2 files changed, 20 insertions, 10 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 16d17821b78..08c7f8a4dd6 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -4321,15 +4321,21 @@ whose matches are to be replaced.  If these variables are nil (which
 is the default), 'query-replace' and 'query-replace-regexp' take the
 default value from the previous FROM-TO pair.
 
----
-** New user option 'pp-use-max-width'.
-If non-nil, 'pp' will attempt to limit the line length when formatting
-long lists and vectors.
+** Lisp pretty-printer ('pp')
 
 ---
-** New function 'pp-emacs-lisp-code'.
+*** New function 'pp-emacs-lisp-code'.
 'pp' formats general Lisp sexps.  This function does much the same,
-but applies formatting rules appropriate for Emacs Lisp code.
+but applies formatting rules appropriate for Emacs Lisp code.  Note
+that this could currently be quite slow, and is thus appropriate only
+for relatively small code fragments.
+
+---
+*** New user option 'pp-use-max-width'.
+If non-nil, 'pp' and all 'pp-*' commands that format the results, will
+attempt to limit the line length when formatting long lists and
+vectors.  This uses 'pp-emacs-lisp-code', and thus could be slow for
+large lists.
 
 +++
 ** New function 'file-has-changed-p'.
diff --git a/lisp/emacs-lisp/pp.el b/lisp/emacs-lisp/pp.el
index ebda37419f7..e6e3cd6c6f4 100644
--- a/lisp/emacs-lisp/pp.el
+++ b/lisp/emacs-lisp/pp.el
@@ -47,7 +47,9 @@ Otherwise this should be a number."
 
 (defcustom pp-use-max-width nil
   "If non-nil, `pp'-related functions will try to fold lines.
-The target width is given by the `pp-max-width' variable."
+The target width is given by the `pp-max-width' variable.
+Note that this could slow down `pp' considerably when formatting
+large lists."
   :type 'boolean
   :version "29.1")
 
@@ -162,14 +164,15 @@ Also add the value to the front of the list in the variable `values'."
   (message "Evaluating...")
   (let ((result (eval expression lexical-binding)))
     (values--store-value result)
-    (pp-display-expression result "*Pp Eval Output*")))
+    (pp-display-expression result "*Pp Eval Output*" pp-use-max-width)))
 
 ;;;###autoload
 (defun pp-macroexpand-expression (expression)
   "Macroexpand EXPRESSION and pretty-print its value."
   (interactive
    (list (read--expression "Macroexpand: ")))
-  (pp-display-expression (macroexpand-1 expression) "*Pp Macroexpand Output*"))
+  (pp-display-expression (macroexpand-1 expression) "*Pp Macroexpand Output*"
+                         pp-use-max-width))
 
 (defun pp-last-sexp ()
   "Read sexp before point.  Ignore leading comment characters."
@@ -219,7 +222,8 @@ Ignores leading comment characters."
 ;;;###autoload
 (defun pp-emacs-lisp-code (sexp)
   "Insert SEXP into the current buffer, formatted as Emacs Lisp code.
-Use the `pp-max-width' variable to control the desired line length."
+Use the `pp-max-width' variable to control the desired line length.
+Note that this could be slow for large SEXPs."
   (require 'edebug)
   (let ((obuf (current-buffer)))
     (with-temp-buffer