From 32edfff7aae15654d2cfa4a10da9b8f81e021bce Mon Sep 17 00:00:00 2001
From: Gordon Diggs <gordon@gordondiggs.com>
Date: Tue, 28 Feb 2017 11:48:42 -0500
Subject: [PATCH] Fix error when there are no config files

Fixes the following error:

      TypeError: Reduce of empty array with no initial value
          at Array.reduce (native)
          at Function.upgradeInstructions (/usr/src/app/lib/config_upgrader.js:272:20)
          at Object.<anonymous> (/usr/src/app/bin/eslint.js:239:37)
          at Module._compile (module.js:556:32)
          at Object.Module._extensions..js (module.js:565:10)
          at Module.load (module.js:473:32)
          at tryModuleLoad (module.js:432:12)
          at Function.Module._load (module.js:424:3)
          at Module.runMain (module.js:590:10)
          at run (bootstrap_node.js:394:7)

I couldn't find a good initial value to give to `reduce` to obtain the
correct functionality. There's no reason to reduce anyway if there are
no reports.
---
 lib/config_upgrader.js       |  6 +++++-
 test/config_upgrater_test.js | 13 +++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/config_upgrader.js b/lib/config_upgrader.js
index 9a4f39004..78cb8d9a6 100644
--- a/lib/config_upgrader.js
+++ b/lib/config_upgrader.js
@@ -269,7 +269,11 @@ class ConfigUpgrader {
       return report;
     });
 
-    return reports.reduce(function(a, b) { return a.concat([""]).concat(b); });
+    if (reports.length > 0) {
+      return reports.reduce(function(a, b) { return a.concat([""]).concat(b); });
+    } else {
+      return reports;
+    }
   }
 }
 
diff --git a/test/config_upgrater_test.js b/test/config_upgrater_test.js
index e6cba7123..1f1c356c0 100644
--- a/test/config_upgrater_test.js
+++ b/test/config_upgrater_test.js
@@ -55,6 +55,19 @@ describe("ConfigUpgrader", function() {
         });
       });
     });
+
+    it("doesn't care if there aren't any configs", function(done) {
+      temp.mkdir("code ", function(err, directory) {
+        if (err) { throw err; }
+
+        process.chdir(directory);
+
+        let report = ConfigUpgrader
+          .upgradeInstructions([directory + '/file.js'], directory);
+        expect(report).to.deep.eq([]);
+        done();
+      });
+    });
   });