// file : libbuild2/config/utility.txx -*- C++ -*- // license : MIT; see accompanying LICENSE file namespace build2 { namespace config { template <typename T> pair<lookup, bool> lookup_config_impl (scope& rs, const variable& var, T&& def_val, uint64_t sflags, bool def_ovr) { // Note: see also the other lookup_config() implementation if changing // anything here. save_variable (rs, var, sflags); pair<lookup, size_t> org (rs.lookup_original (var)); bool n (false); // New flag. lookup l (org.first); // The interaction with command line overrides can get tricky. For // example, the override to default value could make (non-recursive) // command line override in the outer scope no longer apply. So what we // are going to do is first ignore overrides and perform the normal // logic on the original. Then we apply the overrides on the result. // // Note that this is not exactly the "lookup and set to default if // undefined" semantics in case there is no original but there is an // override. In this case we will set original to default and then apply // the override, which could be append or non-recursive (as mentioned // above). It does, however, feel like taking into account the default // in such cases is the correct semantics since append is meant as an // addition to something existing and non-recursive override is only // meant to override at the level it was specified. Though it won't be // surprising at all if we end up with some counter-intuitive behavior // here. // // Actually, the above analysis is not the full picture: if we have one // of those overrides (append, non-recursive) in the outer project, then // the lookup_config() call at that level will set the corresponding // variable on that scope and we will see it as "original-defined" from // our scope. Of course if there is no call to lookup_config() for this // variable in the outer scope, then we won't see anything but then our // behavior in this case seems correct: since that value is not part of // the configuration (and won't be saved), then we should stick to our // default. In other words, we should only inherit the value if it is // actually recognized as a configuration value by the outer project. // // So, to summarize the current understanding, while our semantics is // not exactly "lookup and set to default if undefined" in some obscure // corner cases, it seem to be the correct/preferred one. // if (!l.defined () || (def_ovr && !l.belongs (rs))) { value& v (rs.assign (var) = std::forward<T> (def_val)); // VC14 v.extra = 1; // Default value flag. n = (sflags & save_default_commented) == 0; // Absence means default. l = lookup (v, var, rs); org = make_pair (l, 1); // Lookup depth is 1 since it's in rs.vars. } // Treat an inherited value that was set to default as new. // else if (l->extra == 1) n = (sflags & save_default_commented) == 0; // Absence means default. if (var.overrides != nullptr) { pair<lookup, size_t> ovr (rs.lookup_override (var, move (org))); if (l != ovr.first) // Overriden? { // Override is always treated as new. // n = true; l = move (ovr.first); } } return pair<lookup, bool> (l, n); } } }