bug#54536: 29.0.50; Improve ERC's handling of multiline prompt input

From bb190883389de0bdcdfa39bfdbb5d8953bf115fd Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email protected]>
Date: Wed, 27 Apr 2022 04:33:06 -0700
Subject: [PATCH 0/4] *** NOT A PATCH ***

*** BLURB HERE ***

F. Jason Park (4):
  Fix regression in erc-send-input-line
  Add some ERC test helpers
  Improve ERC's handling of multiline prompt input
  Optionally prevent sending multiline input in ERC

 lisp/erc/erc.el            | 195 ++++++++++++++++++++++------
 test/lisp/erc/erc-tests.el | 259 +++++++++++++++++++++++++++++++++++--
 2 files changed, 402 insertions(+), 52 deletions(-)

Interdiff:
diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 472c103ee4..8e96dd30c4 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -224,6 +224,20 @@ erc-send-whitespace-lines
   :group 'erc
   :type 'boolean)
 
+(defcustom erc-inhibit-multiline-input nil
+  "Conditionally disallow input consisting of multiple lines.
+Issue an error when the number of input lines submitted for sending
+exceeds this value."
+  :package-version '(ERC . "5.4.1") ; FIXME match to next release
+  :group 'erc
+  :type '(choice integer boolean))
+
+(defcustom erc-ask-about-multiline-input nil
+  "Ask to ignore `erc-inhibit-multiline-input' when tripped."
+  :package-version '(ERC . "5.4.1") ; FIXME match to next release
+  :group 'erc
+  :type 'boolean)
+
 (defcustom erc-hide-prompt nil
   "If non-nil, do not display the prompt for commands.
 
@@ -1054,10 +1068,16 @@ erc-pre-send-functions
   :type 'hook
   :version "27.1")
 
-(defcustom erc-pre-send-split-functions '(erc-discard-trailing-multiline-nulls)
+;; This is being auditioned for possible exporting (as a custom
+;; option).  Likewise for (public versions of) `erc--input-split' and
+;; `erc--discard-trailing-multiline-nulls'.  If unneeded, we'll just
+;; run the latter on the input after `erc-pre-send-functions', and
+;; remove this hook and the struct completely.
+
+(defvar erc--pre-send-split-functions '(erc--discard-trailing-multiline-nulls)
   "Special hook for modifying individual lines in multiline prompt input.
-The functions are called with one argument, an `erc-input-split' struct,
-which they can optionally modify.
+The functions are called with one argument, an `erc--input-split'
+struct, which they can optionally modify.
 
 The struct has five slots:
 
@@ -1068,10 +1088,7 @@ erc-pre-send-split-functions
   `cmdp': Whether to interpret the input as a command, like /ignore.
 
 The `string' field is effectively read-only.  When `cmdp' is non-nil,
-all but the first line will be discarded."
-  :group 'erc
-  :type 'hook
-  :package-version '(ERC . "5.4.1"))
+all but the first line will be discarded.")
 
 (defvar erc-insert-this t
   "Insert the text into the target buffer or not.
@@ -5573,61 +5590,77 @@ erc-accidental-paste-threshold-seconds
 
 (defvar erc--input-line-delim-regexp (rx (| (: (? ?\r) ?\n) ?\r)))
 
-(defun erc--blank-in-multiline-input-p (string)
-  "Detect whether STRING contains any blank lines.
-When `erc-send-whitespace-lines' is in effect, return nil if the input
-is multiline or the line is non-empty.  When `erc-send-whitespace-lines'
-is nil, return non-nil when any line is empty or consists of one or more
+(defun erc--blank-in-multiline-input-p (lines)
+  "Detect whether LINES contains a blank line.
+When `erc-send-whitespace-lines' is in effect, return nil if LINES is
+multiline or the first non-empty.  When `erc-send-whitespace-lines' is
+nil, return non-nil when any line is empty or consists of one or more
 spaces, tabs, or form-feeds."
   (catch 'return
-    (let ((lines (split-string string erc--input-line-delim-regexp)))
+    (let ((multilinep (cdr lines)))
       (dolist (line lines)
         (when (if erc-send-whitespace-lines
-                  (and (string= line "") (null (cdr lines)))
+                  (and (string-empty-p line) (not multilinep))
                 (string-match (rx bot (* (in " \t\f")) eot) line))
           (throw 'return t))))))
 
-(defun erc-discard-trailing-multiline-nulls (state)
+(defun erc--discard-trailing-multiline-nulls (state)
   "Ensure last line of `erc-input' STATE's string is non-null.
 But only when `erc-send-whitespace-lines' is non-nil."
   (when erc-send-whitespace-lines
     (when (string-match "[\r\n]+\\'" (erc-input-string state))
-      (setf (erc-input-split-lines state)
+      (setf (erc--input-split-lines state)
             (split-string (substring (erc-input-string state)
                                      0
                                      (match-beginning 0))
                           erc--input-line-delim-regexp)
-            (erc-input-split-cmdp state) nil))))
-
-(defun erc-check-prompt-input-for-multiline-blanks (string)
-  "Return non-nil when multiline prompt input has blank lines."
-  (when (erc--blank-in-multiline-input-p string)
+            (erc--input-split-cmdp state) nil))))
+
+(defun erc--check-prompt-input-for-excess-lines (_ lines)
+  "Return non-nil when trying to send too many LINES."
+  (when erc-inhibit-multiline-input
+    ;; Assume `erc--discard-trailing-multiline-nulls' is set to run
+    (let ((reversed (seq-drop-while #'string-empty-p (reverse lines)))
+          (max (if (eq erc-inhibit-multiline-input t)
+                   2
+                 erc-inhibit-multiline-input))
+          (seen 0)
+          msg)
+      (while (and (pop reversed) (< (cl-incf seen) max)))
+      (when (= seen max)
+        (setq msg (format "(exceeded by %d)" (1+ (length reversed))))
+        (unless (and erc-ask-about-multiline-input
+                     (y-or-n-p (concat "Send input " msg "?")))
+          (concat "Too many lines " msg))))))
+
+(defun erc--check-prompt-input-for-multiline-blanks (_ lines)
+  "Return non-nil when multiline prompt input has blank LINES."
+  (when (erc--blank-in-multiline-input-p lines)
     (if erc-warn-about-blank-lines
         "Blank line - ignoring..."
       'invalid)))
 
