Teach history search to move forward in time

Will use this for forward incremental search.

No functional change.

src/fish_tests.cpp

@@ -3793,7 +3793,7 @@ static void test_autosuggestion_combining() {
 static void test_history_matches(history_search_t &search, const wcstring_list_t &expected,
                                  unsigned from_line) {
     wcstring_list_t found;
-    while (search.go_backwards()) {
+    while (search.go_to_next_match(history_search_direction_t::backward)) {
         found.push_back(search.current_string());
     }
     do_test_from(expected == found, from_line);

src/history.cpp

@@ -627,14 +627,24 @@ void history_impl_t::load_old_if_needed() {
     }
 }
 
-bool history_search_t::go_backwards() {
+bool history_search_t::go_to_next_match(history_search_direction_t direction) {
     // Backwards means increasing our index.
-    const auto max_index = static_cast<size_t>(-1);
+    size_t invalid_index;
+    ssize_t increment;
 
-    if (current_index_ == max_index) return false;
+    if (direction == history_search_direction_t::backward) {
+        invalid_index = static_cast<size_t>(-1);
+        increment = 1;
+    } else {
+        assert(direction == history_search_direction_t::forward);
+        invalid_index = 0;
+        increment = -1;
+    }
+
+    if (current_index_ == invalid_index) return false;
 
     size_t index = current_index_;
-    while (++index < max_index) {
+    while ((index += increment) != invalid_index) {
         history_item_t item = history_->item_at_index(index);
 
         // We're done if it's empty or we cancelled.
@@ -1460,7 +1470,7 @@ static void do_1_history_search(history_t *hist, history_search_type_t search_ty
                                 const cancel_checker_t &cancel_check) {
     history_search_t searcher = history_search_t(hist, search_string, search_type,
                                                  case_sensitive ? 0 : history_search_ignore_case);
-    while (!cancel_check() && searcher.go_backwards()) {
+    while (!cancel_check() && searcher.go_to_next_match(history_search_direction_t::backward)) {
         if (!func(searcher.current_item())) {
             break;
         }

src/history.h

@@ -129,6 +129,8 @@ using history_item_list_t = std::deque<history_item_t>;
 
 struct history_impl_t;
 
+enum class history_search_direction_t { forward, backward };
+
 class history_t : noncopyable_t, nonmovable_t {
     friend class history_tests_t;
     struct impl_wrapper_t;
@@ -269,8 +271,8 @@ class history_search_t {
     /// Gets the original search term.
     const wcstring &original_term() const { return orig_term_; }
 
-    /// Finds the previous search result (backwards in time). Returns true if one was found.
-    bool go_backwards();
+    // Finds the next search result. Returns true if one was found.
+    bool go_to_next_match(history_search_direction_t direction);
 
     /// Returns the current search result item. asserts if there is no current item.
     const history_item_t &current_item() const;

src/reader.cpp

@@ -123,8 +123,6 @@ static const size_t TAB_COMPLETE_WILDCARD_MAX_EXPANSION = 256;
 /// current contents of the kill buffer.
 #define KILL_PREPEND 1
 
-enum class history_search_direction_t { forward, backward };
-
 enum class jump_direction_t { forward, backward };
 enum class jump_precision_t { till, to };
 
@@ -445,7 +443,7 @@ class reader_history_search_t {
         }
 
         // Add more items from our search.
-        while (search_.go_backwards()) {
+        while (search_.go_to_next_match(history_search_direction_t::backward)) {
             if (append_matches_from_search()) {
                 match_index_++;
                 assert(match_index_ < matches_.size() && "Should have found more matches");
@@ -1242,7 +1240,8 @@ static history_pager_result_t history_pager_search(const std::shared_ptr<history
     completion_list_t completions;
     history_search_t search{history, search_string, history_search_type_t::contains,
                             smartcase_flags(search_string)};
-    while (completions.size() < page_size && search.go_backwards()) {
+    while (completions.size() < page_size &&
+           search.go_to_next_match(history_search_direction_t::backward)) {
         const history_item_t &item = search.current_item();
         completions.push_back(completion_t{
             item.str(), L"", string_fuzzy_match_t::exact_match(),
@@ -1841,7 +1840,8 @@ static std::function<autosuggestion_t(void)> get_autosuggestion_performer(
         // Search history for a matching item.
         history_search_t searcher(history.get(), search_string, history_search_type_t::prefix,
                                   history_search_flags_t{});
-        while (!ctx.check_cancel() && searcher.go_backwards()) {
+        while (!ctx.check_cancel() &&
+               searcher.go_to_next_match(history_search_direction_t::backward)) {
             const history_item_t &item = searcher.current_item();
 
             // Skip items with newlines because they make terrible autosuggestions.