allow conditions to directly imply interpolation variations

lib/trace.js

@@ -330,6 +330,24 @@ Trace.prototype.getLoadRecord = function(canonical, traceOpts, parentStack) {
       if (condition.indexOf('|') == -1)
         condition += '|default';
 
+      // if the condition values have been provided via traceOpts.conditions
+      // then we dont need to work out variations from the file system and can just take what is given
+      if (traceOpts.conditions[condition]) {
+        var branches = {};
+        traceOpts.conditions[condition].forEach(function(c) {
+          var branchCanonical = canonical.substr(0, interpolationMatch.index) + c + canonical.substr(interpolationMatch[0].length + interpolationMatch.index);
+          branches[c] = branchCanonical;
+        });
+        return {
+          name: canonical,
+          fresh: false,
+          conditional: {
+            condition: condition,
+            branches: branches
+          }
+        };
+      }
+
       var metadata = {};
       return Promise.resolve(loader.locate({ name: normalized.replace(interpolationRegEx, '*'), metadata: metadata }))
       .then(function(address) {