&
token != "," &&
token != ";" &&
token != "";
/// Appends a hard split with the current indentation and nesting (the latter
/// only if [nest] is `true`).
/// If [double] is `true` or `false`, forces a single or double line to be
/// output. Otherwise, it is left indeterminate.
/// If [flushLeft] is `true`, then the split will always cause the next line
/// to be at column zero. Otherwise, it uses the normal indentation and
/// nesting behavior.
void _writeHardSplit({bool isDouble, bool flushLeft, bool nest: false}) {
// A hard split overrides any other whitespace.
_pendingWhitespace = null;
_writeSplit(new Rule.hard(),
flushLeft: flushLeft, isDouble: isDouble, nest: nest);
/// Ends the current chunk (if any) with the given split information.
/// Returns the chunk.
Chunk _writeSplit(Rule rule,
{bool flushLeft, bool isDouble, bool nest, bool space}) {
if (nest == null) nest = true;
if (_chunks.isEmpty) {
if (flushLeft != null) _firstFlushLeft = flushLeft;
return null;
_chunks.last.applySplit(rule, _nesting.indentation,
nest ? _nesting.nesting : new NestingLevel(),
flushLeft: flushLeft, isDouble: isDouble, space: space);
if (_chunks.last.rule.isHardened) _handleHardSplit();
return _chunks.last;
/// Writes [text] to either the current chunk or a new one if the current
/// chunk is complete.
void _writeText(String text) {
if (_chunks.isNotEmpty && _chunks.last.canAddText) {
} else {
_chunks.add(new Chunk(text));
/// Returns true if we can divide the chunks at [index] and line split the
/// ones before and after that separately.
bool _canDivideAt(int i) {
// Don't divide after the last chunk.
if (i == _chunks.length - 1) return false;
var chunk = _chunks[i];
if (!chunk.rule.isHardened) return false;
if (chunk.nesting.isNested) return false;
if (chunk.isBlock) return false;
return true;
/// Pre-processes the chunks after they are done being written by the visitor
/// but before they are run through the line splitter.
/// Marks ranges of chunks that can be line split independently to keep the
/// batches we send to [LineSplitter] small.
void _divideChunks() {
// Harden all of the rules that we know get forced by containing hard
// splits, along with all of the other rules they constrain.
// Now that we know where all of the divided chunk sections are, mark the
// chunks.
for (var i = 0; i < _chunks.length; i++) {
/// Hardens the active rules when a hard split occurs within them.
void _handleHardSplit() {
if (_rules.isEmpty) return;
// If the current rule doesn't care, it will "eat" the hard split and no
// others will care either.
if (!_rules.last.splitsOnInnerRules) return;
// Start with the innermost rule. This will traverse the other rules it
// constrains.
/// Replaces all of the previously hardened rules with hard splits, along
/// with every rule that those constrain to also split.
/// This should only be called after all chunks have been written.
void _hardenRules() {
if (_hardSplitRules.isEmpty) return;
walkConstraints(rule) {
// Follow this rule's constraints, recursively.
for (var other in rule.constrainedRules) {
if (other == rule) continue;
if (!other.isHardened &&
rule.constrain(rule.fullySplitValue, other) ==
other.fullySplitValue) {
for (var rule in _hardSplitRules) {
// Discard spans in hardened chunks since we know for certain they will
// split anyway.
for (var chunk in _chunks) {
if (chunk.rule != null && chunk.rule.isHardened) {