-(defun erc-check-prompt-input-for-point-in-bounds (_)
+(defun erc--check-prompt-input-for-point-in-bounds (_ _)
   "Return non-nil when point is before prompt."
   (when (< (point) (erc-beg-of-input-line))
     "Point is not in the input area"))
 
-(defun erc-check-prompt-input-for-running-process (string)
+(defun erc--check-prompt-input-for-running-process (string _)
   "Return non-nil unless in an active ERC server buffer."
   (unless (or (erc-server-buffer-live-p)
               (erc-command-no-process-p string))
     "ERC: No process running"))
 
-(defcustom erc-check-prompt-input-functions
-  '(erc-check-prompt-input-for-point-in-bounds
-    erc-check-prompt-input-for-multiline-blanks
-    erc-check-prompt-input-for-running-process)
+(defvar erc--check-prompt-input-functions
+  '(erc--check-prompt-input-for-point-in-bounds
+    erc--check-prompt-input-for-multiline-blanks
+    erc--check-prompt-input-for-running-process
+    erc--check-prompt-input-for-excess-lines)
   "Validators for user input typed at prompt.
-Called with latest input string submitted by user.  If any member
-returns non-nil, processing is abandoned and input is left untouched.
-When the returned value is a string, pass it to `erc-error'."
-  :package-version '(ERC . "5.4.1") ; FIXME increment upon publishing to ELPA
-  :group 'erc
-  :type 'hook)
+Called with latest input string submitted by user and the list of lines
+produced by splitting it.  If any member function returns non-nil,
+processing is abandoned and input is left untouched.  When the returned
+value is a string, pass it to `erc-error'.")
 
 (defun erc-send-current-line ()
   "Parse current line and send it to IRC."
@@ -5644,7 +5677,8 @@ erc-send-current-line
           (widen)
           (if-let* ((str (erc-user-input))
                     (msg (run-hook-with-args-until-success
-                          'erc-check-prompt-input-functions str)))
+                          'erc--check-prompt-input-functions str
+                          (split-string str erc--input-line-delim-regexp))))
               (when (stringp msg)
                 (erc-error msg))
             (let ((inhibit-read-only t)
@@ -5688,7 +5722,7 @@ erc-command-regexp
 (cl-defstruct erc-input
   string insertp sendp)
 
-(cl-defstruct (erc-input-split (:include erc-input))
+(cl-defstruct (erc--input-split (:include erc-input))
   lines cmdp)
 
 (defun erc-send-input (input &optional skip-ws-chk)
@@ -5697,7 +5731,8 @@ erc-send-input
 Return non-nil only if we actually send anything."
   ;; Handle different kinds of inputs
   (if (and (not skip-ws-chk)
-           (erc-check-prompt-input-for-multiline-blanks input))
+           (erc--check-prompt-input-for-multiline-blanks
+            input (split-string input erc--input-line-delim-regexp)))
       (when erc-warn-about-blank-lines
         (message "Blank line - ignoring...") ; compat
         (beep))
@@ -5720,7 +5755,7 @@ erc-send-input
 				  :insertp erc-insert-this
 				  :sendp erc-send-this))
       (run-hook-with-args 'erc-pre-send-functions state)
-      (setq state (make-erc-input-split
+      (setq state (make-erc--input-split
                    :string (erc-input-string state)
                    :insertp (erc-input-insertp state)
                    :sendp (erc-input-sendp state)
@@ -5728,11 +5763,11 @@ erc-send-input
                                         erc--input-line-delim-regexp)
                    :cmdp (string-match erc-command-regexp
                                        (erc-input-string state))))
-      (run-hook-with-args 'erc-pre-send-split-functions state)
+      (run-hook-with-args 'erc--pre-send-split-functions state)
       (when (and (erc-input-sendp state)
                  erc-send-this)
-        (let ((lines (erc-input-split-lines state)))
-          (if (and (erc-input-split-cmdp state) (not (cdr lines)))
+        (let ((lines (erc--input-split-lines state)))
+          (if (and (erc--input-split-cmdp state) (not (cdr lines)))
               (erc-process-input-line (concat (car lines) "\n") t nil)
             (dolist (line lines)
               (dolist (line (or (and erc-flood-protect (erc-split-line line))
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 3746f4862e..fa39f4fcc6 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -327,36 +327,41 @@ erc--input-line-delim-regexp
     (should (equal '("" "" "") (split-string "\n\r" p)))))
 
