Reimplement .compare() in terms of a visitor

Reworked the :meth:`.ClauseElement.compare` methods in terms of a new
visitor-based approach, and additionally added test coverage ensuring that
all :class:`.ClauseElement` subclasses can be accurately compared
against each other in terms of structure.   Structural comparison
capability is used to a small degree within the ORM currently, however
it also may form the basis for new caching features.

Fixes: #4336
Change-Id: I581b667d8e1642a6c27165cc9f4aded1c66effc6

1 files changed, 12 insertions, 0 deletions

diff --git a/test/ext/test_compiler.py b/test/ext/test_compiler.py
index ac6af0a96..ccd79f8d1 100644
--- a/test/ext/test_compiler.py
+++ b/test/ext/test_compiler.py
@@ -274,6 +274,18 @@ class UserDefinedTest(fixtures.TestBase, AssertsCompiledSQL):
             dialect=postgresql.dialect(),
         )
 
+    def test_functions_args_noname(self):
+        class myfunc(FunctionElement):
+            pass
+
+        @compiles(myfunc)
+        def visit_myfunc(element, compiler, **kw):
+            return "myfunc%s" % (compiler.process(element.clause_expr, **kw),)
+
+        self.assert_compile(myfunc(), "myfunc()")
+
+        self.assert_compile(myfunc(column("x"), column("y")), "myfunc(x, y)")
+
     def test_function_calls_base(self):
         from sqlalchemy.dialects import mssql