From 68709fe93a2b023d03b107473438e791036b31ef Mon Sep 17 00:00:00 2001
From: Henrik Lissner <henrik@lissner.net>
Date: Thu, 14 May 2020 22:32:03 -0400
Subject: [PATCH] Fix letf! sometimes losing letf binds

When expanding:

  (quiet! ...)

You'd expect (simplified for explanation):

  (letf! ((standard-output ...)
         ((symbol-function #'message) ...)
         ((symbol-function #'load-file) ...)
         ((symbol-function #'write-region) ...))
    ...)

But instead get:

  (letf! ((standard-output ...))
    ;; where'd the other binds go?
    ...)

This was due to data-loss caused by nreverse's destructive mutation of
the given bindings.

Also: silences byte-compiler complaining about unused bindings.
---
 core/core-lib.el | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/core/core-lib.el b/core/core-lib.el
index 1e3dc6244..adabe49c6 100644
--- a/core/core-lib.el
+++ b/core/core-lib.el
@@ -210,20 +210,21 @@ the same name, for use with `funcall' or `apply'. ARGLIST and BODY are as in
   (setq body (macroexp-progn body))
   (when (memq (car bindings) '(defun defmacro))
     (setq bindings (list bindings)))
-  (dolist (binding (nreverse bindings) body)
+  (dolist (binding (reverse bindings) (macroexpand body))
     (let ((type (car binding))
           (rest (cdr binding)))
       (setq
        body (pcase type
               (`defmacro `(cl-macrolet ((,(car rest) ,(cadr rest) ,@(cddr rest))) ,body))
               (`defun `(cl-letf* ((,(car rest) (symbol-function #',(car rest)))
-                                   ((symbol-function #',(car rest))
-                                    (lambda ,(cadr rest) ,@(cddr rest))))
-                          ,body))
+                                  ((symbol-function #',(car rest))
+                                   (lambda ,(cadr rest) ,@(cddr rest))))
+                         (ignore ,(car rest))
+                         ,body))
               (_
                (when (eq (car-safe type) 'function)
-                 (setq type `(symbol-function ,type)))
-               `(cl-letf ((,type ,@rest)) ,body)))))))
+                 (setq type (list 'symbol-function type)))
+               (list 'cl-letf (list (cons type rest)) body)))))))
 
 (defmacro quiet! (&rest forms)
   "Run FORMS without generating any output.