Make --mutation-info-file optional

Make `--mutation-info-file` parameter optional as writing this file can cause issues if
the mutation tree is too deep.

README.md

@@ -72,11 +72,7 @@ We first show how to apply Dredd to a simple stand-alone program. We will then s
 
 ```
 # This will modify pi.cc in-place.
-# The --mutation-info-file argument is used to specify a JSON file to
-# which Dredd will output machine-readable information about the
-# mutations it applied. For the purposes of this example, this file
-# can be ignored.
-${DREDD_EXECUTABLE} examples/simple/pi.cc --mutation-info-file temp.json
+${DREDD_EXECUTABLE} examples/simple/pi.cc
 # Now compile the mutated version of the example
 ${DREDD_CLANG_BIN_DIR}/clang++ examples/simple/pi.cc -o examples/simple/pi
 ```
@@ -98,7 +94,6 @@ You can also enable multiple mutants by setting the environment variable to a co
 To clean up and restore the file `pi.cc` to it's initial state, run
 ```
 rm examples/simple/pi
-rm temp.json
 git checkout HEAD examples/simple/pi.cc
 ```
 
@@ -141,6 +136,10 @@ ${DREDD_EXECUTABLE} -p build math/src/*.cc --mutation-info-file mutant-info.json
 The `-p` option allows the compilation database generated by CMake above to be passed to Dredd: the `compile_commands.json` file in `build` will be used as a compilation database.
 This is so that Dredd knows the correct compiler options to use when processing each source file.
 
+The optional `--mutation-info-file` argument is used to specify a JSON file to which Dredd will output
+machine-readable information about the mutations it applied. We explain how the `mutant-info.json` file created
+via the `--mutation-info-file` argument can be used to query the mutants that Dredd has introduced.
+
 You can run `git status` to see which files have changed, and `git diff` to see
 the effect that Dredd has had on these files. These changes will be hard to understand as they are not intended to be
 readable by humans.

src/dredd/src/main.cc

@@ -14,6 +14,7 @@
 
 #include <fstream>
 #include <memory>
+#include <optional>
 #include <string>
 
 #include "clang/Tooling/CommonOptionsParser.h"
@@ -61,7 +62,7 @@ static llvm::cl::opt<bool> dump_asts(
     llvm::cl::cat(mutate_category));
 // NOLINTNEXTLINE
 static llvm::cl::opt<std::string> mutation_info_file(
-    "mutation-info-file", llvm::cl::Required,
+    "mutation-info-file",
     llvm::cl::desc(
         ".json file into which mutation information should be written"),
     llvm::cl::cat(mutate_category));
@@ -94,7 +95,13 @@ int main(int argc, const char** argv) {
 
   // Keeps track of the mutations that are applied to each source file,
   // including their hierarchical structure.
-  dredd::protobufs::MutationInfo mutation_info;
+  std::optional<dredd::protobufs::MutationInfo> mutation_info;
+
+  if (mutation_info_file.empty()) {
+    mutation_info = std::nullopt;
+  } else {
+    mutation_info = dredd::protobufs::MutationInfo();
+  }
 
   const std::unique_ptr<clang::tooling::FrontendActionFactory> factory =
       dredd::NewMutateFrontendActionFactory(!no_mutation_opts, dump_asts,
@@ -103,15 +110,15 @@ int main(int argc, const char** argv) {
 
   const int return_code = Tool.run(factory.get());
 
-  if (return_code == 0) {
+  if (mutation_info.has_value() && return_code == 0) {
     // Application of mutations was successful, so write out the mutation info
     // in JSON format.
     std::string json_string;
     auto json_options = google::protobuf::util::JsonOptions();
     json_options.add_whitespace = true;
     json_options.always_print_primitive_fields = true;
     auto json_generation_status = google::protobuf::util::MessageToJsonString(
-        mutation_info, &json_string, json_options);
+        mutation_info.value(), &json_string, json_options);
     if (json_generation_status.ok()) {
       std::ofstream transformations_json_file(mutation_info_file);
       transformations_json_file << json_string;

src/libdredd/include/libdredd/new_mutate_frontend_action_factory.h

@@ -16,6 +16,7 @@
 #define LIBDREDD_NEW_MUTATE_FRONTEND_ACTION_FACTORY_H
 
 #include <memory>
+#include <optional>
 
 #include "clang/Tooling/Tooling.h"
 #include "libdredd/protobufs/dredd_protobufs.h"
@@ -26,7 +27,7 @@ std::unique_ptr<clang::tooling::FrontendActionFactory>
 NewMutateFrontendActionFactory(bool optimise_mutations, bool dump_asts,
                                bool only_track_mutant_coverage,
                                int& mutation_id,
-                               protobufs::MutationInfo& mutation_info);
+                               std::optional<protobufs::MutationInfo> &mutation_info);
 
