1 files changed, 128 insertions, 0 deletions
diff --git a/bpkg/package-configuration.cxx b/bpkg/package-configuration.cxx
new file mode 100644
index 0000000..fb742e8
--- /dev/null
+++ b/bpkg/package-configuration.cxx
@@ -0,0 +1,128 @@
+// file      : bpkg/package-configuration.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <bpkg/package-configuration.hxx>
+
+#include <bpkg/package-skeleton.hxx>
+
+namespace bpkg
+{
+  using build2::config::variable_origin;
+
+  bool
+  up_negotiate_configuration (
+    package_configurations& cfgs,
+    package_skeleton& dept,
+    pair<size_t, size_t> pos,
+    const small_vector<reference_wrapper<package_skeleton>, 1>& depcs)
+  {
+    dependent_config_variable_values old_cfgs;
+
+    // Step 1: save a snapshot of the old configuration while unsetting values
+    // that have this dependent as the originator and reloading the defaults.
+    //
+    // While at it, also collect the configurations to pass to dependent's
+    // evaluate_*() calls.
+    //
+    package_skeleton::dependency_configurations depc_cfgs;
+    depc_cfgs.reserve (depcs.size ());
+
+    for (package_skeleton& depc: depcs)
+    {
+      package_configuration& cfg (cfgs[depc.key]);
+
+      for (config_variable_value& v: cfg)
+      {
+        if (v.origin == variable_origin::buildfile)
+        {
+          if (*v.dependent == dept.key)
+          {
+            old_cfgs.push_back (
+              dependent_config_variable_value {
+                v.name, move (v.value), move (*v.dependent)});
+
+            v.origin = variable_origin::undefined;
+            v.dependent = nullopt;
+          }
+          else
+            old_cfgs.push_back (
+              dependent_config_variable_value {v.name, v.value, *v.dependent});
+        }
+      }
+
+      depc.reload_defaults (cfg);
+
+      depc_cfgs.push_back (cfg);
+    }
+
+    // Step 2: execute the prefer/accept or requires clauses.
+    //
+    pos.first--; pos.second--; // Convert to 0-base.
+
+    const dependency_alternative& da (
+      dept.available.get ().dependencies[pos.first][pos.second]);
+
+    if (!(da.require
+          ? dept.evaluate_require (depc_cfgs, *da.require, pos.first)
+          : dept.evaluate_prefer_accept (depc_cfgs,
+                                         *da.prefer, *da.accept, pos.first)))
+    {
+      fail << "unable to negotiate acceptable configuration"; // @@ TODO
+    }
+
+    // Check if anything changed by comparing to entries in old_cfgs.
+    //
+    {
+      optional<size_t> n (0); // Number of unchanged.
+
+      for (package_skeleton& depc: depcs)
+      {
+        package_configuration& cfg (cfgs[depc.key]);
+
+        for (config_variable_value& v: cfg)
+        {
+          if (v.origin == variable_origin::buildfile)
+          {
+            auto i (find_if (old_cfgs.begin (), old_cfgs.end (),
+                             [&v] (const dependent_config_variable_value& o)
+                             {
+                               return v.name == o.name;
+                             }));
+
+            if (i == old_cfgs.end () ||
+                i->value != v.value  ||
+                i->dependent != *v.dependent)
+            {
+              n = nullopt;
+              break;
+            }
+
+            ++*n;
+          }
+        }
+
+        if (!n)
+          break;
+      }
+
+      // If we haven't seen any changed and we've seen the same number, then
+      // nothing has changed.
+      //
+      if (n && *n == old_cfgs.size ())
+        return false;
+    }
+
+
+    // @@ TODO: look for cycles in change history.
+    // @@ TODO: save in change history.
+    //
+    /*
+    dependent_config_variable_values new_cfgs; // @@ TODO.
+
+    old_cfgs.sort ();
+    new_cfgs.sort ();
+    */
+
+    return true;
+  }
+}