Modifying clang AST using a plugin - clang

Question

I would like to modify the clang AST using a plugin.
I have following the suggestions of using Clang Rewriter object.
I use compiler.createDefaultOutputFile() to obtain the output stream to write the changed file into it.
the compilation works fine but the generated object file is broken.
I get the following linker error: "File format not recognized".
Build command line:
clang++-8 -Xclang -load -Xclang libcashpp.so -Xclang -add-plugin -Xclang cash-pp test.cpp
Build Output:
/tmp/test-eb7d3d.o: file not recognized: File format not recognized
Question:
Is it actually possible to update the AST using a clang plugin?
Can someone point me to an example program that does that?
Source Code:
#include <clang/Frontend/FrontendPluginRegistry.h>
#include <clang/AST/AST.h>
#include <clang/AST/ASTConsumer.h>
#include <clang/AST/RecursiveASTVisitor.h>
#include "clang/Rewrite/Core/Rewriter.h"
#include <clang/Frontend/CompilerInstance.h>
#include <clang/Sema/Sema.h>
#include <llvm/Support/raw_ostream.h>
#include <string>
#include <sstream>
namespace {
class VarDeclVisitor : public clang::RecursiveASTVisitor<VarDeclVisitor> {
public:
VarDeclVisitor(clang::Rewriter& rewriter)
: rewriter_(rewriter)
{}
bool VisitCallExpr(clang::CallExpr *ce) {
auto q = ce->getType();
auto t = q.getTypePtrOrNull();
if (t != NULL) {
auto callee = ce->getDirectCallee();
auto funcName = callee->getNameInfo().getAsString();
if (funcName == "getInstanceName") {
rewriter_.ReplaceText(ce->getBeginLoc(), callee->getIdentifier()->getName().size(), "getInstanceName2");
}
}
return true;
}
private:
clang::Rewriter& rewriter_;
};
class MyASTConsumer : public clang::ASTConsumer {
using Base = clang::ASTConsumer;
public:
MyASTConsumer(std::unique_ptr<llvm::raw_pwrite_stream>&& os)
: os_(std::move(os))
{}
void HandleTranslationUnit(clang::ASTContext &context) override {
clang::Rewriter rewriter(context.getSourceManager(), context.getLangOpts());
VarDeclVisitor visitor(rewriter);
auto &source_manager = context.getSourceManager();
const auto &mainFileID = source_manager.getMainFileID();
const auto &decls = context.getTranslationUnitDecl()->decls();
for (auto &decl : decls) {
const auto &fileID = source_manager.getFileID(decl->getLocation());
if (fileID != mainFileID)
continue;
visitor.TraverseDecl(decl);
}
auto rwbuf = rewriter.getRewriteBufferFor(mainFileID);
if (rwbuf) {
*os_ << std::string(rwbuf->begin(), rwbuf->end());
} else {
*os_ << source_manager.getBufferData(mainFileID);
}
}
private:
std::unique_ptr<llvm::raw_pwrite_stream> os_;
};
class MyPlugin : public clang::PluginASTAction {
public:
std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(clang::CompilerInstance &compiler,
llvm::StringRef inFile) override {
auto os = compiler.createDefaultOutputFile(false, inFile, "cpp");
if (!os)
return nullptr;
return std::make_unique<MyASTConsumer>(std::move(os));
}
bool ParseArgs(const clang::CompilerInstance &compiler,
const std::vector<std::string> &args) override {
return true;
}
void PrintHelp(llvm::raw_ostream &ros) {}
};
}
static clang::FrontendPluginRegistry::Add<MyPlugin>
X("cash-pp", "My plugin");