Include subsequence matches in history-pager

If a `contains` search yields no results, try again with `contains_subsequence`.

src/history.cpp

@@ -195,6 +195,9 @@ bool history_item_t::matches_search(const wcstring &term, enum history_search_ty
             if (wcpattern2.back() != ANY_STRING) wcpattern2.push_back(ANY_STRING);
             return wildcard_match(content_to_match, wcpattern2);
         }
+        case history_search_type_t::contains_subsequence: {
+            return subsequence_in_string(term, content_to_match);
+        }
         case history_search_type_t::match_everything: {
             return true;
         }

src/history.h

@@ -57,6 +57,8 @@ enum class history_search_type_t {
     contains_glob,
     /// Search for commands starting with the given glob pattern.
     prefix_glob,
+    /// Search for commands containing the given string as a subsequence
+    contains_subsequence,
     /// Matches everything.
     match_everything,
 };

src/reader.cpp

@@ -1288,11 +1288,21 @@ 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), history_index};
-    while (completions.size() < page_size && search.go_to_next_match(direction)) {
+    bool next_match_found = search.go_to_next_match(direction);
+    if (!next_match_found) {
+        // If there were no matches, try again with subsequence search
+        search =
+            history_search_t{history, search_string, history_search_type_t::contains_subsequence,
+                             smartcase_flags(search_string), history_index};
+        next_match_found = search.go_to_next_match(direction);
+    }
+    while (completions.size() < page_size && next_match_found) {
         const history_item_t &item = search.current_item();
         completions.push_back(completion_t{
             item.str(), L"", string_fuzzy_match_t::exact_match(),
             COMPLETE_REPLACES_COMMANDLINE | COMPLETE_DONT_ESCAPE | COMPLETE_DONT_SORT});
+
+        next_match_found = search.go_to_next_match(direction);
     }
     size_t last_index = search.current_index();
     if (direction == history_search_direction_t::forward)

src/wcstringutil.cpp

@@ -119,7 +119,7 @@ bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
 
 /// Returns true if needle, represented as a subsequence, is contained within haystack.
 /// Note subsequence is not substring: "foo" is a subsequence of "follow" for example.
-static bool subsequence_in_string(const wcstring &needle, const wcstring &haystack) {
+bool subsequence_in_string(const wcstring &needle, const wcstring &haystack) {
     // Impossible if needle is larger than haystack.
     if (needle.size() > haystack.size()) {
         return false;

src/wcstringutil.h

@@ -34,6 +34,9 @@ bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
 bool string_prefixes_string_case_insensitive(const wcstring &proposed_prefix,
                                              const wcstring &value);
 
+/// Test if a string matches a subsequence of another.
+bool subsequence_in_string(const wcstring &needle, const wcstring &haystack);
+
 /// Case-insensitive string search, modeled after std::string::find().
 /// \param fuzzy indicates this is being used for fuzzy matching and case insensitivity is
 /// expanded to include symbolic characters (#3584).