Do not omit backtrace when $ERROR_INFO is the rescue body

Author: bjfish

CHANGELOG.md

@@ -53,6 +53,7 @@ Bug fixes:
 * Fixed `Kernel#clone` for `nil`, `true`, `false`, `Integer`, and `Symbol`.
 * Make top-level methods available in `Context#getBindings()` (#1838).
 * Made `Kernel#caller_locations` accept a range argument, and return `nil` when appropriate.
+* Fixed issue with missing backtrace for `rescue $ERROR_INFO` (#1660).
 
 Compatibility:
 

spec/ruby/library/English/alias_spec.rb

@@ -0,0 +1,8 @@
+require_relative '../../spec_helper'
+
+describe "alias keyword" do
+  it "aliases $ERROR_INFO to $! in English and $ERROR_INFO still returns a backtrace" do
+    alias $ERROR_INFO $!
+    (1 / 0 rescue $ERROR_INFO).should_not == nil
+  end
+end

src/main/java/org/truffleruby/parser/BodyTranslator.java

@@ -2842,7 +2842,8 @@ public RubyNode visitRescueNode(RescueParseNode node) {
         if (context.getOptions().BACKTRACES_OMIT_UNUSED && rescueBody != null &&
                 rescueBody.getBodyNode() instanceof SideEffectFree /* allow `expression rescue $!` pattern */ &&
                 (!(rescueBody.getBodyNode() instanceof GlobalVarParseNode) ||
-                        !((GlobalVarParseNode) rescueBody.getBodyNode()).getName().equals("$!")) &&
+                        (!((GlobalVarParseNode) rescueBody.getBodyNode()).getName().equals("$!") &&
+                                !((GlobalVarParseNode) rescueBody.getBodyNode()).getName().equals("$ERROR_INFO"))) &&
                 rescueBody.getOptRescueNode() == null) {
             canOmitBacktrace = true;
         }