sec

    // Explicit rule has no recipe - try pattern/implicit rules for recipe

    const Rule* pattern = mf_.find_pattern_rule(target, stem);

    if (pattern) return pattern;

    if (pattern) {

        // GNU make only applies an implicit rule when its prerequisites exist

        // or can themselves be made. Without this check a self-similar pattern

        // such as "x/%: x/%_shipped" would chain forever (x/ -> x/_shipped ->

        // x/_shipped_shipped -> ...), growing the target name until the process

        // runs out of memory. A prerequisite counts as satisfiable if the file

        // exists, an explicit rule produces it, or it is phony.

        bool viable = true;

        for (const auto& p : pattern->prerequisites) {

            std::string prereq = p;

            size_t ppct = prereq.find('%');

            if (ppct != std::string::npos) {

                prereq = prereq.substr(0, ppct) + stem + prereq.substr(ppct + 1);

            }

            prereq = parser_.expand(prereq, mf_);

            if (prereq.empty()) continue;

            if (file_exists(prereq)) continue;

            if (mf_.find_explicit_rule(prereq)) continue;

            if (mf_.phony_targets.count(prereq)) continue;

            viable = false;

            break;

        }

        if (viable) return pattern;

    }

    // Built-in implicit rules

    static std::vector<Rule> builtins;