Remove free/member functions from C++ source code via clang AST manipulation, leaving only types/structs/etc behind, then print the modified source

clang_ast_remove_functions.cpp

#define _SILENCE_CXX17_ITERATOR_BASE_CLASS_DEPRECATION_WARNING
#include <clang/AST/AST.h>
#include <clang/AST/ASTConsumer.h>
#include <clang/AST/RecursiveASTVisitor.h>
#include <clang/Frontend/CompilerInstance.h>
#include <clang/Frontend/FrontendAction.h>
#include <clang/Tooling/Tooling.h>
#undef _SILENCE_CXX17_ITERATOR_BASE_CLASS_DEPRECATION_WARNING

#include <fstream>
#include <utility>

using namespace clang;

namespace {
class RemoveFunctionsConsumer : public ASTConsumer {
public:
    void HandleTranslationUnit(ASTContext &context) override {
        auto translation_unit = context.getTranslationUnitDecl();

        struct Visitor : public RecursiveASTVisitor<Visitor> {
            static bool VisitFunctionDecl(FunctionDecl *decl) {
                // remove any free functions (or member functions that have been defined outside the class)
                decl->getLexicalParent()->removeDecl(decl);
                return true;
            }

            static bool VisitCXXRecordDecl(CXXRecordDecl *decl) {
                // remove all methods/constructors/etc from a class/struct
                auto methods = std::vector(decl->method_begin(), decl->method_end());
                for (auto method : methods) {
                    decl->removeDecl(method);
                }
                return true;
            }
        };

        Visitor().TraverseDecl(translation_unit);
        // print the modified translation unit
        translation_unit->print(llvm::outs());
    }
};

class RemoveFunctionsAction : public PluginASTAction {
protected:
    std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance&, llvm::StringRef) override {
        return std::make_unique<RemoveFunctionsConsumer>();
    }

    bool ParseArgs(const CompilerInstance &, const std::vector<std::string> &args) override {
        return true;
    }
};

std::vector<char> read_file_bytes(const char *filename) {
    std::ifstream infile(filename);

    infile.seekg(0, std::ios_base::end);
    auto file_size = static_cast<size_t>(infile.tellg());
    infile.seekg(0, std::ios_base::beg);

    // note: add one to size so code.data() is a null terminated string
    std::vector<char> code;
    code.resize(file_size + 1, '\0');
    infile.read(code.data(), file_size);

    return code;
}

} // namespace

int main(int argc, char *argv[]) {
    if (argc == 2) {
        auto code = read_file_bytes(argv[1]);
        auto tool = std::make_unique<RemoveFunctionsAction>();

        if (clang::tooling::runToolOnCode(std::move(tool), code.data())) {
            return 0;
        } else {
            return 2;
        }
    } else {
        return 1;
    }
}