fix: report missing import properly in loadSync

src/root.js

@@ -98,10 +98,10 @@ Root.prototype.load = function load(filename, options, callback) {
         /* istanbul ignore if */
         if (!callback)
             return;
-        var cb = callback;
-        callback = null;
         if (sync)
             throw err;
+        var cb = callback;
+        callback = null;
         cb(err, root);
     }
 

tests/api_root.js

@@ -67,6 +67,29 @@ tape.test("reflected roots", function(test) {
         });
     });
 
+    test.test(test.name + " - missing import", function(test) {
+        var root = new Root();
+        test.plan(2);
+        root.load("tests/data/badimport.proto", function(err) {
+            test.ok(err, "should return an error when an imported file does not exist");
+            test.match(err.toString(), /nonexistent\.proto/, "should mention the file name which was not found");
+            test.end();
+        });
+    });
+
+    test.test(test.name + " - missing import, sync load", function(test) {
+        var root = new Root();
+        test.plan(2);
+        try {
+            root.loadSync("tests/data/badimport.proto");
+            root.resolveAll();
+        } catch (err) {
+            test.ok(err, "should return an error when an imported file does not exist");
+            test.match(err.toString(), /nonexistent\.proto/, "should mention the file name which was not found");
+        }
+        test.end();
+    });
+
     test.test(test.name + " - skipped", function(test) {
         var root = new Root();
         root.resolvePath = function() {

tests/data/badimport.proto

@@ -0,0 +1,7 @@
+syntax = "proto3";
+
+import "nonexistent.proto";
+
+message Message {
+  NonExistent field = 1;
+}