Subject: bug#31792: 27.0.50; Regression in #'labels, recent versions

From: Noam Postavsky <[email-masked]>
Date: Thu, 14 Jun 2018 00:13:50 -0400

Stefan Monnier <[email-masked]> writes:

>> +Bind the function cells of symbols within FORM.
>
> I think this is wrong: it makes it sound like it does `fset`, which
> is what CL's `flet` did, but not what `cl-flet` does.
> If you look at the implementation, you'll see that it doesn't touch any
> "function cell".

Hmm, the manual page says something similar:

 -- Macro: cl-flet (bindings...) forms...
     This form establishes `let'-style bindings on the function cells
     of symbols rather than on the value cells.

It also wrongly claims that (quote FUNC) would work:

     A "reference" to a function name is either a call to that
     function, or a use of its name quoted by `quote' or `function' to
                                              ^^^^^^^
     be passed on to, say, `mapcar'.

Perhaps both of those are leftovers from the original `flet'
description.  How about this:

>From f83d79ca2707f4bbe0bc1b0a74ee78d7cc64cbe5 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <[email-masked]>
Date: Tue, 12 Jun 2018 18:41:46 -0400
Subject: [PATCH v3] Fix #'fun handling inside `labels' (Bug#31792)

* lisp/emacs-lisp/cl.el (labels): Apply the equivalent of the
cl-labels change from 2015-01-16 "* lisp/emacs-lisp/cl-macs.el: Fix
last change".
* test/lisp/emacs-lisp/cl-tests.el (labels-function-quoting): New
test.
* lisp/emacs-lisp/cl-macs.el (cl-flet, cl-labels): Improve docstring,
link to relevant manual page.
* doc/misc/cl.texi (Function Bindings): Don't imply that function
cells of symbols are modified by cl-flet.  Don't claim that cl-flet or
cl-labels affect references of the form (quote FUNC).
---
 doc/misc/cl.texi                 | 23 ++++++++++-------------
 lisp/emacs-lisp/cl-macs.el       | 17 ++++++++++++-----
 lisp/emacs-lisp/cl.el            |  7 +++++--
 test/lisp/emacs-lisp/cl-tests.el | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+), 20 deletions(-)
 create mode 100644 test/lisp/emacs-lisp/cl-tests.el

diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index bf85b00e93..553b935b1e 100644
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -1299,17 +1299,18 @@ Function Bindings
 of variables.
 
 @defmac cl-flet (bindings@dots{}) forms@dots{}
-This form establishes @code{let}-style bindings on the function
-cells of symbols rather than on the value cells.  Each @var{binding}
-must be a list of the form @samp{(@var{name} @var{arglist}
-@var{forms}@dots{})}, which defines a function exactly as if
-it were a @code{cl-defun} form.  The function @var{name} is defined
-accordingly but only within the body of the @code{cl-flet}, hiding any external
-definition if applicable.
+This form establishes @code{let}-style bindings for functions rather
+than values.  Each @var{binding} must be a list of the form
+@samp{(@var{name} @var{arglist} @var{body}@dots{})}.  Within
+@var{forms}, any reference to the function @var{name} uses the local
+definition instead of the global one.
+
+A ``reference'' to a function name is either a call to that function,
+or a use of its name quoted by @code{function} to be passed on to,
+say, @code{mapcar}.
 
 The bindings are lexical in scope.  This means that all references to
-the named functions must appear physically within the body of the
-@code{cl-flet} form.
+the named functions must appear physically within @var{forms}.
 
 Functions defined by @code{cl-flet} may use the full Common Lisp
 argument notation supported by @code{cl-defun}; also, the function
@@ -1336,10 +1337,6 @@ Function Bindings
 the functions themselves.  Thus, @code{cl-labels} can define
 local recursive functions, or mutually-recursive sets of functions.
 
