add informative exception context for literal render

An informative re-raise is now thrown in the case where any "literal
bindparam" render operation fails, indicating the value itself and
the datatype in use, to assist in debugging when literal params
are being rendered in a statement.

Fixes: #8800
Change-Id: Id658f8b03359312353ddbb0c7563026239579f7b

3 files changed, 25 insertions, 10 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 97397e9cf..9a00afc91 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -63,6 +63,7 @@ from . import roles
 from . import schema
 from . import selectable
 from . import sqltypes
+from . import util as sql_util
 from ._typing import is_column_element
 from ._typing import is_dml
 from .base import _from_objects
@@ -1530,7 +1531,8 @@ class SQLCompiler(Compiled):
                 replacement_expressions[
                     escaped_name
                 ] = self.render_literal_bindparam(
-                    parameter, render_literal_value=value
+                    parameter,
+                    render_literal_value=value,
                 )
                 continue
 
@@ -3154,10 +3156,22 @@ class SQLCompiler(Compiled):
 
         processor = type_._cached_literal_processor(self.dialect)
         if processor:
-            return processor(value)
+            try:
+                return processor(value)
+            except Exception as e:
+                raise exc.CompileError(
+                    f"Could not render literal value "
+                    f'"{sql_util._repr_single_value(value)}" '
+                    f"with datatype "
+                    f"{type_}; see parent stack trace for "
+                    "more detail."
+                ) from e
+
         else:
-            raise NotImplementedError(
-                "Don't know how to literal-quote value %r" % value
+            raise exc.CompileError(
+                f"No literal value renderer is available for literal value "
+                f'"{sql_util._repr_single_value(value)}" '
+                f"with datatype {type_}"
             )
 
     def _truncate_bindparam(self, bindparam):
diff --git a/lib/sqlalchemy/sql/sqltypes.py b/lib/sqlalchemy/sql/sqltypes.py
index 414ff03c3..b98a16b6f 100644
--- a/lib/sqlalchemy/sql/sqltypes.py
+++ b/lib/sqlalchemy/sql/sqltypes.py
@@ -3381,12 +3381,7 @@ class NullType(TypeEngine[None]):
     _isnull = True
 
     def literal_processor(self, dialect):
-        def process(value):
-            raise exc.CompileError(
-                "Don't know how to render literal SQL value: %r" % (value,)
-            )
-
-        return process
+        return None
 
     class Comparator(TypeEngine.Comparator[_T]):
         __slots__ = ()
diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index 55c6a35f8..1f9944529 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -581,6 +581,12 @@ class _repr_base:
         return rep
 
 
+def _repr_single_value(value):
+    rp = _repr_base()
+    rp.max_chars = 300
+    return rp.trunc(value)
+
+
 class _repr_row(_repr_base):
     """Provide a string view of a row."""