raise SyntaxError when variable is used before global declaration

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/ErrorMessages.java

@@ -362,6 +362,7 @@ public abstract class ErrorMessages {
     public static final String MUST_BE_TUPLE_OF_CLASSES_NOT_P = "%s.%s must be tuple of classes, not '%p'";
     public static final String MUST_SPECIFY_FILTERS = "Must specify filters for FORMAT_RAW";
     public static final String MUTATED_DURING_UPDATE = "%s mutated during update";
+    public static final String NAME_IS_USED_BEFORE_GLOBAL = "name '%s' is used prior to global declaration";
     public static final String NAME_IS_ASSIGNED_BEFORE_GLOBAL = "name '%s' is assigned to before global declaration";
     public static final String NAME_IS_ASSIGNED_BEFORE_NONLOCAL = "name '%s' is assigned to before nonlocal declaration";
     public static final String NAME_NOT_DEFINED = "name '%s' is not defined";

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/PythonSSTNodeFactory.java

@@ -160,6 +160,9 @@ public SSTNode registerGlobal(String[] names, int startOffset, int endOffset) {
                 // The slot is created by assignment or declaration
                 throw errors.raiseInvalidSyntax(source, createSourceSection(startOffset, endOffset), ErrorMessages.NAME_IS_ASSIGNED_BEFORE_GLOBAL, name);
             }
+            if (scopeInfo.getSeenVars() != null && scopeInfo.getSeenVars().contains(name)) {
+                throw errors.raiseInvalidSyntax(source, createSourceSection(startOffset, endOffset), ErrorMessages.NAME_IS_USED_BEFORE_GLOBAL, name);
+            }
             scopeInfo.addExplicitGlobalVariable(name);
             // place the global variable into global space, see test_global_statemnt.py
             globalScope.addExplicitGlobalVariable(name);

graalpython/lib-graalpython/unicodedata.py

@@ -44,9 +44,9 @@
 
 @__graalpython__.builtin
 def __get_c_unicodedata():
+    global c_unicodedata_module
     if c_unicodedata_module is None:
         import _cpython_unicodedata
-        global c_unicodedata_module
         c_unicodedata_module = _cpython_unicodedata
     return c_unicodedata_module