[cfe-dev] Advanced Rewriting

Rafael·Stahl via cfe-dev cfe-dev at lists.llvm.org
Mon Jul 16 08:08:11 PDT 2018


Hey everyone

The rewriting API of Clang operates on the source code in textual form. 
The user can use AST nodes to figure out what to replace, but in the end 
he has to remove and insert snippets in a linear piece of text.

This is very inconvenient when it is required to restructure and nest 
replacements. The involvement of macros makes a manual process even more 
difficult. See some recent threads expressing difficulty with the API 
[1][2].

What do I mean by "nested replacements"? For example in the following:

     int i = x + s->a;

I would want to replace the BinaryOperator with a function call and the 
MemberExpr with some constant:

     int i = Addition(x, 7);

When keeping the two replacement rules independent of each other, 
achieving this with the current API is extremely difficult. More so when 
macros are involved.

I am proposing some kind of helper that aims to solve these issues by 
providing an interface that offers to directly replace AST nodes and a 
mechanism to nest AST node replacements - without having to worry about 
macros.

Potential usage:

- Develop a class that derives from StmtToRewrite to define how 
replacements should happen:

     class RewriteAdds : public cu::StmtToRewrite
     {
     public:
         std::string makeReplaceStr() const override
         {
             auto binOp = dyn_cast<BinaryOperator>(replaceS);
             return "Addition(" + 
getMgr()->getReplaced(binOp->getLHS()).strToInsert + ", " +
getMgr()->getReplaced(binOp->getRHS()).strToInsert + ")";
         }
     };

     class RewriteMembs : public cu::StmtToRewrite
     {
     public:
         std::string makeReplaceStr() const override
         {
             return "7";
         }
     };

- Construct a RewriteManager:

     cu::RewriteManager mgr(ACtx, PP);

- Add rewriting operations to the manager:

     // std::vector<const Stmt *> AddStmts = /* matched from 
binaryOperator() with plus */
     // std::vector<const Stmt *> MembStmts = /* matched from 
memberExpr() */
     for (const auto &S : AddStmts) mgr.registerStmt<RewriteAdds>(S);
     for (const auto &S : MembStmts) mgr.registerStmt<RewriteMembs>(S);

- Retrieve and apply the results:

     clang::Rewriter rewriter(SM, LangOpts);
     for (const auto &r : mgr.getReplacements()) {
         rewriter.RemoveText(r.rangeToRemove);
         rewriter.InsertText(r.rangeToRemove.getBegin(), r.strToInsert);
     }


At the end of this mail is my low quality code that kind-of implements 
this. TLDR:

- Build a hierarchy of stmts to replace and keep track of which 
replacements must be combined
- Move further up in the AST if these replacements are inside a macro
- Recursively lex the file and look for replacements outside-in by 
spelling locations. Expand any macros that are encountered during this. 
The re-lexing idea is based on the hint in [3].

The code has the following shortcomings:

- I do not know how to distinguish macro argument expansions within 
macros. For example in "#define FOO(a) a + a" the two "a"s expand to 
different AST nodes that could be replaced with different rules. This is 
an important issue, because it can lead to completely broken code with 
nesting.
- Limited to Stmts, when Decls should be supported too.
- Very un-optimized with lexing the entire source file many times. Easy 
to solve, but didn't want to raise the complexity further for now.
- Could keep written code more clean by only expanding macros if 
required. For example not required if just a macro arg is replaced and 
all expansions would be the same.


I am very interested in your general thoughts. I'm not very experienced 
with clang, but this was my vision how I would want to do replacements. 
Are you interested in getting this into clang? I would need help with 
ironing out the remaining issues.

