From 04fa56d0c07b66c77d0fdd6cb4419efb890043eb Mon Sep 17 00:00:00 2001
From: Schuyler Cebulskie <Gawdl3y@gawdl3y.com>
Date: Sun, 24 Mar 2019 16:45:34 -0400
Subject: [PATCH] Improve structure extension errors

---
 src/util/Structures.js | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/util/Structures.js b/src/util/Structures.js
index 4ac562606..62646b404 100644
--- a/src/util/Structures.js
+++ b/src/util/Structures.js
@@ -45,17 +45,22 @@ class Structures {
     if (typeof extender !== 'function') {
       const received = `(received ${typeof extender})`;
       throw new TypeError(
-        `"extender" argument must be a function that returns the extended structure class/prototype ${received}`
+        `"extender" argument must be a function that returns the extended structure class/prototype ${received}.`
       );
     }
 
     const extended = extender(structures[structure]);
     if (typeof extended !== 'function') {
-      throw new TypeError('The extender function must return the extended structure class/prototype.');
+      const received = `(received ${typeof extended})`;
+      throw new TypeError(`The extender function must return the extended structure class/prototype ${received}.`);
     }
-    if (Object.getPrototypeOf(extended) !== structures[structure]) {
+
+    const prototype = Object.getPrototypeOf(extended);
+    if (prototype !== structures[structure]) {
+      const received = `${extended.name || 'unnamed'}${prototype.name ? ` extends ${prototype.name}` : ''}`;
       throw new Error(
-        'The class/prototype returned from the extender function must extend the existing structure class/prototype.'
+        'The class/prototype returned from the extender function must extend the existing structure class/prototype' +
+        ` (received function ${received}; expected extension of ${structures[structure].name}).`
       );
     }