-A ``reference'' to a function name is either a call to that
-function, or a use of its name quoted by @code{quote} or
-@code{function} to be passed on to, say, @code{mapcar}.
-
 Note that the @file{cl.el} version of this macro behaves slightly
 differently.  @xref{Obsolete Macros}.
 @end defmac
diff --git a/lisp/emacs-lisp/cl-macs.el b/lisp/emacs-lisp/cl-macs.el
index 9c47ceae18..0854e665b9 100644
--- a/lisp/emacs-lisp/cl-macs.el
+++ b/lisp/emacs-lisp/cl-macs.el
@@ -1964,13 +1964,16 @@ cl--labels-convert
 ;;;###autoload
 (defmacro cl-flet (bindings &rest body)
   "Make local function definitions.
-Like `cl-labels' but the definitions are not recursive.
-Each binding can take the form (FUNC EXP) where
+Each definition can take the form (FUNC EXP) where
 FUNC is the function name, and EXP is an expression that returns the
 function value to which it should be bound, or it can take the more common
 form \(FUNC ARGLIST BODY...) which is a shorthand
 for (FUNC (lambda ARGLIST BODY)).
 
+FUNC is defined only within FORM, not BODY, so you can't write
+recursive function definitions.  Use `cl-labels' for that.  See
+info node `(cl) Function Bindings' for details.
+
 \(fn ((FUNC ARGLIST BODY...) ...) FORM...)"
   (declare (indent 1) (debug ((&rest (cl-defun)) cl-declarations body)))
   (let ((binds ()) (newenv macroexpand-all-environment))
@@ -2012,9 +2015,13 @@ cl-flet*
 
 ;;;###autoload
 (defmacro cl-labels (bindings &rest body)
-  "Make temporary function bindings.
-The bindings can be recursive and the scoping is lexical, but capturing them
-in closures will only work if `lexical-binding' is in use.
+    "Make local (recursive) function definitions.
+Each definition can take the form (FUNC ARGLIST BODY...) where
+FUNC is the function name, ARGLIST its arguments, and BODY the
+forms of the function body.  FUNC is defined in any BODY, as well
+as FORM, so you can write recursive and mutually recursive
+function definitions.  See info node `(cl) Function Bindings' for
+details.
 
 \(fn ((FUNC ARGLIST BODY...) ...) FORM...)"
   (declare (indent 1) (debug cl-flet))
diff --git a/lisp/emacs-lisp/cl.el b/lisp/emacs-lisp/cl.el
index d53c8e0bbc..f6643158d2 100644
--- a/lisp/emacs-lisp/cl.el
+++ b/lisp/emacs-lisp/cl.el
@@ -466,9 +466,12 @@ labels
 	(push var sets)
 	(push (cons (car binding)
                     `(lambda (&rest cl-labels-args)
-                       (cl-list* 'funcall ',var
-                                 cl-labels-args)))
+                       (if (eq (car cl-labels-args) cl--labels-magic)
+                           (list cl--labels-magic ',var)
+                         (cl-list* 'funcall ',var cl-labels-args))))
               newenv)))
+    ;; `lexical-let' adds `cl--function-convert' (which calls
+    ;; `cl--labels-convert') as a macroexpander for `function'.
     (macroexpand-all `(lexical-let ,vars (setq ,@sets) ,@body) newenv)))
 
 ;; Generalized variables are provided by gv.el, but some details are
diff --git a/test/lisp/emacs-lisp/cl-tests.el b/test/lisp/emacs-lisp/cl-tests.el
new file mode 100644
index 0000000000..b673822cd9
--- /dev/null
+++ b/test/lisp/emacs-lisp/cl-tests.el
@@ -0,0 +1,35 @@
+;;; cl-tests.el --- tests for emacs-lisp/cl.el  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2018 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; This program is free software: you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation, either version 3 of the
+;; License, or (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see `https://www.gnu.org/licenses/'.
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'cl)
+(require 'ert)
+
+
+
+(ert-deftest labels-function-quoting ()
+  "Test that #'foo does the right thing in `labels'." ; Bug#31792.
+  (should (eq (funcall (labels ((foo () t))
+                         #'foo))
+              t)))
+
+;;; cl-tests.el ends here
-- 
2.11.0