-Rafael


[1] http://lists.llvm.org/pipermail/cfe-dev/2018-July/058430.html
[2] http://lists.llvm.org/pipermail/cfe-dev/2018-June/058213.html
[3] http://lists.llvm.org/pipermail/cfe-dev/2017-August/055079.html



----------------------------------------

RewriteManager.h

----------------------------------------

#ifndef CLANGUTIL_REWRITEMANAGER_H
#define CLANGUTIL_REWRITEMANAGER_H

#include "ClangUtil/SourceRangeLess.h"
#include "make_unique.h"
#include "clang/AST/AST.h"
#include <vector>
#include <map>


// TODO extend to decls


namespace cu
{
// Represents a statement in the original AST that should be rewritten. 
To implement recursive replacements, call
// getMgr()->getReplaced() on any AST node within the makeReplaceStr 
callback.
class StmtToRewrite
{
     friend class RewriteManager;

public:
     // Returns the enclosing RewriteManager.
     class RewriteManager *getMgr() const;
     // Override this to build a replacement string. Implement recursive 
replacements with RewriteManager::getReplaced.
     virtual std::string makeReplaceStr() const = 0;

     // The statement to replace.
     const clang::Stmt *replaceS = nullptr;

private:
     RewriteManager *m_mgr;
};

struct RewriteOperation
{
     clang::SourceRange rangeToRemove;
     std::string strToInsert;
};

// A class for managing replacements of AST nodes. It allows to 
specifically target AST nodes instead of raw source
// locations to enable easy replacements involving macros and nested 
replacements.
// For extended documentation see: doc/rewriting.md
class RewriteManager
{
public:
     RewriteManager(clang::ASTContext &ACtx, clang::Preprocessor &PP);

     clang::ASTContext &getACtx() const { return ACtx; }

     // Registers a StmtToRewrite for use with getReplacements. Call 
this on all
     // statements that should be rewritten before calling any rewriting 
functions.
     void registerStmt(std::unique_ptr<StmtToRewrite> S);

     // Helper for constructing the custom type from a Stmt.
     template <typename T, typename... Args>
     void registerStmt(const clang::Stmt *S, Args... args)
     {
         auto p = std::make_unique<T>(std::forward<Args>(args)...);
         p->replaceS = S;
         registerStmt(std::move(p));
     }

     // Get the full replacement of an AST node. Note that this function 
removes any replaced statements from the work
     // list, so calling it twice will only replace the first time.
     RewriteOperation getReplaced(const clang::Stmt *S);
     // Get all replacements. These may be fewer than the requested ones 
because of nesting.
     std::vector<RewriteOperation> getReplacements();

private:
     std::string getExpandedCode(const clang::Stmt *toReplaceS);

private:
     clang::ASTContext &ACtx;
     const clang::LangOptions &LangOpts;
     clang::SourceManager &SM;
     clang::Preprocessor &PP;

     // Manages the pending replacements.
     class WorkList
     {
     public:
         typedef std::map<clang::SourceRange, std::vector<const 
StmtToRewrite *>> RangeToRepMap;

         WorkList(clang::ASTContext &ACtx, clang::SourceManager &SM);

         bool isStmtPending(const clang::Stmt *S) const;
         void addStmt(std::unique_ptr<StmtToRewrite> S);
         const RangeToRepMap &getRangeToReplacementsMap() const;
         std::vector<const StmtToRewrite *> getSortedReplacements() const;
         void markDone(const StmtToRewrite *S);
         void cleanup();

     private:
         clang::ASTContext &ACtx;
         clang::SourceManager &SM;
         std::vector<std::unique_ptr<StmtToRewrite>> m_pending;
         std::vector<std::unique_ptr<StmtToRewrite>> m_done;
         RangeToRepMap m_rangeToReplacements;
     };

     WorkList m_workList;
};

} // namespace cu

#endif



----------------------------------------

RewriteManager.cpp

----------------------------------------

#include "ClangUtil/RewriteManager.h"
#include "ClangUtil/ASTUtil.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "clang/Lex/TokenConcatenation.h"
#include "clang/Lex/MacroArgs.h"


using namespace cu;


