[issue1112] Add flag -Wzero-as-null-pointer-constant and fix resulting warnings.

src/cmake_modules/FastDownwardMacros.cmake

@@ -18,7 +18,7 @@ macro(fast_downward_set_compiler_flags)
         check_and_set_compiler_flag( "-std=c++20" )
 
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g")
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpedantic -Wnon-virtual-dtor -Wfloat-conversion -Wmissing-declarations")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpedantic -Wnon-virtual-dtor -Wfloat-conversion -Wmissing-declarations -Wzero-as-null-pointer-constant")
 
         if (CMAKE_COMPILER_IS_GNUCXX
             AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 12

src/search/heuristics/cea_heuristic.cc

@@ -98,7 +98,7 @@ struct LocalProblemNode {
           cost(-1),
           expanded(false),
           context(context_size, -1),
-          reached_by(0) {
+          reached_by(nullptr) {
     }
 
     ~LocalProblemNode() {
@@ -222,7 +222,7 @@ void ContextEnhancedAdditiveHeuristic::set_up_local_problem(
         to_node.expanded = false;
         to_node.cost = numeric_limits<int>::max();
         to_node.waiting_list.clear();
-        to_node.reached_by = 0;
+        to_node.reached_by = nullptr;
     }
 
     LocalProblemNode *start = &problem->nodes[start_value];
@@ -359,7 +359,7 @@ void ContextEnhancedAdditiveHeuristic::mark_helpful_transitions(
     assert(node->cost >= 0 && node->cost < numeric_limits<int>::max());
     LocalTransition *first_on_path = node->reached_by;
     if (first_on_path) {
-        node->reached_by = 0; // Clear to avoid revisiting this node later.
+        node->reached_by = nullptr; // Clear to avoid revisiting this node later.
         if (first_on_path->target_cost == first_on_path->action_cost) {
             // Transition possibly applicable.
             const ValueTransitionLabel &label = *first_on_path->label;
@@ -425,7 +425,7 @@ ContextEnhancedAdditiveHeuristic::ContextEnhancedAdditiveHeuristic(
     VariablesProxy vars = task_proxy.get_variables();
     local_problem_index.resize(vars.size());
     for (VariableProxy var : vars)
-        local_problem_index[var.get_id()].resize(var.get_domain_size(), 0);
+        local_problem_index[var.get_id()].resize(var.get_domain_size(), nullptr);
 }
 
 ContextEnhancedAdditiveHeuristic::~ContextEnhancedAdditiveHeuristic() {

src/search/heuristics/cg_heuristic.cc

@@ -105,10 +105,10 @@ int CGHeuristic::get_transition_cost(const State &state,
     if (start->distances.empty()) {
         // Initialize data of initial node.
         start->distances.resize(dtg->nodes.size(), numeric_limits<int>::max());
-        start->helpful_transitions.resize(dtg->nodes.size(), 0);
+        start->helpful_transitions.resize(dtg->nodes.size(), nullptr);
         start->distances[start_val] = 0;
-        start->reached_from = 0;
-        start->reached_by = 0;
+        start->reached_from = nullptr;
+        start->reached_by = nullptr;
         start->children_state.resize(dtg->local_to_global_child.size());
         for (size_t i = 0; i < dtg->local_to_global_child.size(); ++i) {
             start->children_state[i] =
@@ -188,7 +188,7 @@ int CGHeuristic::get_transition_cost(const State &state,
                         target->reached_from = source;
                         target->reached_by = &label;
 
-                        if (current_helpful_transition == 0) {
+                        if (current_helpful_transition == nullptr) {
                             // This transition starts at the start node;
                             // no helpful transitions recorded yet.
                             start->helpful_transitions[target->value] = &label;

src/search/heuristics/domain_transition_graph.h

@@ -111,7 +111,8 @@ struct ValueNode {
     ValueTransitionLabel *reached_by;
 
