lib/Format/ContinuationIndenter.h

//===--- ContinuationIndenter.h - Format C++ code ---------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief This file implements an indenter that manages the indentation of
/// continuations.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_FORMAT_CONTINUATION_INDENTER_H
#define LLVM_CLANG_FORMAT_CONTINUATION_INDENTER_H

#include "Encoding.h"
#include "clang/Format/Format.h"

namespace clang {
class SourceManager;

namespace format {

class AnnotatedLine;
struct FormatToken;
struct LineState;
struct ParenState;
class WhitespaceManager;

class ContinuationIndenter {
public:
  /// \brief Constructs a \c ContinuationIndenter to format \p Line starting in
  /// column \p FirstIndent.
  ContinuationIndenter(const FormatStyle &Style, SourceManager &SourceMgr,
                       const AnnotatedLine &Line, unsigned FirstIndent,
                       WhitespaceManager &Whitespaces,
                       encoding::Encoding Encoding,
                       bool BinPackInconclusiveFunctions);

  /// \brief Get the initial state, i.e. the state after placing the line's
  /// first token.
  LineState getInitialState();

  // FIXME: canBreak and mustBreak aren't strictly indentation-related. Find a
  // better home.
  /// \brief Returns \c true, if a line break after \p State is allowed.
  bool canBreak(const LineState &State);

  /// \brief Returns \c true, if a line break after \p State is mandatory.
  bool mustBreak(const LineState &State);

  /// \brief Appends the next token to \p State and updates information
  /// necessary for indentation.
  ///
  /// Puts the token on the current line if \p Newline is \c false and adds a
  /// line break and necessary indentation otherwise.
  ///
  /// If \p DryRun is \c false, also creates and stores the required
  /// \c Replacement.
  unsigned addTokenToState(LineState &State, bool Newline, bool DryRun);

  /// \brief Get the column limit for this line. This is the style's column
  /// limit, potentially reduced for preprocessor definitions.
  unsigned getColumnLimit() const;

private:
  /// \brief Mark the next token as consumed in \p State and modify its stacks
  /// accordingly.
  unsigned moveStateToNextToken(LineState &State, bool DryRun, bool Newline);

  /// \brief If the current token sticks out over the end of the line, break
  /// it if possible.
  ///
  /// \returns An extra penalty if a token was broken, otherwise 0.
  ///
  /// The returned penalty will cover the cost of the additional line breaks and
  /// column limit violation in all lines except for the last one. The penalty
  /// for the column limit violation in the last line (and in single line
  /// tokens) is handled in \c addNextStateToQueue.
  unsigned breakProtrudingToken(const FormatToken &Current, LineState &State,
                                bool DryRun);

  FormatStyle Style;
  SourceManager &SourceMgr;
  const AnnotatedLine &Line;
  const unsigned FirstIndent;
  WhitespaceManager &Whitespaces;
  encoding::Encoding Encoding;
  bool BinPackInconclusiveFunctions;
};

struct ParenState {
  ParenState(unsigned Indent, unsigned LastSpace, bool AvoidBinPacking,
             bool NoLineBreak)
      : Indent(Indent), LastSpace(LastSpace), FirstLessLess(0),
        BreakBeforeClosingBrace(false), QuestionColumn(0),
        AvoidBinPacking(AvoidBinPacking), BreakBeforeParameter(false),
        NoLineBreak(NoLineBreak), ColonPos(0), StartOfFunctionCall(0),
        StartOfArraySubscripts(0), NestedNameSpecifierContinuation(0),
        CallContinuation(0), VariablePos(0), ContainsLineBreak(false) {}

  /// \brief The position to which a specific parenthesis level needs to be
  /// indented.
  unsigned Indent;

  /// \brief The position of the last space on each level.
  ///
  /// Used e.g. to break like:
  /// functionCall(Parameter, otherCall(
  ///                             OtherParameter));
  unsigned LastSpace;

  /// \brief The position the first "<<" operator encountered on each level.
  ///
  /// Used to align "<<" operators. 0 if no such operator has been encountered
  /// on a level.
  unsigned FirstLessLess;

  /// \brief Whether a newline needs to be inserted before the block's closing
  /// brace.
  ///
  /// We only want to insert a newline before the closing brace if there also
  /// was a newline after the beginning left brace.
  bool BreakBeforeClosingBrace;

  /// \brief The column of a \c ? in a conditional expression;
  unsigned QuestionColumn;

  /// \brief Avoid bin packing, i.e. multiple parameters/elements on multiple
  /// lines, in this context.
  bool AvoidBinPacking;

  /// \brief Break after the next comma (or all the commas in this context if
  /// \c AvoidBinPacking is \c true).
  bool BreakBeforeParameter;

  /// \brief Line breaking in this context would break a formatting rule.
  bool NoLineBreak;

  /// \brief The position of the colon in an ObjC method declaration/call.
  unsigned ColonPos;

  /// \brief The start of the most recent function in a builder-type call.
  unsigned StartOfFunctionCall;

  /// \brief Contains the start of array subscript expressions, so that they
  /// can be aligned.
  unsigned StartOfArraySubscripts;

