Unmangle private names ('__' prefix) in class declarations.

Fixes #166.

ASTree.cpp

@@ -1942,6 +1942,11 @@ PycRef<ASTNode> BuildFromCode(PycRef<PycCode> code, PycModule* mod)
                         break;
                     }
 
+                    // Return private names back to their original name
+                    const std::string class_prefix = std::string("_") + code->name()->strValue();
+                    if (varname->startsWith(class_prefix + std::string("__")))
+                        varname->setValue(varname->strValue().substr(class_prefix.size()));
+
                     PycRef<ASTNode> name = new ASTName(varname);
 
                     if (curblock->blktype() == ASTBlock::BLK_FOR

pyc_string.h

@@ -14,10 +14,18 @@ public:
     bool isEqual(PycRef<PycObject> obj) const override;
     bool isEqual(const std::string& str) const { return m_value == str; }
 
+    bool startsWith(const std::string& str) const
+    {
+        return m_value.substr(0, str.size()) == str;
+    }
+
     void load(class PycData* stream, class PycModule* mod) override;
 
     int length() const { return (int)m_value.size(); }
     const char* value() const { return m_value.c_str(); }
+    const std::string &strValue() const { return m_value; }
+
+    void setValue(std::string str) { m_value = std::move(str); }
 
 private:
     std::string m_value;

tests/input/private_name.py

@@ -0,0 +1,28 @@
+# Python mangles methods with a leading double-underscore with a leading
+# _<classname> prefix.  This should be removed when emitting the source
+#
+# Valid Pythons: all
+
+class Klass:
+    def __init__(self):
+        pass
+
+    def method(self):
+        pass
+
+    def _internal_name(self):
+        pass
+
+    def __private_name(self):
+        pass
+
+    var = 1
+    _internal_var = 2
+    __private_var = 3
+
+k = Klass()
+k.method()
+k._internal_name()
+
+# The following is not accessible due to mangling
+k.__private_name()

tests/tokenized/private_name.txt

@@ -0,0 +1,26 @@
+class Klass : <EOL>
+<INDENT>
+def __init__ ( self ) : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+def method ( self ) : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+def _internal_name ( self ) : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+def __private_name ( self ) : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+var = 1 <EOL>
+_internal_var = 2 <EOL>
+__private_var = 3 <EOL>
+<OUTDENT>
+k = Klass ( ) <EOL>
+k . method ( ) <EOL>
+k . _internal_name ( ) <EOL>
+k . __private_name ( ) <EOL>