interpolation: fix: source_id mapping

middleware/interpolate.js

@@ -105,8 +105,9 @@ function interpolate( parsed_text, hit, cb ){
 
       // -- source_id --
       // note: interpolated values have no source_id
-      if( hit.hasOwnProperty( 'source_id' ) ){
+      delete hit.source_id; // remove original street source_id
-        hit.source_id = hit.source_id;
+      if( data.properties.hasOwnProperty( 'source_id' ) ){
+        hit.source_id = data.properties.source_id;
       }
 
       // -- address_parts --

test/unit/middleware/interpolate.js

@@ -149,7 +149,8 @@ module.exports.tests.hit = function(test, common) {
         layer: 'street',
         center_point: { lat: 1, lon: 1 },
         address_parts: { street: 'sesame rd' },
-        name: { default: 'street name' }
+        name: { default: 'street name' },
+        source_id: '123456'
       }
     ]};
 
@@ -180,7 +181,8 @@ module.exports.tests.hit = function(test, common) {
           center_point: { lat: 22.2, lon: -33.3 },
           address_parts: { street: 'sesame rd', number: '100A' },
           name: { default: '100A street name' },
-          source: 'openstreetmap'
+          source: 'openstreetmap',
+          source_id: 'way:111111'
         }
       ]});
       t.end();