glasser's responses on the -rc changes

packages/constraint-solver/constraint-solver.js

@@ -265,8 +265,12 @@ ConstraintSolver.PackagesResolver.prototype.resolve = function (
         throw e;
     }
   }
+  var ret = {
+    answer:  resolverResultToPackageMap(res),
+    usedRCs: resolverOptions["useRCs"]
+  };
 
-  return resolverResultToPackageMap(res);
+  return ret;
 };
 
 var removeUnibuild = function (unitName) {

packages/constraint-solver/resolver.js

@@ -390,7 +390,8 @@ ConstraintSolver.Constraint.prototype.isSatisfied = function (
   }
 
   if (self.type === "any-reasonable") {
-    // Non-prerelease versions are always reasonable.
+    // Non-prerelease versions are always reasonable, and if we are OK with
+    // using RCs all the time, then they are reasonable too.
     if (!/-/.test(candidateUV.version) ||
         resolveContext.useRCsOK)
       return true;
@@ -421,9 +422,10 @@ ConstraintSolver.Constraint.prototype.isSatisfied = function (
     return self.version === candidateUV.version;
   }
 
-  // If you're not asking for a pre-release, you'll only get it if it was a top
-  // level explicit mention (eg, in the release).
-  if (/-/.test(candidateUV.version)) {
+  // If you're not asking for a pre-release (and you are not in pre-releases-OK
+  // mode), you'll only get it if it was a top level explicit mention (eg, in
+  // the release).
+  if (/-/.test(candidateUV.version) && !resolveContext.useRCsOK) {
     if (self.version === candidateUV.version)
       return true;
     if (!_.has(resolveContext.topLevelPrereleases, self.name) ||

tools/catalog.js

@@ -528,13 +528,15 @@ _.extend(CompleteCatalog.prototype, {
       messageAfterMs: 1000,
       message: "Figuring out the best package versions to use. This may take a moment."
     });
+
+    var ret;
     try {
       // Then, call the constraint solver, to get the valid transitive subset of
       // those versions to record for our solution. (We don't just return the
       // original version lock because we want to record the correct transitive
       // dependencies)
       try {
-        return self.resolver.resolve(deps, constr, resolverOpts);
+        ret = self.resolver.resolve(deps, constr, resolverOpts);
       } catch (e) {
         // Maybe we only failed because we need to refresh. Try to refresh
         // (unless we already are) and retry.
@@ -544,12 +546,27 @@ _.extend(CompleteCatalog.prototype, {
         }
         catalog.official.refresh();
         self.resolver || self._initializeResolver();
-        return self.resolver.resolve(deps, constr, resolverOpts);
+        ret = self.resolver.resolve(deps, constr, resolverOpts);
       }
     } finally {
       patience.stop();
     }
+    if (ret["usedRCs"]) {
+      process.stderr.write(
+"\nWARNING: In order to resolve constraints, we had to use the following "+
+ "experimental package versions:\n");
+      var packages = "";
+      _.each(ret.answer, function(version, package) {
+        if (version.split('-').length > 1) {
+          packages+= package + "@" + version + ", ";
+        }
+      });
+      packages = packages.slice(0, packages.length - 2);
+      process.stderr.write(packages + "\n\n");
+    }
+    return ret.answer;
   },
+
   // Refresh the packages in the catalog.
   //
   // Reread server data from data.json on disk, then load local overrides on top