 (ert-deftest erc--blank-in-multiline-input-p ()
-  (ert-info ("With `erc-send-whitespace-lines'")
-    (let ((erc-send-whitespace-lines t))
-      (should (erc--blank-in-multiline-input-p ""))
-      (should-not (erc--blank-in-multiline-input-p "/msg a\n")) ; real /cmd
-      (should-not (erc--blank-in-multiline-input-p "a\n\nb")) ; "" allowed
-      (should-not (erc--blank-in-multiline-input-p "/msg a\n\nb")) ; non-/cmd
-      (should-not (erc--blank-in-multiline-input-p " "))
-      (should-not (erc--blank-in-multiline-input-p "\t"))
-      (should-not (erc--blank-in-multiline-input-p "a\nb"))
-      (should-not (erc--blank-in-multiline-input-p "a\n "))
-      (should-not (erc--blank-in-multiline-input-p "a\n \t"))
-      (should-not (erc--blank-in-multiline-input-p "a\n \f"))
-      (should-not (erc--blank-in-multiline-input-p "a\n \nb"))
-      (should-not (erc--blank-in-multiline-input-p "a\n \t\nb"))
-      (should-not (erc--blank-in-multiline-input-p "a\n \f\nb"))))
-
-  (should (erc--blank-in-multiline-input-p ""))
-  (should (erc--blank-in-multiline-input-p " "))
-  (should (erc--blank-in-multiline-input-p "\t"))
-  (should (erc--blank-in-multiline-input-p "a\n\nb"))
-  (should (erc--blank-in-multiline-input-p "a\n\nb"))
-  (should (erc--blank-in-multiline-input-p "a\n "))
-  (should (erc--blank-in-multiline-input-p "a\n \t"))
-  (should (erc--blank-in-multiline-input-p "a\n \f"))
-  (should (erc--blank-in-multiline-input-p "a\n \nb"))
-  (should (erc--blank-in-multiline-input-p "a\n \t\nb"))
-
-  (should-not (erc--blank-in-multiline-input-p "a\rb"))
-  (should-not (erc--blank-in-multiline-input-p "a\nb"))
-  (should-not (erc--blank-in-multiline-input-p "a\r\nb")))
+  (let ((check (lambda (s)
+                 (erc--blank-in-multiline-input-p
+                  (split-string s erc--input-line-delim-regexp)))))
+
+    (ert-info ("With `erc-send-whitespace-lines'")
+      (let ((erc-send-whitespace-lines t))
+        (should (funcall check ""))
+        (should-not (funcall check "\na"))
+        (should-not (funcall check "/msg a\n")) ; real /cmd
+        (should-not (funcall check "a\n\nb")) ; "" allowed
+        (should-not (funcall check "/msg a\n\nb")) ; non-/cmd
+        (should-not (funcall check " "))
+        (should-not (funcall check "\t"))
+        (should-not (funcall check "a\nb"))
+        (should-not (funcall check "a\n "))
+        (should-not (funcall check "a\n \t"))
+        (should-not (funcall check "a\n \f"))
+        (should-not (funcall check "a\n \nb"))
+        (should-not (funcall check "a\n \t\nb"))
+        (should-not (funcall check "a\n \f\nb"))))
+
+    (should (funcall check ""))
+    (should (funcall check " "))
+    (should (funcall check "\t"))
+    (should (funcall check "a\n\nb"))
+    (should (funcall check "a\n\nb"))
+    (should (funcall check "a\n "))
+    (should (funcall check "a\n \t"))
+    (should (funcall check "a\n \f"))
+    (should (funcall check "a\n \nb"))
+    (should (funcall check "a\n \t\nb"))
+
+    (should-not (funcall check "a\rb"))
+    (should-not (funcall check "a\nb"))
+    (should-not (funcall check "a\r\nb"))))
 
 (defun erc-tests--with-process-input-spy (test)
   (with-current-buffer (get-buffer-create "FakeNet")
@@ -376,7 +381,7 @@ erc-tests--with-process-input-spy
         (funcall test (lambda () (pop calls)))))
     (when noninteractive (kill-buffer))))
 
-(ert-deftest erc-check-prompt-input-functions ()
+(ert-deftest erc--check-prompt-input-functions ()
   (erc-tests--with-process-input-spy
    (lambda (next)
 
@@ -493,6 +498,31 @@ erc-send-whitespace-lines
        (should (equal (funcall next) '("there\n" nil t)))
        (should-not (funcall next))))))
 
+(ert-deftest erc--check-prompt-input-for-excess-lines ()
+  (ert-info ("Without `erc-inhibit-multiline-input'")
+    (should-not erc-inhibit-multiline-input)
+    (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b"))))
+
+  (ert-info ("With `erc-inhibit-multiline-input' as t (2)")
+    (let ((erc-inhibit-multiline-input t))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a")))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "")))
+      (should (erc--check-prompt-input-for-excess-lines "" '("a" "b")))))
+
+  (ert-info ("With `erc-inhibit-multiline-input' as 3")
+    (let ((erc-inhibit-multiline-input 3))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b")))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b" "")))
+      (should (erc--check-prompt-input-for-excess-lines "" '("a" "b" "c")))))
+
+  (ert-info ("With `erc-ask-about-multiline-input'")
+    (let ((erc-inhibit-multiline-input t)
+          (erc-ask-about-multiline-input t))
+      (ert-simulate-keys '(?n ?\r ?y ?\r)
+        (should (erc--check-prompt-input-for-excess-lines "" '("a" "b")))
+        (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b")))))
+    (should-not erc-ask-about-multiline-input)))
+
 ;; The point of this test is to ensure output is handled identically
 ;; regardless of whether a command handler is summoned.
 
-- 
2.35.1

From bdfb502f7f0e6b1fbc0ea8cfb0336757bf813ab5 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email protected]>
Date: Mon, 21 Mar 2022 19:21:57 -0700
Subject: [PATCH 1/4] Fix regression in erc-send-input-line

* lisp/erc/erc.el (erc-send-input-line): Restore remedial single-space
padding to ensure empty messages typed at the prompt without an
explicit /msg aren't rejected by the server.  This behavior is only
noticeable when `erc-send-whitespace-lines' is active.