// Returns a Stmt that is the first parent of startS whose expansion 
range is within the given range.
static const clang::Stmt *GetFullMacroStmt(clang::SourceRange range, 
const clang::Stmt *startS, clang::ASTContext &ACtx)
{
     auto &SM = ACtx.getSourceManager();

     // Walk the tree upwards until ST does no longer expand to within 
range.
     const clang::Stmt *ST = startS;
     while (true)
     {
         const auto &parents = ACtx.getParents(*ST);
         if (parents.empty())
         {
             break;
         }
         auto childS = ST;
         ST = parents[0].get<clang::Stmt>();
         if (!ST)
         {
             if (auto D = parents[0].get<clang::Decl>())
             {
                 const auto &parentsD = ACtx.getParents(*D);
                 if (parentsD.empty())
                 {
                     break;
                 }
                 ST = parentsD[0].get<clang::Stmt>();
                 if (!ST)
                 {
                     break;
                 }
             }
             else
             {
                 break;
             }
         }

         auto exLocS = SM.getExpansionLoc(ST->getLocStart());
         auto exLocE = SM.getExpansionLoc(ST->getLocEnd());
         if (SM.isBeforeInTranslationUnit(exLocS, range.getBegin()) ||
             SM.isBeforeInTranslationUnit(range.getEnd(), exLocE))
         {
             return childS;
         }
     }

     return nullptr;
}


RewriteManager *StmtToRewrite::getMgr() const
{
     return m_mgr;
}


RewriteManager::WorkList::WorkList(clang::ASTContext &ACtx, 
clang::SourceManager &SM) : ACtx(ACtx), SM(SM) {}
bool RewriteManager::WorkList::isStmtPending(const clang::Stmt *S) const
{
     for (const auto &r : m_pending)
     {
         if (r->replaceS == S)
         {
             return true;
         }
     }
     return false;
}
void RewriteManager::WorkList::addStmt(std::unique_ptr<StmtToRewrite> S)
{
     // Use the expansion range for maximal replacement flexibility in 
macros.
     auto replaceRange = 
SM.getExpansionRange(S->replaceS->getSourceRange());

     // TODO not quite correct.
     /*auto sortRanges = [&](std::vector<const StmtToRewrite *> &vec) {
         std::sort(vec.begin(), vec.end(), [&](const StmtToRewrite *lhs, 
const StmtToRewrite *rhs) {
             auto lhsRange = 
SM.getExpansionRange(lhs->replaceS->getSourceRange());
             auto rhsRange = 
SM.getExpansionRange(rhs->replaceS->getSourceRange());
             return IsContained(rhsRange, lhsRange, SM);
         });
     };*/

     // Establish hierarchical relation between all ranges.
     bool found = false;
     // First, check if this range is within one we already have.
     for (auto &r : m_rangeToReplacements)
     {
         if (IsContained(replaceRange, r.first, SM))
         {
             // Insert in a sorted order.
             for (auto it = r.second.begin(); it != r.second.end(); ++it)
             {
                 //auto testRange = 
SM.getExpansionRange((*it)->replaceS->getSourceRange());
                 // if (IsContained(testRange, replaceRange, SM))
                 if (IsParent(S->replaceS, (*it)->replaceS, ACtx))
                 {
                     r.second.insert(it, S.get());
                     found = true;
                     break;
                 }
             }
             if (!found)
             {
                 r.second.push_back(S.get());
                 found = true;
             }
             break;
         }
     }
     // Not within existing range, add as new top-level range.
     if (!found)
     {
         // Check if any existing ranges are contained within the new one.
         std::vector<const StmtToRewrite *> moveThese;
         auto it = m_rangeToReplacements.begin();
         while (it != m_rangeToReplacements.end())
         {
             if (IsContained(it->first, replaceRange, SM))
             {
                 moveThese.insert(moveThese.end(), it->second.begin(), 
it->second.end());
                 it = m_rangeToReplacements.erase(it);
             }
             else
             {
                 ++it;
             }
         }
         auto &accesses = m_rangeToReplacements[replaceRange];
         // The order is important here. We want the first element to be 
the one that spans the full range.
         accesses.push_back(S.get());
         // TODO sort "moveThese".
         accesses.insert(accesses.end(), moveThese.begin(), 
moveThese.end());
     }

