libutil: allow marking settings as deprecated

this is a bit of a hack, but it's apparently the cleanest way of doing
this in the absence of any kind of priority/provenance information for
values of some given setting. we'll need this to deprecate build-hook.

Change-Id: I03644a9c3f17681c052ecdc610b4f1301266ab9e

1 files changed, 7 insertions, 3 deletions

diff --git a/src/libutil/config-impl.hh b/src/libutil/config-impl.hh
index 756175f95..8e3a1e408 100644
--- a/src/libutil/config-impl.hh
+++ b/src/libutil/config-impl.hh
@@ -66,9 +66,13 @@ void BaseSetting<T>::appendOrSet(T newValue, bool append)
 template<typename T>
 void BaseSetting<T>::set(const std::string & str, bool append)
 {
-    if (experimentalFeatureSettings.isEnabled(experimentalFeature))
-        appendOrSet(parse(str), append);
-    else {
+    if (experimentalFeatureSettings.isEnabled(experimentalFeature)) {
+        auto parsed = parse(str);
+        if (deprecated && (append || parsed != value)) {
+            warn("deprecated setting '%s' found (set to '%s')", name, str);
+        }
+        appendOrSet(std::move(parsed), append);
+    } else {
         assert(experimentalFeature);
         warn("Ignoring setting '%s' because experimental feature '%s' is not enabled",
             name,