* test/lisp/erc/erc-tests.el (erc-process-input-line): Add trailing
newline to more correctly simulate how it's actually called by
`erc-send-input'. (Bug#50008)
---
 lisp/erc/erc.el            |  2 ++
 test/lisp/erc/erc-tests.el | 10 +++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 06381c5ebe..29a465a759 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -2817,6 +2817,8 @@ erc-send-input-line-function
 
 (defun erc-send-input-line (target line &optional force)
   "Send LINE to TARGET."
+  (when (string= line "\n")
+    (setq line " \n"))
   (erc-message "PRIVMSG" (concat target " " line) force))
 
 (defun erc-get-arglist (fun)
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 520f10dd4e..10e3c16dfc 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -340,19 +340,19 @@ erc-process-input-line
         (ert-info ("Implicit cmd via `erc-send-input-line-function'")
 
           (ert-info ("Baseline")
-            (erc-process-input-line "hi")
+            (erc-process-input-line "hi\n")
             (should (equal (pop erc-server-flood-queue)
                            '("PRIVMSG #chan :hi\r\n" . utf-8))))
 
           (ert-info ("Spaces preserved")
-            (erc-process-input-line "hi you")
+            (erc-process-input-line "hi you\n")
             (should (equal (pop erc-server-flood-queue)
                            '("PRIVMSG #chan :hi you\r\n" . utf-8))))
 
-          (ert-info ("Empty line transmitted without injected-space kludge")
-            (erc-process-input-line "")
+          (ert-info ("Empty line transmitted with injected-space kludge")
+            (erc-process-input-line "\n")
             (should (equal (pop erc-server-flood-queue)
-                           '("PRIVMSG #chan :\r\n" . utf-8))))
+                           '("PRIVMSG #chan : \r\n" . utf-8))))
 
           (should-not calls))))))
 
-- 
2.35.1

From 97f18350d52791c57e325e828997e4440119b7ff Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email protected]>
Date: Tue, 5 Apr 2022 17:45:00 -0700
Subject: [PATCH 2/4] Add some ERC test helpers

* test/lisp/erc/erc-tests.el (erc-tests--test-prep,
erc-tests--set-fake-server-process): Factor out some common
buffer-prep boilerplate involving user input and the server process.
Shared with bug#54536.
---
 test/lisp/erc/erc-tests.el | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 10e3c16dfc..c9254e6d42 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -114,6 +114,20 @@ erc-with-all-buffers-of-server
     (should (get-buffer "#spam"))
     (kill-buffer "#spam")))
 
+(defun erc-tests--send-prep ()
+  (erc-mode)
+  (insert "\n\n")
+  (setq erc-input-marker (make-marker)
+        erc-insert-marker (make-marker))
+  (set-marker erc-insert-marker (point-max))
+  (erc-display-prompt)
+  (should (= (point) erc-input-marker)))
+
+(defun erc-tests--set-fake-server-process (&rest args)
+  (setq erc-server-process
+        (apply #'start-process (car args) (current-buffer) args))
+  (set-process-query-on-exit-flag erc-server-process nil))
+
 (ert-deftest erc--switch-to-buffer ()
   (defvar erc-modified-channels-alist) ; lisp/erc/erc-track.el
 
@@ -197,14 +211,10 @@ erc-ring-previous-command-base-case
 (ert-deftest erc-ring-previous-command ()
   (with-current-buffer (get-buffer-create "*#fake*")
     (erc-mode)
-    (insert "\n\n")
+    (erc-tests--send-prep)
+    (setq-local erc-last-input-time 0)
     (should-not (local-variable-if-set-p 'erc-send-completed-hook))
     (set (make-local-variable 'erc-send-completed-hook) nil) ; skip t (globals)
-    (setq erc-input-marker (make-marker)
-          erc-insert-marker (make-marker))
-    (set-marker erc-insert-marker (point-max))
-    (erc-display-prompt)
-    (should (= (point) erc-input-marker))
     ;; Just in case erc-ring-mode is already on
     (setq-local erc-pre-send-functions nil)
     (add-hook 'erc-pre-send-functions #'erc-add-to-input-ring)
-- 
2.35.1

From 0898d4eb0b37e3faae8cd8c37c756a2cfde1873d Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email protected]>
Date: Mon, 21 Mar 2022 05:40:16 -0700
Subject: [PATCH 3/4] Improve ERC's handling of multiline prompt input

* lisp/erc/erc.el (erc--pre-send-split-functions): Add new internal
hook allowing members to revise individual lines before sending.  This
was created with an eye toward possibly exporting it publicly as a
customizable option.
(erc-last-input-time): Tweak meaning of variable to match likely
original intent, which is that it's only updated on successful calls
to `erc-send-current-line'.
(erc--discard-trailing-multiline-nulls): Conditionally truncate list
of lines to be sent, skipping trailing blanks.  This constitutes a
behavioral change, but considering the nature of the bug being fixed,
is thought to be justified.
(erc--input-split): Add new internal struct containing split input
lines and flag for command detection.
(erc--input-line-delim-regexp): Add regex var for splitting multiline
prompt input.
(erc--blank-in-multiline-p): Add helper for detecting blank lines.
(erc--check-prompt-input-for-multiline-blanks,
erc--check-prompt-input-for-point-in-bounds,
erc--check-prompt-input-for-running-process): New functions to
encapsulate logic for various pre-flight idiot checks.
(erc--check-prompt-input-functions): Add new hook for validating
prompt input prior to clearing it.  Keep it internal for now.
(erc-send-current-line): pre-screen for blank lines and bail out if
necessary.
(erc-send-input): Add optional param to skip checking for blank lines.
Call hook `erc--pre-send-split-functions'.