     int count = 0;
     for (const auto &r : m_rangeToReplacements)
     {
         printf("range %i\n", count++);
         for (const auto &a : r.second)
         {
             printf("replacement:\n");
             a->replaceS->dump();
         }
     }

     m_pending.push_back(std::move(S));
}
const RewriteManager::WorkList::RangeToRepMap 
&RewriteManager::WorkList::getRangeToReplacementsMap() const
{
     return m_rangeToReplacements;
}
std::vector<const StmtToRewrite *> 
RewriteManager::WorkList::getSortedReplacements() const
{
     std::vector<const StmtToRewrite *> result;
     for (auto &r : m_rangeToReplacements)
     {
         result.insert(result.end(), r.second.begin(), r.second.end());
     }
     return result;
}
void RewriteManager::WorkList::markDone(const StmtToRewrite *S)
{
     // Remove from hierarchy.
     for (auto &r : m_rangeToReplacements)
     {
         r.second.erase(std::remove(r.second.begin(), r.second.end(), 
S), r.second.end());
     }

     // Move from pending to done list.
     auto it = std::find_if(m_pending.begin(), m_pending.end(),
                            [&](const std::unique_ptr<StmtToRewrite> 
&rep) { return rep.get() == S; });
     if (it == m_pending.end())
     {
         throw std::runtime_error("Did not find replacement to mark as 
done");
     }
     m_done.push_back(std::move(*it));
     m_pending.erase(it);
}
void RewriteManager::WorkList::cleanup()
{
     m_done.clear();
}


RewriteManager::RewriteManager(clang::ASTContext &ACtx, 
clang::Preprocessor &PP)
     : ACtx(ACtx), LangOpts(ACtx.getLangOpts()), 
SM(ACtx.getSourceManager()), PP(PP), m_workList(ACtx, SM)
{
}

void RewriteManager::registerStmt(std::unique_ptr<StmtToRewrite> S)
{
     if (!S->replaceS)
     {
         throw std::runtime_error("Must set replaceS");
     }

     if (m_workList.isStmtPending(S->replaceS))
     {
         throw std::runtime_error("This Stmt will already be replaced");
     }

     S->m_mgr = this;
     m_workList.addStmt(std::move(S));
}

RewriteOperation RewriteManager::getReplaced(const clang::Stmt *S)
{
     auto range = SM.getExpansionRange(S->getSourceRange());
     return { range, getExpandedCode(S) };
}

std::vector<RewriteOperation> RewriteManager::getReplacements()
{
     std::vector<RewriteOperation> results;

     for (auto &rangeAndAccesses : m_workList.getRangeToReplacementsMap())
     {
         auto &range = rangeAndAccesses.first;
         auto &accesses = rangeAndAccesses.second;

         // Cannot replace something inside a macro because it would 
replace all expansions instead of just the selected
         // AST node. So in a first step, get an enclosing statement 
that is no longer inside a macro.
         // TODO we could keep the original code more clean by not 
expanding macro args if the whole expansion does not
         // contain the macro arg more than once.
         auto macroS = GetFullMacroStmt(range, accesses[0]->replaceS, ACtx);

         results.push_back(getReplaced(macroS));

         // TODO we could run clang-format on the replacements. this 
would especially benefit long macro expansions.
     }

     m_workList.cleanup();

     return results;
}

std::string RewriteManager::getExpandedCode(const clang::Stmt *toReplaceS)
{
     // TODO performance optimization. this is parsing way more than 
required.

