Improve skipped update diagnostics

Instead of printing a line for each target skipped we now print a summary
with count at the end. We also now show the skip count in progress.

4 files changed, 36 insertions, 11 deletions

diff --git a/build2/cc/compile.cxx b/build2/cc/compile.cxx
index 6022fb6..33a0d6d 100644
--- a/build2/cc/compile.cxx
+++ b/build2/cc/compile.cxx
@@ -3985,13 +3985,8 @@ namespace build2
       {
         if (md.touch)
         {
-          // Getting "everything up to date" after modifying a file can be
-          // unnerving. So calm the user down.
-          //
-          if (verb == 1)
-            text << "skip " << s;
-
           touch (tp, false, 2);
+          skip_count.fetch_add (1, memory_order_relaxed);
         }
 
         t.mtime (md.mt);
diff --git a/build2/context.cxx b/build2/context.cxx
index d074d9c..68c7e6d 100644
--- a/build2/context.cxx
+++ b/build2/context.cxx
@@ -204,6 +204,7 @@ namespace build2
 
   atomic_count dependency_count;
   atomic_count target_count;
+  atomic_count skip_count;
 
   bool keep_going = false;
 
diff --git a/build2/context.hxx b/build2/context.hxx
index dbb41ae..c3e0595 100644
--- a/build2/context.hxx
+++ b/build2/context.hxx
@@ -283,11 +283,13 @@ namespace build2
   // with the expectation of it reaching 0. Used as a sanity check.
   //
   // The target count is incremented after a non-noop recipe is matched and
-  // decremented after such recipe has been executed. Used for progress
-  // monitoring.
+  // decremented after such recipe has been executed. If such a recipe has
+  // skipped updating the target, then it should increment the skip count.
+  // These two counters are used for progress monitoring and diagnostics.
   //
   extern atomic_count dependency_count;
   extern atomic_count target_count;
+  extern atomic_count skip_count;
 
   inline void
   set_current_mif (const meta_operation_info& mif)
@@ -307,9 +309,11 @@ namespace build2
     current_on++;
     current_mode = inner_oif.mode;
 
-    // Serial.
+    // Reset counters (serial execution).
+    //
     dependency_count.store (0, memory_order_relaxed);
     target_count.store (0, memory_order_relaxed);
+    skip_count.store (0, memory_order_relaxed);
   }
 
   // Keep going flag.
diff --git a/build2/operation.cxx b/build2/operation.cxx
index 09e7b8c..ea1e06e 100644
--- a/build2/operation.cxx
+++ b/build2/operation.cxx
@@ -268,10 +268,20 @@ namespace build2
           [init, incr, what] (size_t c) -> size_t
           {
             size_t p ((init - c) * 100 / init);
+            size_t s (skip_count.load (memory_order_relaxed));
+
             diag_progress_lock pl;
             diag_progress  = ' ';
             diag_progress += to_string (p);
             diag_progress += what;
+
+            if (s != 0)
+            {
+              diag_progress += " (";
+              diag_progress += to_string (s);
+              diag_progress += " skipped)";
+            }
+
             return c - incr;
           });
       }
@@ -302,6 +312,11 @@ namespace build2
       wg.wait ();
     }
 
+    // We are now running serially.
+    //
+
+    sched.tune (0); // Restore original scheduler settings.
+
     // Clear the progress if present.
     //
     if (mg)
@@ -310,9 +325,19 @@ namespace build2
       diag_progress.clear ();
     }
 
-    sched.tune (0); // Restore original scheduler settings.
+    // Print skip count if not zero. Note that we print it regardless of the
+    // quiet flag since this is essentially a "summary" of all the commands
+    // that we did not (and, in fact, used to originally) print.
+    //
+    if (verb != 0)
+    {
+      if (size_t s = skip_count.load (memory_order_relaxed))
+      {
+        text << "skipped " << diag_doing (a) << ' ' << s << " target(s)";
+      }
+    }
 
-    // We are now running serially. Re-examine them all.
+    // Re-examine all the targets and print diagnostics.
     //
     bool fail (false);
     for (const void* vt: ts)