* test/lisp/erc/erc-tests.el (erc-ring-previous-command): Use new test
helper.
(erc--input-line-delim-regexp,
erc--blank-in-multiline-input-p): Add tests.
(erc-tests--send-prep, erc-tests--set-fake-server-process,
erc-tests--with-process-input-spy): Add test helpers.
(erc--check-prompt-input-functions, erc-send-current-line,
erc-send-whitespace-lines): Add tests.
(Bug#54536)
---
 lisp/erc/erc.el            | 161 +++++++++++++++++++++--------
 test/lisp/erc/erc-tests.el | 202 +++++++++++++++++++++++++++++++++++++
 2 files changed, 322 insertions(+), 41 deletions(-)

diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 29a465a759..d4ca8665a4 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -1054,6 +1054,28 @@ erc-pre-send-functions
   :type 'hook
   :version "27.1")
 
+;; This is being auditioned for possible exporting (as a custom
+;; option).  Likewise for (public versions of) `erc--input-split' and
+;; `erc--discard-trailing-multiline-nulls'.  If unneeded, we'll just
+;; run the latter on the input after `erc-pre-send-functions', and
+;; remove this hook and the struct completely.
+
+(defvar erc--pre-send-split-functions '(erc--discard-trailing-multiline-nulls)
+  "Special hook for modifying individual lines in multiline prompt input.
+The functions are called with one argument, an `erc--input-split'
+struct, which they can optionally modify.
+
+The struct has five slots:
+
+  `string': The input string delivered by `erc-pre-send-functions'.
+  `insertp': Whether the lines should be inserted into the ERC buffer.
+  `sendp': Whether the lines should be sent to the IRC server.
+  `lines': A list of lines to be sent, each one a `string'.
+  `cmdp': Whether to interpret the input as a command, like /ignore.
+
+The `string' field is effectively read-only.  When `cmdp' is non-nil,
+all but the first line will be discarded.")
+
 (defvar erc-insert-this t
   "Insert the text into the target buffer or not.
 Functions on `erc-insert-pre-hook' can set this variable to nil
@@ -5536,7 +5558,7 @@ erc-end-of-input-line
   (point-max))
 
 (defvar erc-last-input-time 0
-  "Time of last call to `erc-send-current-line'.
+  "Time of last successful call to `erc-send-current-line'.
 If that function has never been called, the value is 0.")
 
 (defcustom erc-accidental-paste-threshold-seconds 0.2
@@ -5552,6 +5574,62 @@ erc-accidental-paste-threshold-seconds
   :version "26.1"
   :type '(choice number (other :tag "disabled" nil)))
 
+(defvar erc--input-line-delim-regexp (rx (| (: (? ?\r) ?\n) ?\r)))
+
+(defun erc--blank-in-multiline-input-p (lines)
+  "Detect whether LINES contains a blank line.
+When `erc-send-whitespace-lines' is in effect, return nil if LINES is
+multiline or the first non-empty.  When `erc-send-whitespace-lines' is
+nil, return non-nil when any line is empty or consists of one or more
+spaces, tabs, or form-feeds."
+  (catch 'return
+    (let ((multilinep (cdr lines)))
+      (dolist (line lines)
+        (when (if erc-send-whitespace-lines
+                  (and (string-empty-p line) (not multilinep))
+                (string-match (rx bot (* (in " \t\f")) eot) line))
+          (throw 'return t))))))
+
+(defun erc--discard-trailing-multiline-nulls (state)
+  "Ensure last line of `erc-input' STATE's string is non-null.
+But only when `erc-send-whitespace-lines' is non-nil."
+  (when erc-send-whitespace-lines
+    (when (string-match "[\r\n]+\\'" (erc-input-string state))
+      (setf (erc--input-split-lines state)
+            (split-string (substring (erc-input-string state)
+                                     0
+                                     (match-beginning 0))
+                          erc--input-line-delim-regexp)
+            (erc--input-split-cmdp state) nil))))
+
+(defun erc--check-prompt-input-for-multiline-blanks (_ lines)
+  "Return non-nil when multiline prompt input has blank LINES."
+  (when (erc--blank-in-multiline-input-p lines)
+    (if erc-warn-about-blank-lines
+        "Blank line - ignoring..."
+      'invalid)))
+
+(defun erc--check-prompt-input-for-point-in-bounds (_ _)
+  "Return non-nil when point is before prompt."
+  (when (< (point) (erc-beg-of-input-line))
+    "Point is not in the input area"))
+
+(defun erc--check-prompt-input-for-running-process (string _)
+  "Return non-nil unless in an active ERC server buffer."
+  (unless (or (erc-server-buffer-live-p)
+              (erc-command-no-process-p string))
+    "ERC: No process running"))
+
+(defvar erc--check-prompt-input-functions
+  '(erc--check-prompt-input-for-point-in-bounds
+    erc--check-prompt-input-for-multiline-blanks
+    erc--check-prompt-input-for-running-process)
+  "Validators for user input typed at prompt.
+Called with latest input string submitted by user and the list of lines
+produced by splitting it.  If any member function returns non-nil,
+processing is abandoned and input is left untouched.  When the returned
+value is a string, pass it to `erc-error'.")
+
 (defun erc-send-current-line ()
   "Parse current line and send it to IRC."
   (interactive)
@@ -5565,20 +5643,21 @@ erc-send-current-line
                      (eolp))
             (expand-abbrev))
           (widen)
-          (if (< (point) (erc-beg-of-input-line))
-              (erc-error "Point is not in the input area")
+          (if-let* ((str (erc-user-input))
+                    (msg (run-hook-with-args-until-success
+                          'erc--check-prompt-input-functions str
+                          (split-string str erc--input-line-delim-regexp))))
+              (when (stringp msg)
+                (erc-error msg))
             (let ((inhibit-read-only t)
-                  (str (erc-user-input))
                   (old-buf (current-buffer)))
-              (if (and (not (erc-server-buffer-live-p))
-                       (not (erc-command-no-process-p str)))
-                  (erc-error "ERC: No process running")
+              (progn ; unprogn this during next major surgery
                 (erc-set-active-buffer (current-buffer))
                 ;; Kill the input and the prompt
                 (delete-region (erc-beg-of-input-line)
                                (erc-end-of-input-line))
                 (unwind-protect
-                    (erc-send-input str)
+                    (erc-send-input str 'skip-ws-chk)
                   ;; Fix the buffer if the command didn't kill it
                   (when (buffer-live-p old-buf)
                     (with-current-buffer old-buf
@@ -5593,8 +5672,8 @@ erc-send-current-line
                           (set-buffer-modified-p buffer-modified))))))
 