     using namespace clang;

     printf("getExpandedCode:\n");
     toReplaceS->dump();

     std::string out;

     auto toReplaceExpStart = SM.getExpansionLoc(toReplaceS->getLocStart());
     auto toReplaceExpEnd = SM.getExpansionLoc(toReplaceS->getLocEnd());
     auto toReplaceSpellStart = 
SM.getSpellingLoc(toReplaceS->getLocStart());
     auto toReplaceSpellEnd = SM.getSpellingLoc(toReplaceS->getLocEnd());

     auto FID = SM.getFileID(SM.getExpansionLoc(toReplaceS->getLocStart()));

     // The following is inspired by: 
clang/Rewrite/HTMLRewrite.cpp:HighlightMacros

     // Re-lex the raw token stream into a token buffer.
     std::vector<Token> TokenStream;

     const llvm::MemoryBuffer *FromFile = SM.getBuffer(FID);
     Lexer L(FID, FromFile, SM, PP.getLangOpts());

     // Lex all the tokens in raw mode, to avoid entering #includes or 
expanding
     // macros.
     while (1)
     {
         Token Tok;
         L.LexFromRawLexer(Tok);

         // If this is a # at the start of a line, discard it from the 
token stream.
         // We don't want the re-preprocess step to see #defines, 
#includes or other
         // preprocessor directives.
         if (Tok.is(tok::hash) && Tok.isAtStartOfLine())
             continue;

         // If this is a ## token, change its kind to unknown so that 
repreprocessing
         // it will not produce an error.
         if (Tok.is(tok::hashhash))
             Tok.setKind(tok::unknown);

         // If this raw token is an identifier, the raw lexer won't have 
looked up
         // the corresponding identifier info for it.  Do this now so 
that it will be
         // macro expanded when we re-preprocess it.
         if (Tok.is(tok::raw_identifier))
             PP.LookUpIdentifierInfo(Tok);

         TokenStream.push_back(Tok);

         for (auto &rep : m_workList.getSortedReplacements())
         {
             auto repS = rep->replaceS;
             auto spellLoc = SM.getSpellingLoc(repS->getLocStart());
             if (SM.getSpellingLoc(Tok.getLocation()) == spellLoc)
             {
                 //
             }
         }

         if (Tok.is(tok::eof))
             break;
     }

     // Temporarily change the diagnostics object so that we ignore any 
generated
     // diagnostics from this pass.
     DiagnosticsEngine TmpDiags(PP.getDiagnostics().getDiagnosticIDs(), 
&PP.getDiagnostics().getDiagnosticOptions(),
                                new IgnoringDiagConsumer);

     // Copy the preprocessor and all of its state.
     auto PPOpts = 
std::make_shared<PreprocessorOptions>(PP.getPreprocessorOpts());
     LangOptions LO = PP.getLangOpts();
     Preprocessor TmpPP(PPOpts, TmpDiags, LO, SM, PP.getPCMCache(), 
PP.getHeaderSearchInfo(), PP.getModuleLoader(),
PP.getIdentifierTable().getExternalIdentifierLookup());
     TmpPP.Initialize(PP.getTargetInfo(), PP.getAuxTargetInfo());
     TmpPP.setExternalSource(PP.getExternalSource());
     TmpPP.setPreprocessedOutput(true);

     std::map<const clang::IdentifierInfo *, bool> MacroPreviouslyEnabled;
     for (const auto &m : PP.macros())
     {
         // printf("PREDEF MACRO: %s\n", m.first->getName().str().c_str());
         TmpPP.getMacroDefinition(m.first);

         for (const auto &tmpm : TmpPP.macros())
         {
             if (tmpm.first == m.first)
             {
                 auto MD = m.second.getLatest();
                 auto MI = MD->getMacroInfo();
                 // If this is a recursive call we might be in a macro 
expansion and the macro might be disabled. We need
                 // to enable it for now so that all expansions work. 
Restore it later.
                 MacroPreviouslyEnabled[tmpm.first] = MI->isEnabled();
                 if (!MI->isEnabled())
                 {
                     MD->getMacroInfo()->EnableMacro();
                 }

