cl-symbol-macrolet: Fix recent regression

The recent fix for bug#57397 introduced a regression, breaking
the `cl-lib-symbol-macrolet-hide` test.  It turned out that the
origin of the problem was that `gv.el` uses `macroexpand-1` which
does not (can't) use `macroexpand` but `cl-symbol-macrolet` failed
to advise `macroexpand-1` the way it advised `macroexpand`.

To fix this, we change `cl-symbol-macrolet` so it advises both, and we
do that with a new `macroexpand` advice which delegates the bulk of
the work to `macroexpand-1`.

Along the way, I bumped into another bug in the interaction between
`cl-letf` and `cl-symbol-macrolet`, which I tried to fix in `cl-letf`.

I hear the war on `cl-symbol-macrolet` was a failure.
Maybe ... just say no?

* lisp/emacs-lisp/cl-macs.el (cl--sm-macroexpand-1): New function,
extracted from `cl--sm-macroexpand`.
(cl--sm-macroexpand): Rewrite completely.
(cl-symbol-macrolet): Advise both `macroexpand` and `macroexpand-1`.
(cl--letf): Don't use the "simple variable" code for symbol macros.

* test/lisp/emacs-lisp/cl-lib-tests.el (cl-lib-symbol-macrolet-hide):
Revert last change because the test was right.

* test/lisp/emacs-lisp/cl-macs-tests.el
(cl-macs-test--symbol-macrolet): Add a test case.

2 files changed, 8 insertions, 4 deletions

diff --git a/test/lisp/emacs-lisp/cl-lib-tests.el b/test/lisp/emacs-lisp/cl-lib-tests.el
index 8d2b187e33a..b19494af746 100644
--- a/test/lisp/emacs-lisp/cl-lib-tests.el
+++ b/test/lisp/emacs-lisp/cl-lib-tests.el
@@ -511,9 +511,6 @@
 
 
 (ert-deftest cl-lib-symbol-macrolet-hide ()
-  :expected-result :failed
-  ;; FIXME -- it's unclear what the semantics here should be, but
-  ;; 2dd1c2ab19f7fb99ecee flipped them.
   ;; bug#26325, bug#26073
   (should (equal (let ((y 5))
                    (cl-symbol-macrolet ((x y))
diff --git a/test/lisp/emacs-lisp/cl-macs-tests.el b/test/lisp/emacs-lisp/cl-macs-tests.el
index 2a647e08305..68898720d9c 100644
--- a/test/lisp/emacs-lisp/cl-macs-tests.el
+++ b/test/lisp/emacs-lisp/cl-macs-tests.el
@@ -552,7 +552,14 @@ collection clause."
                          x)
                        x))
              (error err))
-           '(1 7 3))))
+           '(1 7 3)))
+  (should (equal
+           (let ((x (list 42)))
+             (cl-symbol-macrolet ((m (car x)))
+               (list m
+                     (cl-letf ((m 5)) m)
+                     m)))
+           '(42 5 42))))
 
 (ert-deftest cl-macs-loop-conditional-step-clauses ()
   "These tests failed under the initial fixes in #bug#29799."