                 ;; Only when last hook has been run...
-                (run-hook-with-args 'erc-send-completed-hook str))))
-          (setq erc-last-input-time now))
+                (run-hook-with-args 'erc-send-completed-hook str)))
+            (setq erc-last-input-time now)))
       (switch-to-buffer "*ERC Accidental Paste Overflow*")
       (lwarn 'erc :warning
              "You seem to have accidentally pasted some text!"))))
@@ -5611,21 +5690,20 @@ erc-command-regexp
 (cl-defstruct erc-input
   string insertp sendp)
 
-(defun erc-send-input (input)
+(cl-defstruct (erc--input-split (:include erc-input))
+  lines cmdp)
+
+(defun erc-send-input (input &optional skip-ws-chk)
   "Treat INPUT as typed in by the user.
 It is assumed that the input and the prompt is already deleted.
 Return non-nil only if we actually send anything."
   ;; Handle different kinds of inputs
-  (cond
-   ;; Ignore empty input
-   ((if erc-send-whitespace-lines
-        (string= input "")
-      (string-match "\\`[ \t\r\f\n]*\\'" input))
-    (when erc-warn-about-blank-lines
-      (message "Blank line - ignoring...")
-      (beep))
-    nil)
-   (t
+  (if (and (not skip-ws-chk)
+           (erc--check-prompt-input-for-multiline-blanks
+            input (split-string input erc--input-line-delim-regexp)))
+      (when erc-warn-about-blank-lines
+        (message "Blank line - ignoring...") ; compat
+        (beep))
     ;; This dynamic variable is used by `erc-send-pre-hook'.  It's
     ;; obsolete, and when it's finally removed, this binding should
     ;; also be removed.
@@ -5645,27 +5723,28 @@ erc-send-input
 				  :insertp erc-insert-this
 				  :sendp erc-send-this))
       (run-hook-with-args 'erc-pre-send-functions state)
+      (setq state (make-erc--input-split
+                   :string (erc-input-string state)
+                   :insertp (erc-input-insertp state)
+                   :sendp (erc-input-sendp state)
+                   :lines (split-string (erc-input-string state)
+                                        erc--input-line-delim-regexp)
+                   :cmdp (string-match erc-command-regexp
+                                       (erc-input-string state))))
+      (run-hook-with-args 'erc--pre-send-split-functions state)
       (when (and (erc-input-sendp state)
-		 erc-send-this)
-	(let ((string (erc-input-string state)))
-          (if (or (if (>= emacs-major-version 28)
-                      (string-search "\n" string)
-                    (string-match "\n" string))
-                  (not (string-match erc-command-regexp string)))
-              (mapc
-               (lambda (line)
-		 (mapc
-                  (lambda (line)
-                    ;; Insert what has to be inserted for this.
-		    (when (erc-input-insertp state)
-                      (erc-display-msg line))
-                    (erc-process-input-line (concat line "\n")
-                                            (null erc-flood-protect) t))
-                  (or (and erc-flood-protect (erc-split-line line))
-                      (list line))))
-               (split-string string "\n"))
-            (erc-process-input-line (concat string "\n") t nil))
-          t))))))
+                 erc-send-this)
+        (let ((lines (erc--input-split-lines state)))
+          (if (and (erc--input-split-cmdp state) (not (cdr lines)))
+              (erc-process-input-line (concat (car lines) "\n") t nil)
+            (dolist (line lines)
+              (dolist (line (or (and erc-flood-protect (erc-split-line line))
+                                (list line)))
+                (when (erc-input-insertp state)
+                  (erc-display-msg line))
+                (erc-process-input-line (concat line "\n")
+                                        (null erc-flood-protect) t))))
+          t)))))
 
 ;; (defun erc-display-command (line)
 ;;   (when erc-insert-this
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index c9254e6d42..c076503933 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -295,6 +295,208 @@ erc-log-irc-protocol
     (kill-buffer "*erc-protocol*")
     (should-not erc-debug-irc-protocol)))
 