                 // This should not change anything since we just copy 
data over.
                 auto &mutableState = 
const_cast<std::remove_const<decltype(tmpm.second)>::type &>(tmpm.second);
                 mutableState.setLatest(MD);
                 break;
             }
         }
     }

     class MacroArgCollector : public clang::PPCallbacks
     {
     public:
         MacroArgCollector(Preprocessor &TmpPP) : TmpPP(TmpPP) {}

         void MacroExpands(const Token &Tok, const MacroDefinition &MD, 
SourceRange Range, const MacroArgs *Args) override
         {
             if (!Args)
             {
                 return;
             }
             printf("GOT MACRO ARGS EXPANSION CALLBACK\n");
             for (int i = 0; i < (int)Args->getNumMacroArguments(); i++)
             {
                 auto TokUnex = Args->getUnexpArgument(i);
                 // Thats just non-const for a cache, so should be fine.
                 auto TokPreExp = const_cast<MacroArgs 
*>(Args)->getPreExpArgument(i, TmpPP);
                 printf("unexp: %s\n", TmpPP.getSpelling(*TokUnex).c_str());
                 for (const auto &T : TokPreExp)
                 {
                     printf("preexp: %s\n", TmpPP.getSpelling(T).c_str());
                 }
             }
         }

         Preprocessor &TmpPP;
     };
TmpPP.addPPCallbacks(std::make_unique<MacroArgCollector>(TmpPP));
     // Instead: collect the macro arg info in the law lexing step 
above. or do another pass that uses the PP but without expansions.

     /*printf("DUMP MACRO INFO\n");
     for (const auto &m : PP.macros())
         PP.dumpMacroInfo(m.first);
     printf("---\n");
     for (const auto &m : TmpPP.macros())
         TmpPP.dumpMacroInfo(m.first);
     printf("DUMP MACRO INFO END\n");*/

     DiagnosticsEngine *OldDiags = &TmpPP.getDiagnostics();

     // Inform the preprocessor that we don't want comments.
     TmpPP.SetCommentRetentionState(false, false);

     // We don't want pragmas either. Although we filtered out #pragma, 
removing
     // _Pragma and __pragma is much harder.
     bool PragmasPreviouslyEnabled = TmpPP.getPragmasEnabled();
     TmpPP.setPragmasEnabled(false);

     // Enter the tokens we just lexed.  This will cause them to be 
macro expanded
     // but won't enter sub-files (because we removed #'s).
     TmpPP.EnterTokenStream(TokenStream, false);

     TokenConcatenation ConcatInfo(TmpPP);

     // Lex all the tokens.
     Token Tok;
     TmpPP.Lex(Tok);

     std::map<SourceLocation, int> slocIdx;

     auto checkReplacement = [&]() {
         for (auto &rep : m_workList.getSortedReplacements())
         {
             // auto rep = r.second.get();
             auto repS = rep->replaceS;
             auto spellLoc = SM.getSpellingLoc(repS->getLocStart());
             // TODO we need to check here if the repS spans the full 
range (or largest?)
             if (SM.getSpellingLoc(Tok.getLocation()) == spellLoc)
             {
                 if (slocIdx[spellLoc] == 7)
                 {
                     // replace
                 }
                 slocIdx[spellLoc]++;

                 // Done replacing that one, but have to keep it alive 
until we're done with it.
                 m_workList.markDone(rep);

                 printf("[[[\n");
                 auto repStr = rep->makeReplaceStr();
                 printf("REPLACED: %s ]]]\n", repStr.c_str());
                 out += repStr;

                 // Skip ahead until after the whole replacement.
                 auto repEnd = SM.getSpellingLoc(repS->getLocEnd());
                 while (repEnd != SM.getSpellingLoc(Tok.getLocation()))
                 {
                     TmpPP.Lex(Tok);
                     assert(!Tok.is(tok::eof) && "End not found");
                 }

