Initialize $0 to a String as RubyGems expects it to

(cherry picked from commit 754db2b)

Author: eregon

CHANGELOG.md

@@ -8,6 +8,16 @@ Bug fixes:
 * Temporary variables are no longer visible in the debugger.
 * Setting breakpoints on some lines has been fixed.
 * The OpenSSL C extension is now always recompiled, fixing various bugs when using the extension (e.g., when using Bundler in TravisCI) (#1676, #1627, #1632).
+* Initialize `$0` when not run from the 'ruby' launcher, which is needed to `require` gems (#1653).
+
+Compatibility:
+
+* `do...end` blocks can now have `rescue/else/ensure` clauses like MRI (#1618).
+
+# 1.0 RC 16, 19 April 2019
+Changes:
+
+* `TruffleRuby.sulong?` has been replaced by `TruffleRuby.cexts?`, and `TruffleRuby.graal?` has been replaced by `TruffleRuby.jit?`. The old methods will continue to work for now, but will produce warnings, and will be removed at a future release.
 
 # 1.0 RC 16
 

src/main/java/org/truffleruby/core/CoreLibrary.java

@@ -849,6 +849,10 @@ private void afterLoadCoreLibrary() {
         assert Layouts.CLASS.isClass(eagainWaitWritable);
 
         findGlobalVariableStorage();
+
+        // Initialize $0 so it is set to a String as RubyGems expect, also when not run from the RubyLauncher
+        DynamicObject dollarZeroValue = StringOperations.createString(context, StringOperations.encodeRope("-", USASCIIEncoding.INSTANCE, CodeRange.CR_7BIT));
+        getContext().getCoreLibrary().getGlobalVariables().getStorage("$0").setValueInternal(dollarZeroValue);
     }
 
     @TruffleBoundary