Merge "Use UnsupportedCompilationError for no default compiler"

4 files changed, 49 insertions, 11 deletions

diff --git a/doc/build/changelog/unreleased_13/5836.rst b/doc/build/changelog/unreleased_13/5836.rst
new file mode 100644
index 000000000..0ddfb9a8d
--- /dev/null
+++ b/doc/build/changelog/unreleased_13/5836.rst
@@ -0,0 +1,13 @@
+.. change::
+    :tags: bug, ext
+    :tickets: 5836
+
+    Fixed issue where the stringification that is sometimes called when
+    attempting to generate the "key" for the ``.c`` collection on a selectable
+    would fail if the column were an unlabeled custom SQL construct using the
+    ``sqlalchemy.ext.compiler`` extension, and did not provide a default
+    compilation form; while this seems like an unusual case, it can get invoked
+    for some ORM scenarios such as when the expression is used in an "order by"
+    in combination with joined eager loading.  The issue is that the lack of a
+    default compiler function was raising :class:`.CompileError` and not
+    :class:`.UnsupportedCompilationError`.
diff --git a/lib/sqlalchemy/exc.py b/lib/sqlalchemy/exc.py
index b031c1610..08b1bb060 100644
--- a/lib/sqlalchemy/exc.py
+++ b/lib/sqlalchemy/exc.py
@@ -179,10 +179,10 @@ class UnsupportedCompilationError(CompileError):
 
     code = "l7de"
 
-    def __init__(self, compiler, element_type):
+    def __init__(self, compiler, element_type, message=None):
         super(UnsupportedCompilationError, self).__init__(
-            "Compiler %r can't render element of type %s"
-            % (compiler, element_type)
+            "Compiler %r can't render element of type %s%s"
+            % (compiler, element_type, ": %s" % message if message else "")
         )
 
 
diff --git a/lib/sqlalchemy/ext/compiler.py b/lib/sqlalchemy/ext/compiler.py
index 5a31173ec..47fb6720b 100644
--- a/lib/sqlalchemy/ext/compiler.py
+++ b/lib/sqlalchemy/ext/compiler.py
@@ -425,9 +425,11 @@ def compiles(class_, *specs):
                         return existing_dispatch(element, compiler, **kw)
                     except exc.UnsupportedCompilationError as uce:
                         util.raise_(
-                            exc.CompileError(
-                                "%s construct has no default "
-                                "compilation handler." % type(element)
+                            exc.UnsupportedCompilationError(
+                                compiler,
+                                type(element),
+                                message="%s construct has no default "
+                                "compilation handler." % type(element),
                             ),
                             from_=uce,
                         )
@@ -476,9 +478,11 @@ class _dispatcher(object):
                 fn = self.specs["default"]
             except KeyError as ke:
                 util.raise_(
-                    exc.CompileError(
-                        "%s construct has no default "
-                        "compilation handler." % type(element)
+                    exc.UnsupportedCompilationError(
+                        compiler,
+                        type(element),
+                        message="%s construct has no default "
+                        "compilation handler." % type(element),
                     ),
                     replace_context=ke,
                 )
diff --git a/test/ext/test_compiler.py b/test/ext/test_compiler.py
index d011417d7..c10e27180 100644
--- a/test/ext/test_compiler.py
+++ b/test/ext/test_compiler.py
@@ -151,13 +151,33 @@ class UserDefinedTest(fixtures.TestBase, AssertsCompiledSQL):
             return "mythingy"
 
         assert_raises_message(
-            exc.CompileError,
+            exc.UnsupportedCompilationError,
             "<class 'test.ext.test_compiler..*MyThingy'> "
             "construct has no default compilation handler.",
             str,
             MyThingy(),
         )
 
+    def test_no_default_proxy_generation(self):
+        class my_function(FunctionElement):
+            name = "my_function"
+            type = Numeric()
+
+        @compiles(my_function, "sqlite")
+        def sqlite_my_function(element, compiler, **kw):
+            return "my_function(%s)" % compiler.process(element.clauses, **kw)
+
+        t1 = table("t1", column("q"))
+        stmt = select(my_function(t1.c.q))
+
+        self.assert_compile(
+            stmt,
+            "SELECT my_function(t1.q) AS my_function_1 FROM t1",
+            dialect="sqlite",
+        )
+
+        eq_(stmt.selected_columns.keys(), [stmt._raw_columns[0].anon_label])
+
     def test_no_default_message(self):
         class MyThingy(ClauseElement):
             pass
@@ -167,7 +187,8 @@ class UserDefinedTest(fixtures.TestBase, AssertsCompiledSQL):
             return "mythingy"
 
         assert_raises_message(
-            exc.CompileError,
+            exc.UnsupportedCompilationError,
+            "Compiler .*StrSQLCompiler.* can't .* "
             "<class 'test.ext.test_compiler..*MyThingy'> "
             "construct has no default compilation handler.",
             str,