  /// \brief If a nested name specifier was broken over multiple lines, this
  /// contains the start column of the second line. Otherwise 0.
  unsigned NestedNameSpecifierContinuation;

  /// \brief If a call expression was broken over multiple lines, this
  /// contains the start column of the second line. Otherwise 0.
  unsigned CallContinuation;

  /// \brief The column of the first variable name in a variable declaration.
  ///
  /// Used to align further variables if necessary.
  unsigned VariablePos;

  /// \brief \c true if this \c ParenState already contains a line-break.
  ///
  /// The first line break in a certain \c ParenState causes extra penalty so
  /// that clang-format prefers similar breaks, i.e. breaks in the same
  /// parenthesis.
  bool ContainsLineBreak;

  bool operator<(const ParenState &Other) const {
    if (Indent != Other.Indent)
      return Indent < Other.Indent;
    if (LastSpace != Other.LastSpace)
      return LastSpace < Other.LastSpace;
    if (FirstLessLess != Other.FirstLessLess)
      return FirstLessLess < Other.FirstLessLess;
    if (BreakBeforeClosingBrace != Other.BreakBeforeClosingBrace)
      return BreakBeforeClosingBrace;
    if (QuestionColumn != Other.QuestionColumn)
      return QuestionColumn < Other.QuestionColumn;
    if (AvoidBinPacking != Other.AvoidBinPacking)
      return AvoidBinPacking;
    if (BreakBeforeParameter != Other.BreakBeforeParameter)
      return BreakBeforeParameter;
    if (NoLineBreak != Other.NoLineBreak)
      return NoLineBreak;
    if (ColonPos != Other.ColonPos)
      return ColonPos < Other.ColonPos;
    if (StartOfFunctionCall != Other.StartOfFunctionCall)
      return StartOfFunctionCall < Other.StartOfFunctionCall;
    if (StartOfArraySubscripts != Other.StartOfArraySubscripts)
      return StartOfArraySubscripts < Other.StartOfArraySubscripts;
    if (CallContinuation != Other.CallContinuation)
      return CallContinuation < Other.CallContinuation;
    if (VariablePos != Other.VariablePos)
      return VariablePos < Other.VariablePos;
    if (ContainsLineBreak != Other.ContainsLineBreak)
      return ContainsLineBreak < Other.ContainsLineBreak;
    return false;
  }
};

/// \brief The current state when indenting a unwrapped line.
///
/// As the indenting tries different combinations this is copied by value.
struct LineState {
  /// \brief The number of used columns in the current line.
  unsigned Column;

  /// \brief The token that needs to be next formatted.
  const FormatToken *NextToken;

  /// \brief \c true if this line contains a continued for-loop section.
  bool LineContainsContinuedForLoopSection;

  /// \brief The level of nesting inside (), [], <> and {}.
  unsigned ParenLevel;

  /// \brief The \c ParenLevel at the start of this line.
  unsigned StartOfLineLevel;

  /// \brief The lowest \c ParenLevel on the current line.
  unsigned LowestLevelOnLine;

  /// \brief The start column of the string literal, if we're in a string
  /// literal sequence, 0 otherwise.
  unsigned StartOfStringLiteral;

  /// \brief A stack keeping track of properties applying to parenthesis
  /// levels.
  std::vector<ParenState> Stack;

  /// \brief Ignore the stack of \c ParenStates for state comparison.
  ///
  /// In long and deeply nested unwrapped lines, the current algorithm can
  /// be insufficient for finding the best formatting with a reasonable amount
  /// of time and memory. Setting this flag will effectively lead to the
  /// algorithm not analyzing some combinations. However, these combinations
  /// rarely contain the optimal solution: In short, accepting a higher
  /// penalty early would need to lead to different values in the \c
  /// ParenState stack (in an otherwise identical state) and these different
  /// values would need to lead to a significant amount of avoided penalty
  /// later.
  ///
  /// FIXME: Come up with a better algorithm instead.
  bool IgnoreStackForComparison;

  /// \brief Comparison operator to be able to used \c LineState in \c map.
  bool operator<(const LineState &Other) const {
    if (NextToken != Other.NextToken)
      return NextToken < Other.NextToken;
    if (Column != Other.Column)
      return Column < Other.Column;
    if (LineContainsContinuedForLoopSection !=
        Other.LineContainsContinuedForLoopSection)
      return LineContainsContinuedForLoopSection;
    if (ParenLevel != Other.ParenLevel)
      return ParenLevel < Other.ParenLevel;
    if (StartOfLineLevel != Other.StartOfLineLevel)
      return StartOfLineLevel < Other.StartOfLineLevel;
    if (LowestLevelOnLine != Other.LowestLevelOnLine)
      return LowestLevelOnLine < Other.LowestLevelOnLine;
    if (StartOfStringLiteral != Other.StartOfStringLiteral)
      return StartOfStringLiteral < Other.StartOfStringLiteral;
    if (IgnoreStackForComparison || Other.IgnoreStackForComparison)
      return false;
    return Stack < Other.Stack;
  }
};

} // end namespace format
} // end namespace clang

#endif // LLVM_CLANG_FORMAT_CONTINUATION_INDENTER_H