master c21103bb76e: Explicitly disallow named-let in code using dynamic binding

[Mattias Engdegård]

branch: master
commit c21103bb76e6997064917b23b8fdfbf0a1149375
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Explicitly disallow named-let in code using dynamic binding
    
    There is no point in permitting named-let to be used in dynbound code;
    our code transforms are simply not valid in that context, and it's not
    worth the trouble to make it work (to the extent that it is at all
    possible). (Bug#59576)
    
    * lisp/emacs-lisp/subr-x.el (named-let):
    Error if used with dynamic binding.
    * doc/lispref/variables.texi (Local Variables): Amend manual.
---
 doc/lispref/variables.texi | 4 ++--
 lisp/emacs-lisp/subr-x.el  | 6 +++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index 55761ff75e2..93930d17587 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -351,8 +351,8 @@ A function call is in the tail position if it's the very 
last thing
 done so that the value returned by the call is the value of @var{body}
 itself, as is the case in the recursive call to @code{sum} above.
 
-@strong{Warning:} @code{named-let} works as expected only when
-lexical-binding is enabled.  @xref{Lexical Binding}.
+@code{named-let} can only be used when lexical-binding is enabled.
+@xref{Lexical Binding}.
 @end defspec
 
   Here is a complete list of the other facilities that create local
diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 78dc58e0bcd..572822351b1 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -312,9 +312,13 @@ it makes no sense to convert it to a string using
 Like `let', bind variables in BINDINGS and then evaluate BODY,
 but with the twist that BODY can evaluate itself recursively by
 calling NAME, where the arguments passed to NAME are used
-as the new values of the bound variables in the recursive invocation."
+as the new values of the bound variables in the recursive invocation.
+
+This construct can only be used with lexical binding."
   (declare (indent 2) (debug (symbolp (&rest (symbolp form)) body)))
   (require 'cl-lib)
+  (unless lexical-binding
+    (error "`named-let' requires lexical binding"))
   (let ((fargs (mapcar (lambda (b) (if (consp b) (car b) b)) bindings))
         (aargs (mapcar (lambda (b) (if (consp b) (cadr b))) bindings)))
     ;; According to the Scheme semantics of named let, `name' is not in scope