                 // Eat one more since we stopped at the end token and 
we want to continue after it.
                 TmpPP.Lex(Tok);

                 return true;
             }
         }
         return false;
     };

     while (Tok.isNot(tok::eof))
     {
         printf("TOKEN: %s\n", TmpPP.getSpelling(Tok).c_str());

         auto TokLoc = Tok.getLocation();
         auto TokExp = SM.getExpansionLoc(TokLoc);
         if (SM.isBeforeInTranslationUnit(toReplaceExpEnd, TokExp))
         {
             // Anything after the Stmt we want to replace is not 
interesting.
             break;
         }

         // Skip ahead until we are at the expansion start of the Stmt 
we want to replace.
         if (!SM.isBeforeInTranslationUnit(TokLoc, toReplaceExpStart))
         {
             if (TokLoc.isMacroID())
             {
                 // This is the first token of a macro expansion.
                 auto LLoc = SM.getExpansionRange(TokLoc);

                 // Ignore tokens whose instantiation location was not 
the main file.
                 if (SM.getFileID(LLoc.first) != FID)
                 {
                     TmpPP.Lex(Tok);
                     continue;
                 }

                 assert(SM.getFileID(LLoc.second) == FID &&
                        "Start and end of expansion must be in the same 
ultimate file!");

                 bool stopOutputOnNextToken = false;
                 bool toReplaceStartsInMacro = toReplaceExpStart == TokExp;
                 bool toReplaceEndsInMacro = toReplaceExpEnd == TokExp;
                 bool startedOutput = false;

                 Token PrevPrevTok;
                 Token PrevTok = Tok;

                 while (!Tok.is(tok::eof) && 
SM.getExpansionLoc(Tok.getLocation()) == LLoc.first)
                 {
                     printf("TOKEN (in macro): %s\n", 
TmpPP.getSpelling(Tok).c_str());

                     auto TokSpell = SM.getSpellingLoc(Tok.getLocation());
                     if (stopOutputOnNextToken)
                     {
                         break;
                     }
                     if (toReplaceEndsInMacro && TokSpell == 
toReplaceSpellEnd)
                     {
                         stopOutputOnNextToken = true;
                     }

                     if (toReplaceStartsInMacro && !startedOutput)
                     {
                         if (TokSpell == toReplaceSpellStart)
                         {
                             startedOutput = true;
                         }
                         else
                         {
                             TmpPP.Lex(Tok);
                             continue;
                         }
                     }

                     // If the tokens were already space separated, or 
if they must be to avoid
                     // them being implicitly pasted, add a space 
between them.
                     if (Tok.hasLeadingSpace() || 
ConcatInfo.AvoidConcat(PrevPrevTok, PrevTok, Tok))
                         out += ' ';

                     if (checkReplacement())
                     {
                         continue;
                     }

                     out += TmpPP.getSpelling(Tok);
                     TmpPP.Lex(Tok);
                 }
                 if (stopOutputOnNextToken)
                 {
                     break;
                 }
             }
             else
             {
                 if (checkReplacement())
                 {
                     continue;
                 }

                 // Output original code because we are outside of a 
replacement.
                 out += TmpPP.getSpelling(Tok);
                 TmpPP.Lex(Tok);
             }
         }
         else
         {
             TmpPP.Lex(Tok);
         }
     }

     // Restore the preprocessor's old state.
     TmpPP.setDiagnostics(*OldDiags);
     TmpPP.setPragmasEnabled(PragmasPreviouslyEnabled);

     for (const auto &tmpm : TmpPP.macros())
     {
         auto it = MacroPreviouslyEnabled.find(tmpm.first);
         if (it != MacroPreviouslyEnabled.end())
         {
             auto MD = tmpm.second.getLatest();
             auto MI = MD->getMacroInfo();
             if (MI->isEnabled() && !it->second)
             {
                 MI->DisableMacro();
             }
             else if (!MI->isEnabled() && it->second)
             {
                 MI->EnableMacro();
             }
         }
     }

     return out;
}

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