From 743273bd381a132c272226af00381da0494e8920 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 15 Feb 2022 15:59:22 +0200
Subject: Diagnose various misuses of library metadata protocol

---
 libbuild2/cc/common.cxx    |  4 ++++
 libbuild2/cc/functions.cxx |  9 +++++++++
 libbuild2/target.hxx       |  2 +-
 libbuild2/target.ixx       | 21 ++++++++++++++-------
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/libbuild2/cc/common.cxx b/libbuild2/cc/common.cxx
index 09a1752..ccb678c 100644
--- a/libbuild2/cc/common.cxx
+++ b/libbuild2/cc/common.cxx
@@ -320,6 +320,10 @@ namespace build2
             if (pt.adhoc || pt == nullptr)
               continue;
 
+            if (marked (pt))
+              fail << "implicit dependency cycle detected involving library "
+                   << l;
+
             bool la;
             const file* f;
 
diff --git a/libbuild2/cc/functions.cxx b/libbuild2/cc/functions.cxx
index e05c707..8a48e66 100644
--- a/libbuild2/cc/functions.cxx
+++ b/libbuild2/cc/functions.cxx
@@ -74,6 +74,11 @@ namespace build2
       {
         name& n (*i), o;
         const target& t (to_target (*bs, move (n), move (n.pair ? *++i : o)));
+
+        if (!t.matched (a))
+          fail << t << " is not matched" <<
+            info << "make sure this target is listed as prerequisite";
+
         d.f (r, vs, *m, *bs, a, t);
       }
 
@@ -174,6 +179,10 @@ namespace build2
             (la = (f = t.is_a<liba>  ())) ||
             (     (f = t.is_a<libs>  ())))
         {
+          if (!t.matched (a))
+            fail << t << " is not matched" <<
+              info << "make sure this target is listed as prerequisite";
+
           d.f (ls, r, vs, *m, *bs, a, *f, la, li);
         }
         else
diff --git a/libbuild2/target.hxx b/libbuild2/target.hxx
index 809bf8b..5eed0a5 100644
--- a/libbuild2/target.hxx
+++ b/libbuild2/target.hxx
@@ -636,7 +636,7 @@ namespace build2
     const opstate& operator[] (action a) const {return state[a];}
 
     // Return true if the target has been matched for the specified action.
-    // This function can only be called during execution.
+    // This function can only be called during the match or execute phases.
     //
     bool
     matched (action) const;
diff --git a/libbuild2/target.ixx b/libbuild2/target.ixx
index b1e21ae..05f9698 100644
--- a/libbuild2/target.ixx
+++ b/libbuild2/target.ixx
@@ -158,17 +158,24 @@ namespace build2
   inline bool target::
   matched (action a) const
   {
-    assert (ctx.phase == run_phase::execute);
+    assert (ctx.phase == run_phase::match ||
+            ctx.phase == run_phase::execute);
 
     const opstate& s (state[a]);
-
-    // Note that while the target could be being executed, we should see at
-    // least offset_matched since it must have been "achieved" before the
-    // phase switch.
-    //
     size_t c (s.task_count.load (memory_order_relaxed) - ctx.count_base ());
 
-    return c >= offset_matched;
+    if (ctx.phase == run_phase::match)
+    {
+      return c == offset_applied;
+    }
+    else
+    {
+      // Note that while the target could be being executed, we should see at
+      // least offset_matched since it must have been "achieved" before the
+      // phase switch.
+      //
+      return c >= offset_matched;
+    }
   }
 
   LIBBUILD2_SYMEXPORT target_state
-- 
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