From 43dccfeb195d9f739ac78f6d1cd79fd16fc2cef4 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 15 May 2019 08:22:16 +0200
Subject: Redo ad hoc group member matching

---
 build2/algorithm.cxx | 92 ++++++++++++++++++++++------------------------------
 1 file changed, 38 insertions(+), 54 deletions(-)

diff --git a/build2/algorithm.cxx b/build2/algorithm.cxx
index 2e3fe83..10f1cdf 100644
--- a/build2/algorithm.cxx
+++ b/build2/algorithm.cxx
@@ -416,6 +416,44 @@ namespace build2
     target& t (*l.target);
     target::opstate& s (t[a]);
 
+    // Intercept and handle matching an ad hoc group member.
+    //
+    if (t.adhoc_member ())
+    {
+      assert (!step);
+
+      const target& g (*t.group);
+
+      // It feels natural to "convert" this call to the one for the group,
+      // including the try_match part. Semantically, we want to achieve the
+      // following:
+      //
+      // [try_]match (a, g);
+      // match_recipe (l, group_recipe);
+      //
+      auto df = make_diag_frame (
+        [a, &t](const diag_record& dr)
+        {
+          if (verb != 0)
+            dr << info << "while matching group rule to " << diag_do (a, t);
+        });
+
+      pair<bool, target_state> r (match (a, g, 0, nullptr, try_match));
+
+      if (r.first)
+      {
+        if (r.second != target_state::failed)
+        {
+          match_inc_dependens (a, g);
+          match_recipe (l, group_recipe);
+        }
+      }
+      else
+        l.offset = target::offset_tried;
+
+      return r; // Group state.
+    }
+
     try
     {
       // Continue from where the target has been left off.
@@ -530,55 +568,6 @@ namespace build2
       if (try_match && l.offset == target::offset_tried)
         return make_pair (false, target_state::unknown);
 
-      // Handle matching ad hoc group member.
-      //
-      if (ct.adhoc_member ())
-      {
-        const target& g (*ct.group);
-
-        // It feels natural to "convert" this call to the one for the group,
-        // including the try_match and async parts. However, that async part
-        // is tricky: we will be called again to finish the match (the else-
-        // block below) where we need to perform the equivalent conversion.
-        // Semantically, we want to achieve the following:
-        //
-        // match (a, g);                    |  match_async (a, g);
-        //                                  |  match (a, g);
-        // match_recipe (l, group_recipe);  |  match_recipe (l, group_recipe);
-        //
-        // We also have to "unstack" this lock to avoid racing with stack
-        // modifications by the asynchronous match (see below). Since an ad
-        // hoc member doesn't have any prerequisites of its own (and thus
-        // cannot depend on the group), skipping this link during the cycle
-        // detection feels harmless (note that the other way around is
-        // possible and still works).
-        //
-        l.unstack ();
-
-
-#if 0   // The same story as with the lock stack. I think the only way to
-        // make this work is to somehow pass the member down to match_impl().
-        auto df = make_diag_frame (
-          [a, &ct](const diag_record& dr)
-          {
-            if (verb != 0)
-              dr << info << "while matching rule group to " << diag_do (a, ct);
-          });
-#endif
-
-        auto r (match (a, g, start_count, task_count, try_match));
-
-        if (r.first)
-        {
-          match_inc_dependens (a, g);
-          match_recipe (l, group_recipe);
-        }
-        else
-          l.offset = target::offset_tried;
-
-        return r; // Group state.
-      }
-
       if (task_count == nullptr)
         return match_impl (l, false /* step */, try_match);
 
@@ -627,11 +616,6 @@ namespace build2
       if (l.offset >= target::offset_busy)
         return make_pair (true, target_state::busy);
 
-      // Handle matching ad hoc group member (the finish part; see above).
-      //
-      if (ct.adhoc_member ())
-        return match (a, *ct.group, 0, nullptr);
-
       // Fall through.
     }
 
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