     ValueNode(DomainTransitionGraph *parent, int val)
-        : parent_graph(parent), value(val), reached_from(0), reached_by(0) {}
+        : parent_graph(parent), value(val), reached_from(nullptr),
+          reached_by(nullptr) {}
 };
 
 class DomainTransitionGraph {

src/search/heuristics/lm_cut_landmarks.cc

@@ -102,7 +102,7 @@ void LandmarkCutLandmarks::setup_exploration_queue() {
 
     for (RelaxedOperator &op : relaxed_operators) {
         op.unsatisfied_preconditions = op.preconditions.size();
-        op.h_max_supporter = 0;
+        op.h_max_supporter = nullptr;
         op.h_max_supporter_cost = numeric_limits<int>::max();
     }
 }

src/search/landmarks/landmark_factory_merged.cc

@@ -24,18 +24,18 @@ LandmarkNode *LandmarkFactoryMerged::get_matching_landmark(const Landmark &landm
         if (lm_graph->contains_simple_landmark(lm_fact))
             return &lm_graph->get_simple_landmark(lm_fact);
         else
-            return 0;
+            return nullptr;
     } else if (landmark.disjunctive) {
         set<FactPair> lm_facts(landmark.facts.begin(), landmark.facts.end());
         if (lm_graph->contains_identical_disjunctive_landmark(lm_facts))
             return &lm_graph->get_disjunctive_landmark(landmark.facts[0]);
         else
-            return 0;
+            return nullptr;
     } else if (landmark.conjunctive) {
         cerr << "Don't know how to handle conjunctive landmarks yet" << endl;
         utils::exit_with(ExitCode::SEARCH_UNSUPPORTED);
     }
-    return 0;
+    return nullptr;
 }
 
 void LandmarkFactoryMerged::generate_landmarks(

src/search/lp/soplex_solver_interface.h

@@ -8,6 +8,7 @@
 #ifdef __GNUG__
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wunused-parameter"
+#pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
 #if (__GNUG__ >= 11) || (__clang_major__ >= 12)
 #pragma GCC diagnostic ignored "-Wdeprecated-enum-enum-conversion"
 #endif

src/search/pdbs/match_tree.cc

@@ -78,7 +78,7 @@ MatchTree::~MatchTree() {
 void MatchTree::insert_recursive(
     int op_id, const vector<FactPair> &regression_preconditions,
     int pre_index, Node **edge_from_parent) {
-    if (*edge_from_parent == 0) {
+    if (*edge_from_parent == nullptr) {
         // We don't exist yet: create a new node.
         *edge_from_parent = new Node();
     }
@@ -111,7 +111,7 @@ void MatchTree::insert_recursive(
 
         /* Set up edge to the correct child (for which we want to call
            this function recursively). */
-        Node **edge_to_child = 0;
+        Node **edge_to_child = nullptr;
         if (node->var_id == fact.var) {
             // Operator has a precondition on the variable tested by node.
             edge_to_child = &node->successors[fact.value];

src/search/pdbs/pattern_collection_generator_hillclimbing.cc

@@ -121,7 +121,7 @@ PatternCollectionGeneratorHillclimbing::PatternCollectionGeneratorHillclimbing(c
       max_time(opts.get<double>("max_time")),
       rng(utils::parse_rng_from_options(opts)),
       num_rejected(0),
-      hill_climbing_timer(0) {
+      hill_climbing_timer(nullptr) {
 }
 
 int PatternCollectionGeneratorHillclimbing::generate_candidate_pdbs(

src/search/utils/system_unix.cc

@@ -227,7 +227,7 @@ void register_event_handlers() {
     // On exit or when receiving certain signals such as SIGINT (Ctrl-C),
     // print the peak memory usage.
 #if OPERATING_SYSTEM == LINUX
-    on_exit(exit_handler, 0);
+    on_exit(exit_handler, nullptr);
 #elif OPERATING_SYSTEM == OSX
     atexit(exit_handler);
 #endif
@@ -243,11 +243,11 @@ void register_event_handlers() {
     // Reset handler to default action after completion.
     default_signal_action.sa_flags = SA_RESETHAND;
 
-    sigaction(SIGABRT, &default_signal_action, 0);
-    sigaction(SIGTERM, &default_signal_action, 0);
-    sigaction(SIGSEGV, &default_signal_action, 0);
-    sigaction(SIGINT, &default_signal_action, 0);
-    sigaction(SIGXCPU, &default_signal_action, 0);
+    sigaction(SIGABRT, &default_signal_action, nullptr);
+    sigaction(SIGTERM, &default_signal_action, nullptr);
+    sigaction(SIGSEGV, &default_signal_action, nullptr);
+    sigaction(SIGINT, &default_signal_action, nullptr);
+    sigaction(SIGXCPU, &default_signal_action, nullptr);
 }
 
 void report_exit_code_reentrant(ExitCode exitcode) {