 }  // namespace dredd
 

src/libdredd/include/libdredd/protobufs/dredd.proto

@@ -15,7 +15,10 @@ syntax = "proto3";
 
 package dredd.protobufs;
 
-message MutationInfo { repeated MutationInfoForFile info_for_files = 1; }
+message MutationInfo {
+  repeated MutationInfoForFile info_for_files = 1;
+  bool use = 2;
+}
 
 message MutationInfoForFile {
   string filename = 1;

src/libdredd/include_private/include/libdredd/mutate_ast_consumer.h

@@ -16,6 +16,7 @@
 #define LIBDREDD_MUTATE_AST_CONSUMER_H
 
 #include <memory>
+#include <optional>
 #include <string>
 #include <unordered_set>
 
@@ -34,7 +35,7 @@ class MutateAstConsumer : public clang::ASTConsumer {
   MutateAstConsumer(const clang::CompilerInstance& compiler_instance,
                     bool optimise_mutations, bool dump_ast,
                     bool only_track_mutant_coverage, int& mutation_id,
-                    protobufs::MutationInfo& mutation_info)
+                    std::optional<protobufs::MutationInfo> &mutation_info)
       : compiler_instance_(&compiler_instance),
         optimise_mutations_(optimise_mutations),
         dump_ast_(dump_ast),
@@ -68,7 +69,7 @@ class MutateAstConsumer : public clang::ASTConsumer {
       clang::ASTContext& context,
       protobufs::MutationInfoForFile& protobufs_mutation_info_for_file,
       protobufs::MutationTreeNode& protobufs_mutation_tree_node,
-      std::unordered_set<std::string>& dredd_declarations);
+      std::unordered_set<std::string>& dredd_declarations, bool build_tree);
 
   const clang::CompilerInstance* compiler_instance_;
 
@@ -89,7 +90,7 @@ class MutateAstConsumer : public clang::ASTConsumer {
   // for different translation units.
   int* mutation_id_;
 
-  protobufs::MutationInfo* mutation_info_;
+  std::optional<protobufs::MutationInfo>* mutation_info_;
 };
 
 }  // namespace dredd

src/libdredd/src/mutate_ast_consumer.cc

@@ -83,16 +83,20 @@ void MutateAstConsumer::HandleTranslationUnit(clang::ASTContext& ast_context) {
   std::unordered_set<std::string> dredd_declarations;
 
   protobufs::MutationInfoForFile mutation_info_for_file;
-  mutation_info_for_file.set_filename(
-      ast_context.getSourceManager()
-          .getFileEntryForID(ast_context.getSourceManager().getMainFileID())
-          ->getName()
-          .str());
+
+  if (mutation_info_->has_value()) {
+    mutation_info_for_file.set_filename(
+        ast_context.getSourceManager()
+            .getFileEntryForID(ast_context.getSourceManager().getMainFileID())
+            ->getName()
+            .str());
+  }
+
   protobufs::MutationTreeNode* root_protobuf_mutation_tree_node =
       mutation_info_for_file.add_mutation_tree();
   ApplyMutations(visitor_->GetMutations(), initial_mutation_id, ast_context,
                  mutation_info_for_file, *root_protobuf_mutation_tree_node,
-                 dredd_declarations);
+                 dredd_declarations, mutation_info_->has_value());
 
   if (initial_mutation_id == *mutation_id_) {
     // No possibilities for mutation were found; nothing else to do.
@@ -135,7 +139,9 @@ void MutateAstConsumer::HandleTranslationUnit(clang::ASTContext& ast_context) {
     }
   }
 
