Genericize str() for types

Remove lookup logic that attempts to locate a dialect for a type,
just use StrSQLTypeCompiler.

Cleaned up the internal ``str()`` for datatypes so that all types produce a
string representation without any dialect present, including that it works
for third-party dialect types without that dialect being present.  The
string representation defaults to being the UPPERCASE name of that type
with nothing else.

Fixes: #4262
Change-Id: I02149e8a1ba1e7336149e962939b07ae0df83c6b

2 files changed, 24 insertions, 7 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 61e26b003..a8bd1de33 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -4270,6 +4270,14 @@ class GenericTypeCompiler(TypeCompiler):
 
 
 class StrSQLTypeCompiler(GenericTypeCompiler):
+    def process(self, type_, **kw):
+        try:
+            _compiler_dispatch = type_._compiler_dispatch
+        except AttributeError:
+            return self._visit_unknown(type_, **kw)
+        else:
+            return _compiler_dispatch(self, **kw)
+
     def __getattr__(self, key):
         if key.startswith("visit_"):
             return self._visit_unknown
@@ -4277,7 +4285,21 @@ class StrSQLTypeCompiler(GenericTypeCompiler):
             raise AttributeError(key)
 
     def _visit_unknown(self, type_, **kw):
-        return "%s" % type_.__class__.__name__
+        if type_.__class__.__name__ == type_.__class__.__name__.upper():
+            return type_.__class__.__name__
+        else:
+            return repr(type_)
+
+    def visit_null(self, type_, **kw):
+        return "NULL"
+
+    def visit_user_defined(self, type_, **kw):
+        try:
+            get_col_spec = type_.get_col_spec
+        except AttributeError:
+            return repr(type_)
+        else:
+            return get_col_spec(**kw)
 
 
 class IdentifierPreparer(object):
diff --git a/lib/sqlalchemy/sql/type_api.py b/lib/sqlalchemy/sql/type_api.py
index 2d23c56e1..1284ef515 100644
--- a/lib/sqlalchemy/sql/type_api.py
+++ b/lib/sqlalchemy/sql/type_api.py
@@ -626,12 +626,7 @@ class TypeEngine(Traversible):
     @util.preload_module("sqlalchemy.engine.default")
     def _default_dialect(self):
         default = util.preloaded.engine_default
-        if self.__class__.__module__.startswith("sqlalchemy.dialects"):
-            tokens = self.__class__.__module__.split(".")[0:3]
-            mod = ".".join(tokens)
-            return getattr(__import__(mod).dialects, tokens[-1]).dialect()
-        else:
-            return default.DefaultDialect()
+        return default.StrCompileDialect()
 
     def __str__(self):
         if util.py2k: