fix construct_params() for render_postcompile; add new API

The :meth:`.SQLCompiler.construct_params` method, as well as the
:attr:`.SQLCompiler.params` accessor, will now return the
exact parameters that correspond to a compiled statement that used
the ``render_postcompile`` parameter to compile.   Previously,
the method returned a parameter structure that by itself didn't correspond
to either the original parameters or the expanded ones.

Passing a new dictionary of parameters to
:meth:`.SQLCompiler.construct_params` for a :class:`.SQLCompiler` that was
constructed with ``render_postcompile`` is now disallowed; instead, to make
a new SQL string and parameter set for an alternate set of parameters, a
new method :meth:`.SQLCompiler.construct_expanded_state` is added which
will produce a new expanded form for the given parameter set, using the
:class:`.ExpandedState` container which includes a new SQL statement
and new parameter dictionary, as well as a positional parameter tuple.

Fixes: #6114
Change-Id: I9874905bb90f86799b82b244d57369558b18fd93

1 files changed, 23 insertions, 3 deletions

diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index 790a72ec8..5adda0dad 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -636,10 +636,30 @@ class AssertsCompiledSQL:
         eq_(cc, result, "%r != %r on dialect %r" % (cc, result, dialect))
 
         if checkparams is not None:
-            eq_(c.construct_params(params), checkparams)
+            if render_postcompile:
+                expanded_state = c.construct_expanded_state(
+                    params, escape_names=False
+                )
+                eq_(expanded_state.parameters, checkparams)
+            else:
+                eq_(c.construct_params(params), checkparams)
         if checkpositional is not None:
-            p = c.construct_params(params, escape_names=False)
-            eq_(tuple([p[x] for x in c.positiontup]), checkpositional)
+            if render_postcompile:
+                expanded_state = c.construct_expanded_state(
+                    params, escape_names=False
+                )
+                eq_(
+                    tuple(
+                        [
+                            expanded_state.parameters[x]
+                            for x in expanded_state.positiontup
+                        ]
+                    ),
+                    checkpositional,
+                )
+            else:
+                p = c.construct_params(params, escape_names=False)
+                eq_(tuple([p[x] for x in c.positiontup]), checkpositional)
         if check_prefetch is not None:
             eq_(c.prefetch, check_prefetch)
         if check_literal_execute is not None: