Preprocessor: handle '#undef' better. Ticket: #2131

lib/preprocessor.cpp

@@ -1798,6 +1798,10 @@ std::string Preprocessor::handleIncludes(const std::string &code, const std::str
                 }
             }
 
+            else if (line.compare(0,7,"#undef ") == 0) {
+                defs.erase(line.substr(7));
+            }
+
             else {
                 ostr << line;
             }

test/testpreprocessor.cpp

@@ -2912,6 +2912,22 @@ private:
                 ASSERT_EQUALS("\n\n\n\n\n\n\n4\n\n", actual);
             }
         }
+
+        // #undef
+        {
+            const std::string code("#ifndef X\n"
+                                   "#define X\n"
+                                   "123\n"
+                                   "#endif\n");
+
+            defs.clear();
+            const std::string actual1(preprocessor.handleIncludes(code,filePath,includePaths,defs));
+
+            defs.clear();
+            const std::string actual(preprocessor.handleIncludes(code + "#undef X\n" + code, filePath, includePaths, defs));
+
+            ASSERT_EQUALS(actual1 + "\n" + actual1, actual);
+        }
     }
 };