percent sign escaping in literal binds

[Mike Bayer]

from sqlalchemy import *

e = create_engine("mysql://scott:tiger@localhost/test", echo=True)

s = select([literal("hi % there")])


compiled = s.compile(
    dialect=e.dialect,
    compile_kwargs=dict(literal_binds=True)
)

assert e.scalar(str(compiled)) == "hi % there"

related to #4052 as that makes use of literals. in addition, comment support should be consistent about its use of literal binds vs. other ad-hoc systems

[Mike Bayer]

https://gerrit.sqlalchemy.org/489

[Mike Bayer]

Apply percent sign escaping to literal binds, comments

Fixed bug in new percent-sign support (e.g. 3740) where a bound parameter rendered with literal_binds would fail to escape percent-signs for relevant dialects. In addition, ensured new table / column comment support feature also fully makes use of literal-rendered parameters so that this percent sign support takes place with table / column comment DDL as well, allowing percent sign support for the mysql / psycopg2 backends that require escaping of percent signs.

Change-Id: Ia4136a300933e9bc6a01a7b9afd5c7b9a3fee4e3 Fixes: #4054 Fixes: #4052

→ <<cset 2392ae1900f1>>