1 files changed, 109 insertions, 13 deletions

diff --git a/mod/build-config.cxx b/mod/build-config.cxx
index e838a59..5d3f46b 100644
--- a/mod/build-config.cxx
+++ b/mod/build-config.cxx
@@ -6,9 +6,10 @@
 
 #include <map>
 #include <sstream>
+#include <algorithm> // find()
 
 #include <libbutl/sha256.mxx>
-#include <libbutl/utility.mxx>    // throw_generic_error()
+#include <libbutl/utility.mxx>    // throw_generic_error(), alpha(), etc.
 #include <libbutl/openssl.mxx>
 #include <libbutl/filesystem.mxx>
 
@@ -150,21 +151,116 @@ namespace brep
   }
 
   bool
-  match (const string& config_pattern,
-         const optional<string>& target_pattern,
-         const build_config& c)
+  exclude (const build_class_exprs& exprs,
+           const build_constraints& constrs,
+           const build_config& cfg,
+           string* reason)
   {
-    return path_match (config_pattern, c.name) &&
-      (!target_pattern || path_match (*target_pattern, c.target.string ()));
-  }
+    // Save the first sentence of the reason, lower-case the first letter if
+    // the beginning looks like a word (the second character is the
+    // lower-case letter or space).
+    //
+    auto sanitize = [] (const string& reason)
+    {
+      string r (reason.substr (0, reason.find ('.')));
 
-  bool
-  exclude (const build_package& p, const build_config& c)
-  {
-    for (const auto& bc: p.constraints)
+      char c;
+      size_t n (r.size ());
+
+      if (n > 0            &&
+          alpha (c = r[0]) &&
+          c == ucase (c)   &&
+          (n == 1 || (alpha (c = r[1]) && c == lcase (c)) || c == ' '))
+        r[0] = lcase (r[0]);
+
+      return r;
+    };
+
+    bool r (false);
+
+    // First, match the configuration against the package underlying build
+    // class set and expressions.
+    //
+    // Determine the underlying class set. Note that in the future we can
+    // potentially extend the underlying set with the special classes.
+    //
+    build_class_expr ucs (
+      !exprs.empty () && !exprs.front ().underlying_classes.empty ()
+      ? exprs.front ()
+      : build_class_expr ("default", "Default"));
+
+    // Transform the combined package build configuration class expression,
+    // making the underlying class set a starting set for the original
+    // expression and a restricting set, simultaneously. For example, for the
+    // expression:
+    //
+    // default legacy : -msvc
+    //
+    // the resulting expression will be:
+    //
+    // +default +legacy -msvc &( +default +legacy )
+    //
+    //
+    build_class_exprs es;
+    es.emplace_back (ucs.underlying_classes, '+', ucs.comment);
+    es.insert       (es.end (), exprs.begin (), exprs.end ());
+    es.emplace_back (ucs.underlying_classes, '&', ucs.comment);
+
+    // We will use a comment of the first encountered excluding expression
+    // (changing the result from true to false) or non-including one (leaving
+    // the false result) as an exclusion reason.
+    //
+    for (const build_class_expr& e: es)
+    {
+      bool pr (r);
+      e.match (cfg.classes, r);
+
+      if (reason != nullptr)
+      {
+        // Reset the reason which, if saved, makes no sense anymore.
+        //
+        if (r)
+        {
+          reason->clear ();
+        }
+        else if (reason->empty () &&
+                 //
+                 // Exclusion.
+                 //
+                 (pr              ||
+                  //
+                  // Non-inclusion. Make sure that the build class expression
+                  // is empty or starts with an addition (+...).
+                  //
+                  e.expr.empty () ||
+                  e.expr.front ().operation == '+'))
+        {
+          *reason = sanitize (e.comment);
+        }
+      }
+    }
+
+    if (!r)
+      return true;
+
+    // Now check if the configuration is excluded/included via the patterns.
+    //
+    const string& cn (cfg.name);
+    string tg (cfg.target.string ());
+
+    for (const build_constraint& c: constrs)
     {
-      if (match (bc.config, bc.target, c))
-        return bc.exclusion;
+      if (path_match (c.config, cn) &&
+          (!c.target || path_match (*c.target, tg)))
+      {
+        if (!c.exclusion)
+          return false;
+
+        if (reason != nullptr)
+          *reason = sanitize (c.comment);
+
+        return true;
+      }
     }
 
     return false;