-  *mutation_info_->add_info_for_files() = mutation_info_for_file;
+  if (mutation_info_->has_value()) {
+    *mutation_info_->value().add_info_for_files() = mutation_info_for_file;
+  }
 
   auto& source_manager = ast_context.getSourceManager();
   const clang::SourceLocation start_of_source_file =
@@ -411,7 +417,7 @@ void MutateAstConsumer::ApplyMutations(
     clang::ASTContext& context,
     protobufs::MutationInfoForFile& protobufs_mutation_info_for_file,
     protobufs::MutationTreeNode& protobufs_mutation_tree_node,
-    std::unordered_set<std::string>& dredd_declarations) {
+    std::unordered_set<std::string>& dredd_declarations, bool build_tree) {
   assert(!(dredd_mutation_tree_node.IsEmpty() &&
            dredd_mutation_tree_node.GetChildren().size() == 1) &&
          "The mutation tree should already be compressed.");
@@ -422,17 +428,18 @@ void MutateAstConsumer::ApplyMutations(
         protobufs_mutation_info_for_file.mutation_tree_size()));
     protobufs::MutationTreeNode* new_protobufs_mutation_tree_node =
         protobufs_mutation_info_for_file.add_mutation_tree();
-    ApplyMutations(*child, initial_mutation_id, context,
-                   protobufs_mutation_info_for_file,
-                   *new_protobufs_mutation_tree_node, dredd_declarations);
+    ApplyMutations(
+        *child, initial_mutation_id, context, protobufs_mutation_info_for_file,
+        *new_protobufs_mutation_tree_node, dredd_declarations, build_tree);
   }
+
   for (const auto& mutation : dredd_mutation_tree_node.GetMutations()) {
     const int mutation_id_old = *mutation_id_;
     const auto mutation_group = mutation->Apply(
         context, compiler_instance_->getPreprocessor(), optimise_mutations_,
         only_track_mutant_coverage_, initial_mutation_id, *mutation_id_,
         rewriter_, dredd_declarations);
-    if (*mutation_id_ > mutation_id_old) {
+    if (build_tree && *mutation_id_ > mutation_id_old) {
       // Only add the result of applying the mutation if it had an effect.
       *protobufs_mutation_tree_node.add_mutation_groups() = mutation_group;
     }

src/libdredd/src/new_mutate_frontend_action_factory.cc

@@ -33,7 +33,7 @@ class MutateFrontendAction : public clang::ASTFrontendAction {
  public:
   MutateFrontendAction(bool optimise_mutations, bool dump_asts,
                        bool only_track_mutant_coverage, int& mutation_id,
-                       protobufs::MutationInfo& mutation_info,
+                       std::optional<protobufs::MutationInfo> &mutation_info,
                        std::set<std::string>& processed_files)
       : optimise_mutations_(optimise_mutations),
         dump_asts_(dump_asts),
@@ -65,22 +65,22 @@ class MutateFrontendAction : public clang::ASTFrontendAction {
   bool dump_asts_;
   bool only_track_mutant_coverage_;
   int* mutation_id_;
-  protobufs::MutationInfo* mutation_info_;
+  std::optional<protobufs::MutationInfo>* mutation_info_;
   std::set<std::string>* processed_files_;
 };
 
 std::unique_ptr<clang::tooling::FrontendActionFactory>
 NewMutateFrontendActionFactory(bool optimise_mutations, bool dump_asts,
                                bool only_track_mutant_coverage,
                                int& mutation_id,
-                               protobufs::MutationInfo& mutation_info) {
+                               std::optional<protobufs::MutationInfo> &mutation_info) {
   class MutateFrontendActionFactory
       : public clang::tooling::FrontendActionFactory {
    public:
     MutateFrontendActionFactory(bool optimise_mutations, bool dump_asts,
                                 bool only_track_mutant_coverage,
                                 int& mutation_id,
-                                protobufs::MutationInfo& mutation_info)
+                                std::optional<protobufs::MutationInfo> &mutation_info)
         : optimise_mutations_(optimise_mutations),
           dump_asts_(dump_asts),
           only_track_mutant_coverage_(only_track_mutant_coverage),
@@ -98,7 +98,7 @@ NewMutateFrontendActionFactory(bool optimise_mutations, bool dump_asts,
     bool dump_asts_;
     bool only_track_mutant_coverage_;
     int* mutation_id_;
-    protobufs::MutationInfo* mutation_info_;
+    std::optional<protobufs::MutationInfo>* mutation_info_;
 
     // Stores the ids of the files that have been processed so far, to avoid
     // processing a file multiple times.