Improve ExtractFunction pass error printing (#4747)

* Improve ExtractFunction pass error printing.

* Update lint

1 files changed, 3 insertions, 2 deletions

diff --git a/src/passes/ExtractFunction.cpp b/src/passes/ExtractFunction.cpp
index 0939ebe28..f75c04cbe 100644
--- a/src/passes/ExtractFunction.cpp
+++ b/src/passes/ExtractFunction.cpp
@@ -80,10 +80,11 @@ struct ExtractFunctionIndex : public Pass {
     }
     Index i = std::stoi(index);
     if (i >= module->functions.size()) {
-      Fatal() << "Invalid function index";
+      Fatal() << "Out of bounds function index " << i << "! (module has only "
+              << module->functions.size() << " functions)";
     }
     // Assumes imports are at the beginning
-    Name name = module->functions[std::stoi(index)]->name;
+    Name name = module->functions[i]->name;
     extract(runner, module, name);
   }
 };