+(ert-deftest erc--input-line-delim-regexp ()
+  (let ((p erc--input-line-delim-regexp))
+    ;; none
+    (should (equal '("a" "b") (split-string "a\r\nb" p)))
+    (should (equal '("a" "b") (split-string "a\nb" p)))
+    (should (equal '("a" "b") (split-string "a\rb" p)))
+
+    ;; one
+    (should (equal '("") (split-string "" p)))
+    (should (equal '("a" "" "b") (split-string "a\r\rb" p)))
+    (should (equal '("a" "" "b") (split-string "a\n\rb" p)))
+    (should (equal '("a" "" "b") (split-string "a\n\nb" p)))
+    (should (equal '("a" "" "b") (split-string "a\r\r\nb" p)))
+    (should (equal '("a" "" "b") (split-string "a\n\r\nb" p)))
+    (should (equal '("a" "") (split-string "a\n" p)))
+    (should (equal '("a" "") (split-string "a\r" p)))
+    (should (equal '("a" "") (split-string "a\r\n" p)))
+    (should (equal '("" "b") (split-string "\nb" p)))
+    (should (equal '("" "b") (split-string "\rb" p)))
+    (should (equal '("" "b") (split-string "\r\nb" p)))
+
+    ;; two
+    (should (equal '("" "") (split-string "\r" p)))
+    (should (equal '("" "") (split-string "\n" p)))
+    (should (equal '("" "") (split-string "\r\n" p)))
+
+    ;; three
+    (should (equal '("" "" "") (split-string "\r\r" p)))
+    (should (equal '("" "" "") (split-string "\n\n" p)))
+    (should (equal '("" "" "") (split-string "\n\r" p)))))
+
+(ert-deftest erc--blank-in-multiline-input-p ()
+  (let ((check (lambda (s)
+                 (erc--blank-in-multiline-input-p
+                  (split-string s erc--input-line-delim-regexp)))))
+
+    (ert-info ("With `erc-send-whitespace-lines'")
+      (let ((erc-send-whitespace-lines t))
+        (should (funcall check ""))
+        (should-not (funcall check "\na"))
+        (should-not (funcall check "/msg a\n")) ; real /cmd
+        (should-not (funcall check "a\n\nb")) ; "" allowed
+        (should-not (funcall check "/msg a\n\nb")) ; non-/cmd
+        (should-not (funcall check " "))
+        (should-not (funcall check "\t"))
+        (should-not (funcall check "a\nb"))
+        (should-not (funcall check "a\n "))
+        (should-not (funcall check "a\n \t"))
+        (should-not (funcall check "a\n \f"))
+        (should-not (funcall check "a\n \nb"))
+        (should-not (funcall check "a\n \t\nb"))
+        (should-not (funcall check "a\n \f\nb"))))
+
+    (should (funcall check ""))
+    (should (funcall check " "))
+    (should (funcall check "\t"))
+    (should (funcall check "a\n\nb"))
+    (should (funcall check "a\n\nb"))
+    (should (funcall check "a\n "))
+    (should (funcall check "a\n \t"))
+    (should (funcall check "a\n \f"))
+    (should (funcall check "a\n \nb"))
+    (should (funcall check "a\n \t\nb"))
+
+    (should-not (funcall check "a\rb"))
+    (should-not (funcall check "a\nb"))
+    (should-not (funcall check "a\r\nb"))))
+
+(defun erc-tests--with-process-input-spy (test)
+  (with-current-buffer (get-buffer-create "FakeNet")
+    (let* ((erc-pre-send-functions
+            (remove #'erc-add-to-input-ring erc-pre-send-functions)) ; for now
+           (inhibit-message noninteractive)
+           (erc-server-current-nick "tester")
+           (erc-last-input-time 0)
+           erc-accidental-paste-threshold-seconds
+           ;;
+           calls)
+      (cl-letf (((symbol-function 'erc-process-input-line)
+                 (lambda (&rest r) (push r calls)))
+                ((symbol-function 'erc-server-buffer)
+                 (lambda () (current-buffer))))
+        (erc-tests--send-prep)
+        (funcall test (lambda () (pop calls)))))
+    (when noninteractive (kill-buffer))))
+
+(ert-deftest erc--check-prompt-input-functions ()
+  (erc-tests--with-process-input-spy
+   (lambda (next)
+
+     (ert-info ("Errors when point not in prompt area") ; actually just dings
+       (insert "/msg #chan hi")
+       (forward-line -1)
+       (let ((e (should-error (erc-send-current-line))))
+         (should (equal "Point is not in the input area" (cadr e))))
+       (goto-char (point-max))
+       (ert-info ("Input remains untouched")
+         (should (save-excursion (erc-bol) (looking-at "/msg #chan hi")))))
+
+     (ert-info ("Errors when no process running")
+       (let ((e (should-error (erc-send-current-line))))
+         (should (equal "ERC: No process running" (cadr e))))
+       (ert-info ("Input remains untouched")
+         (should (save-excursion (erc-bol) (looking-at "/msg #chan hi")))))
+
+     (ert-info ("Errors when line contains empty newline")
+       (erc-bol)
+       (delete-region (point) (point-max))
+       (insert "one\n")
+       (let ((e (should-error (erc-send-current-line))))
+         (should (equal "Blank line - ignoring..." (cadr e))))
+       (goto-char (point-max))
+       (ert-info ("Input remains untouched")
+         (should (save-excursion (goto-char erc-input-marker)
+                                 (looking-at "one\n")))))
+
+     (should (= 0 erc-last-input-time))
+     (should-not (funcall next)))))
+
+;; These also indirectly tests `erc-send-input'
+
+(ert-deftest erc-send-current-line ()
+  (erc-tests--with-process-input-spy
+   (lambda (next)
+     (erc-tests--set-fake-server-process "sleep" "1")
+     (should (= 0 erc-last-input-time))
+
+     (ert-info ("Simple command")
+       (insert "/msg #chan hi")
+       (erc-send-current-line)
+       (ert-info ("Prompt restored")
+         (forward-line 0)
+         (should (looking-at-p erc-prompt)))
+       (ert-info ("Input cleared")
+         (erc-bol)
+         (should (eq (point) (point-max))))
+       ;; Commands are forced (no flood protection)
+       (should (equal (funcall next) '("/msg #chan hi\n" t nil))))
+
+     (ert-info ("Simple non-command")
+       (insert "hi")
+       (erc-send-current-line)
+       (should (eq (point) (point-max)))
+       (should (save-excursion (forward-line -1)
+                               (search-forward "<tester> hi")))
+       ;; Non-ommands are forced only when `erc-flood-protect' is nil
+       (should (equal (funcall next) '("hi\n" nil t))))
+
+     (should (consp erc-last-input-time)))))
+
+(ert-deftest erc-send-whitespace-lines ()
+  (erc-tests--with-process-input-spy
+   (lambda (next)
+     (erc-tests--set-fake-server-process "sleep" "1")
+     (setq-local erc-send-whitespace-lines t)
+
+     (ert-info ("Multiline hunk with blank line correctly split")
+       (insert "one\n\ntwo")
+       (erc-send-current-line)
+       (ert-info ("Prompt restored")
+         (forward-line 0)
+         (should (looking-at-p erc-prompt)))
+       (ert-info ("Input cleared")
+         (erc-bol)
+         (should (eq (point) (point-max))))
+       (should (equal (funcall next) '("two\n" nil t)))
+       (should (equal (funcall next) '("\n" nil t)))
+       (should (equal (funcall next) '("one\n" nil t))))
+
+     (ert-info ("Multiline hunk with trailing newline filtered")
+       (insert "hi\n")
+       (erc-send-current-line)
+       (ert-info ("Input cleared")
+         (erc-bol)
+         (should (eq (point) (point-max))))
+       (should (equal (funcall next) '("hi\n" nil t)))
+       (should-not (funcall next)))
+
+     (ert-info ("Multiline hunk with trailing carriage filtered")
+       (insert "hi\r")
+       (erc-send-current-line)
+       (ert-info ("Input cleared")
+         (erc-bol)
+         (should (eq (point) (point-max))))
+       (should (equal (funcall next) '("hi\n" nil t)))
+       (should-not (funcall next)))
+
+     (ert-info ("Multiline command with trailing blank filtered")
+       (insert "/msg #chan hi\r")
+       (erc-send-current-line)
+       (ert-info ("Input cleared")
+         (erc-bol)
+         (should (eq (point) (point-max))))
+       (should (equal (funcall next) '("/msg #chan hi\n" nil t)))
+       (should-not (funcall next)))
+
+     (ert-info ("Multiline hunk with trailing whitespace not filtered")
+       (insert "there\n ")
+       (erc-send-current-line)
+       (should (equal (funcall next) '(" \n" nil t)))
+       (should (equal (funcall next) '("there\n" nil t)))
+       (should-not (funcall next))))))
 
