From 6dcf87224a7e13550d664430bd149f42c8b12531 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 16 Aug 2021 09:38:16 +0200
Subject: Add pkg-build --noop-exit option

---
 bpkg/pkg-build.cli | 10 +++++++++-
 bpkg/pkg-build.cxx | 21 +++++++++++++++++++--
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/bpkg/pkg-build.cli b/bpkg/pkg-build.cli
index 02df2d1..2ae2948 100644
--- a/bpkg/pkg-build.cli
+++ b/bpkg/pkg-build.cli
@@ -345,12 +345,20 @@ namespace bpkg
 
     bool --no-refinement
     {
-      "Don't try to refine the configuration by offering drop any unused
+      "Don't try to refine the configuration by offering to drop any unused
        dependencies that were potentially left behind on the previous
        \cb{pkg-build} or \cb{pkg-drop} command execution if the command
        is otherwise a noop (performs no new package builds, upgrades, etc)."
     }
 
+    uint16_t --noop-exit
+    {
+      "<code>",
+
+      "Exit with the specified error code if the command execution is a noop
+       (performs no new package builds, upgrades, etc)."
+    }
+
     uint16_t --no-private-config
     {
       "<code>",
diff --git a/bpkg/pkg-build.cxx b/bpkg/pkg-build.cxx
index 1e8e9dd..f59c2c0 100644
--- a/bpkg/pkg-build.cxx
+++ b/bpkg/pkg-build.cxx
@@ -3203,6 +3203,17 @@ namespace bpkg
     //
     validate_options (o, ""); // Global package options.
 
+    if (o.noop_exit_specified ())
+    {
+      if (o.print_only ())
+        fail << "--noop-exit specified with --print-only";
+
+      // We can probably use build2's --structured-result to support this.
+      //
+      if (!o.configure_only ())
+        fail << "--noop-exit is only supported in --configure-only mode";
+    }
+
     if (o.update_dependent () && o.leave_dependent ())
       fail << "both --update-dependent|-U and --leave-dependent|-L "
            << "specified" <<
@@ -4693,6 +4704,9 @@ namespace bpkg
     {
       assert (rec_pkgs.empty ());
 
+      if (o.noop_exit_specified ())
+        return o.noop_exit ();
+
       info << "nothing to build";
       return 0;
     }
@@ -5935,10 +5949,13 @@ namespace bpkg
     // prerequsites got upgraded/downgraded and that the user may want to in
     // addition update (that update_dependents flag above).
     //
-    execute_plan (o, pkgs, false /* simulate */, find_prereq_database);
+    bool noop (!execute_plan (o,
+                              pkgs,
+                              false /* simulate */,
+                              find_prereq_database));
 
     if (o.configure_only ())
-      return 0;
+      return noop && o.noop_exit_specified () ? o.noop_exit () : 0;
 
     // update
     //
-- 
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