Add --silent, remap verbosity 0 to 1 while building modules unless silent

Failed that, we may have long periods of seemingly nothing happening (e.g.,
during implicit bdep sync) while we quietly update the module, which may look
like things have hung up.

4 files changed, 31 insertions, 4 deletions

diff --git a/libbuild2/diagnostics.cxx b/libbuild2/diagnostics.cxx
index 71f3d48..f1b8f74 100644
--- a/libbuild2/diagnostics.cxx
+++ b/libbuild2/diagnostics.cxx
@@ -21,6 +21,7 @@ namespace build2
   // set from options.
   //
   uint16_t verb = 0;
+  bool silent = true;
 
   optional<bool> diag_progress_option;
 
@@ -30,9 +31,12 @@ namespace build2
   bool stderr_term = false;
 
   void
-  init_diag (uint16_t v, optional<bool> p, bool nl, bool nc, bool st)
+  init_diag (uint16_t v, bool s, optional<bool> p, bool nl, bool nc, bool st)
   {
+    assert (!s || v == 0);
+
     verb = v;
+    silent = s;
     diag_progress_option = p;
     diag_no_line = nl;
     diag_no_column = nc;
diff --git a/libbuild2/diagnostics.hxx b/libbuild2/diagnostics.hxx
index 5d69132..26f602a 100644
--- a/libbuild2/diagnostics.hxx
+++ b/libbuild2/diagnostics.hxx
@@ -49,7 +49,7 @@ namespace build2
     print_process (args.data (), n != 0 ? n : args.size ());
   }
 
-  // Program verbosity level (-v/--verbose).
+  // Program verbosity level (-v/--verbose plus --silent).
   //
   // 0 - disabled
   // 1 - high-level information messages
@@ -59,13 +59,17 @@ namespace build2
   // 5 - information helpful to the developer
   // 6 - even more detailed information
   //
+  // If silent is true, then the level must be 0 (silent is level 0 that
+  // cannot be relaxed in certain contexts).
+  //
   // While uint8 is more than enough, use uint16 for the ease of printing.
   //
 
   // Forward-declarated in <libbuild2/utility.hxx>.
   //
+  // const uint16_t verb_never = 7;
   // extern uint16_t verb;
-  // const  uint16_t verb_never = 7;
+  // extern bool silent;
 
   template <typename F> inline void l1 (const F& f) {if (verb >= 1) f ();}
   template <typename F> inline void l2 (const F& f) {if (verb >= 2) f ();}
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index b73ddb3..50c6d53 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -262,6 +262,21 @@ namespace build2
                            ? scheduler::tune_guard (ctx.sched, 0)
                            : scheduler::tune_guard ());
 
+          // Remap verbosity level 0 to 1 unless we were requested to be
+          // silent. Failed that, we may have long periods of seemingly
+          // nothing happening while we quietly update the module, which
+          // may look like things have hung up.
+          //
+          // @@ CTX: modifying global verbosity level won't work if we have
+          //         multiple top-level contexts running in parallel.
+          //
+          auto verbg = make_guard (
+            [z = !silent && verb == 0 ? (verb = 1, true) : false] ()
+            {
+              if (z)
+                verb = 0;
+            });
+
           // Note that for now we suppress progress since it would clash with
           // the progress of what we are already doing (maybe in the future we
           // can do save/restore but then we would need some sort of
diff --git a/libbuild2/utility.hxx b/libbuild2/utility.hxx
index 536898e..1d5c7bb 100644
--- a/libbuild2/utility.hxx
+++ b/libbuild2/utility.hxx
@@ -97,15 +97,19 @@ namespace build2
   // Initialize the diagnostics state. Should be called once early in main().
   // Default values are for unit tests.
   //
+  // If silent is true, verbosity should be 0.
+  //
   LIBBUILD2_SYMEXPORT void
   init_diag (uint16_t verbosity,
+             bool silent = false,
              optional<bool> progress = nullopt,
              bool no_lines = false,
              bool no_columns = false,
              bool stderr_term = false);
 
-  LIBBUILD2_SYMEXPORT extern uint16_t verb;
   const uint16_t verb_never = 7;
+  LIBBUILD2_SYMEXPORT extern uint16_t verb;
+  LIBBUILD2_SYMEXPORT extern bool silent;
 
   // --[no-]progress
   //