Skip go-oracle configuration if GOPATH not found

contrib/lang/go/extensions.el

@@ -23,23 +23,31 @@
 ;; https://github.com/jwiegley/use-package
 
 (defun go/init-go-oracle()
-  (load-file "$GOPATH/src/code.google.com/p/go.tools/cmd/oracle/oracle.el")
-  (add-hook 'go-mode-hook 'go-oracle-mode)
-  (spacemacs|diminish go-oracle-mode " O")
-  (evil-leader/set-key-for-mode 'go-mode
-    "moo" 'go-oracle-set-scope
-    "mo<" 'go-oracle-callers
-    "mo>" 'go-oracle-callees
-    "moc" 'go-oracle-peers
-    "mod" 'go-oracle-definition
-    "mof" 'go-oracle-freevars
-    "mog" 'go-oracle-callgraph
-    "moi" 'go-oracle-implements
-    "mop" 'go-oracle-pointsto
-    "mor" 'go-oracle-referrers
-    "mos" 'go-oracle-callstack
-    "mot" 'go-oracle-describe
-  ))
+  (let ((go-path (getenv "GOPATH")))
+    (if (not go-path)
+        (spacemacs/message (concat "Warning: GOPATH variable not found, "
+                                   "go-oracle configuration skipped."))
+      (load-file (concat (file-name-as-directory go-path)
+                         "src/code.google.com/p/go.tools/cmd/oracle/oracle.el"))
+      (add-hook 'go-mode-hook 'go-oracle-mode)
+      (spacemacs|diminish go-oracle-mode " O")
+      (evil-leader/set-key-for-mode 'go-mode
+        "moo" 'go-oracle-set-scope
+        "mo<" 'go-oracle-callers
+        "mo>" 'go-oracle-callees
+        "moc" 'go-oracle-peers
+        "mod" 'go-oracle-definition
+        "mof" 'go-oracle-freevars
+        "mog" 'go-oracle-callgraph
+        "moi" 'go-oracle-implements
+        "mop" 'go-oracle-pointsto
+        "mor" 'go-oracle-referrers
+        "mos" 'go-oracle-callstack
+        "mot" 'go-oracle-describe)
+
+      )
+    )
+  )
 
 (defun go/init-go-rename()
   (use-package go-rename