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
(cherry picked from commit c7baf6e0aa624c9378c3bc3c4923d1e188d62dc9)

1 files changed, 25 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index a7232f096..611cd1821 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -38,6 +38,7 @@ from . import operators
 from . import schema
 from . import selectable
 from . import sqltypes
+from . import util as sql_util
 from .base import NO_ARG
 from .base import prefix_anon_map
 from .elements import quoted_name
@@ -1216,7 +1217,8 @@ class SQLCompiler(Compiled):
                 replacement_expressions[
                     escaped_name
                 ] = self.render_literal_bindparam(
-                    parameter, render_literal_value=value
+                    parameter,
+                    render_literal_value=value,
                 )
                 continue
 
@@ -2590,10 +2592,29 @@ class SQLCompiler(Compiled):
 
         processor = type_._cached_literal_processor(self.dialect)
         if processor:
-            return processor(value)
+            try:
+                return processor(value)
+            except Exception as e:
+                util.raise_(
+                    exc.CompileError(
+                        "Could not render literal value "
+                        '"%s" '
+                        "with datatype "
+                        "%s; see parent stack trace for "
+                        "more detail."
+                        % (
+                            sql_util._repr_single_value(value),
+                            type_,
+                        )
+                    ),
+                    from_=e,
+                )
+
         else:
-            raise NotImplementedError(
-                "Don't know how to literal-quote value %r" % value
+            raise exc.CompileError(
+                "No literal value renderer is available for literal value "
+                '"%s" with datatype %s'
+                % (sql_util._repr_single_value(value), type_)
             )
 
     def _truncate_bindparam(self, bindparam):