From b4ae4f68d1d9456dc9bb6b9e1a31f8390605f882 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 21 Nov 2017 15:34:01 +0200
Subject: Recursively check timestamps of libraries we are linking

---
 build2/cc/link.cxx | 33 +++++++++++++++++++++++++++------
 build2/cc/link.hxx |  1 +
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/build2/cc/link.cxx b/build2/cc/link.cxx
index 7f1e8d8..4f1eea5 100644
--- a/build2/cc/link.cxx
+++ b/build2/cc/link.cxx
@@ -1000,12 +1000,20 @@ namespace build2
 
     void link::
     hash_libraries (sha256& cs,
+                    bool& update, timestamp mt,
                     const file& l, bool la, lflags lf,
                     const scope& bs, action act, linfo li) const
     {
       auto imp = [] (const file&, bool la) {return la;};
 
-      auto lib = [&cs, this] (const file* l, const string& p, lflags f, bool)
+      struct data
+      {
+        sha256&   cs;
+        bool&     update;
+        timestamp mt;
+      } d {cs, update, mt};
+
+      auto lib = [&d, this] (const file* l, const string& p, lflags f, bool)
       {
         if (l != nullptr)
         {
@@ -1016,11 +1024,15 @@ namespace build2
           if (l->member != nullptr && l->is_a<libs> () && tclass == "windows")
             l = &l->member->as<file> ();
 
-          cs.append (f);
-          cs.append (l->path ().string ());
+          d.cs.append (f);
+          d.cs.append (l->path ().string ());
+
+          // Check if this library renders us out of date.
+          //
+          d.update = d.update || l->newer (d.mt);
         }
         else
-          cs.append (p);
+          d.cs.append (p);
       };
 
       auto opt = [&cs, this] (
@@ -1522,15 +1534,24 @@ namespace build2
             // Link all the dependent interface libraries (shared) or interface
             // and implementation (static), recursively.
             //
+            // Also check if any of them render us out of date. The tricky
+            // case is, say, a utility library (static) that depends on a
+            // shared library. When the shared library is updated, there is no
+            // reason to re-archive the utility but those who link the utility
+            // have to "see through" the changes in the shared library.
+            //
             if (a || s)
-              hash_libraries (cs, *f, a, p.data, bs, act, li);
+            {
+              hash_libraries (cs, update, mt, *f, a, p.data, bs, act, li);
+              f = nullptr; // Timestamp checked by hash_libraries().
+            }
             else
               cs.append (f->path ().string ());
           }
           else
             f = pt->is_a<exe> (); // Consider executable mtime (e.g., linker).
 
-          // Check if this input renders us out-of-date.
+          // Check if this input renders us out of date.
           //
           if (f != nullptr)
             update = update || f->newer (mt);
diff --git a/build2/cc/link.hxx b/build2/cc/link.hxx
index dc5f70a..c26102d 100644
--- a/build2/cc/link.hxx
+++ b/build2/cc/link.hxx
@@ -81,6 +81,7 @@ namespace build2
 
       void
       hash_libraries (sha256&,
+                      bool&, timestamp,
                       const file&, bool, lflags,
                       const scope&, action, linfo) const;
 
-- 
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