Raise proper error on anonymous composite input (tuple arguments) (#664)

Currently asyncpg would crash with an arcane "could not resolve query
result and/or argument types in 6 attempts", which isn't helpful.  Do
the right thing by raising an `UnsupportedClientFeatureError`
explicitly instead.

Fixes #476.

asyncpg/exceptions/_base.py

@@ -210,6 +210,15 @@ def __init__(self, msg, *, detail=None, hint=None):
         InterfaceMessage.__init__(self, detail=detail, hint=hint)
         Exception.__init__(self, msg)
 
+    def with_msg(self, msg):
+        return type(self)(
+            msg,
+            detail=self.detail,
+            hint=self.hint,
+        ).with_traceback(
+            self.__traceback__
+        )
+
 
 class DataError(InterfaceError, ValueError):
     """An error caused by invalid query input."""

asyncpg/protocol/codecs/record.pyx

@@ -51,9 +51,20 @@ cdef anonymous_record_decode(ConnectionSettings settings, FRBuffer *buf):
     return result
 
 
+cdef anonymous_record_encode(ConnectionSettings settings, WriteBuffer buf, obj):
+    raise exceptions.UnsupportedClientFeatureError(
+        'input of anonymous composite types is not supported',
+        hint=(
+            'Consider declaring an explicit composite type and '
+            'using it to cast the argument.'
+        ),
+        detail='PostgreSQL does not implement anonymous composite type input.'
+    )
+
+
 cdef init_record_codecs():
     register_core_codec(RECORDOID,
-                        <encode_func>NULL,
+                        <encode_func>anonymous_record_encode,
                         <decode_func>anonymous_record_decode,
                         PG_FORMAT_BINARY)
 

asyncpg/protocol/prepared_stmt.pyx

@@ -156,9 +156,11 @@ cdef class PreparedStatementState:
                 except (AssertionError, exceptions.InternalClientError):
                     # These are internal errors and should raise as-is.
                     raise
-                except exceptions.InterfaceError:
-                    # This is already a descriptive error.
-                    raise
+                except exceptions.InterfaceError as e:
+                    # This is already a descriptive error, but annotate
+                    # with argument name for clarity.
+                    raise e.with_msg(
+                        f'query argument ${idx + 1}: {e.args[0]}') from None
                 except Exception as e:
                     # Everything else is assumed to be an encoding error
                     # due to invalid input.

tests/test_codecs.py

@@ -892,6 +892,13 @@ async def test_composites(self):
 
         self.assertEqual(res, (None, 1234, '5678', (42, '42')))
 
+        with self.assertRaisesRegex(
+            asyncpg.UnsupportedClientFeatureError,
+            'query argument \\$1: input of anonymous '
+            'composite types is not supported',
+        ):
+            await self.con.fetchval("SELECT (1, 'foo') = $1", (1, 'foo'))
+
         try:
             st = await self.con.prepare('''
                 SELECT ROW(