 ;; The point of this test is to ensure output is handled identically
 ;; regardless of whether a command handler is summoned.
-- 
2.35.1

From cb445bf2b95737df7fdcb47be3e9937c983cd705 Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email protected]>
Date: Wed, 27 Apr 2022 02:27:32 -0700
Subject: [PATCH 4/4] Optionally prevent sending multiline input in ERC

* lisp/erc/erc.el (erc-inhibit-multiline-input): Add option to cap the
number of lines to be sent before admonishing the user.
(erc-ask-about-multiline-input): Add option to ask instead of warning
user when `erc-inhibit-multiline-input' is reached.
(erc--check-prompt-input-for-excess-lines): Add validator to check
to possibly warn when too many lines are submitted for transmission.

* test/lisp/erc/erc-tests.el
(erc--check-prompt-input-for-excess-lines): Add test.
(Bug#54536)
---
 lisp/erc/erc.el            | 34 +++++++++++++++++++++++++++++++++-
 test/lisp/erc/erc-tests.el | 25 +++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index d4ca8665a4..8e96dd30c4 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -224,6 +224,20 @@ erc-send-whitespace-lines
   :group 'erc
   :type 'boolean)
 
+(defcustom erc-inhibit-multiline-input nil
+  "Conditionally disallow input consisting of multiple lines.
+Issue an error when the number of input lines submitted for sending
+exceeds this value."
+  :package-version '(ERC . "5.4.1") ; FIXME match to next release
+  :group 'erc
+  :type '(choice integer boolean))
+
+(defcustom erc-ask-about-multiline-input nil
+  "Ask to ignore `erc-inhibit-multiline-input' when tripped."
+  :package-version '(ERC . "5.4.1") ; FIXME match to next release
+  :group 'erc
+  :type 'boolean)
+
 (defcustom erc-hide-prompt nil
   "If non-nil, do not display the prompt for commands.
 
@@ -5602,6 +5616,23 @@ erc--discard-trailing-multiline-nulls
                           erc--input-line-delim-regexp)
             (erc--input-split-cmdp state) nil))))
 
+(defun erc--check-prompt-input-for-excess-lines (_ lines)
+  "Return non-nil when trying to send too many LINES."
+  (when erc-inhibit-multiline-input
+    ;; Assume `erc--discard-trailing-multiline-nulls' is set to run
+    (let ((reversed (seq-drop-while #'string-empty-p (reverse lines)))
+          (max (if (eq erc-inhibit-multiline-input t)
+                   2
+                 erc-inhibit-multiline-input))
+          (seen 0)
+          msg)
+      (while (and (pop reversed) (< (cl-incf seen) max)))
+      (when (= seen max)
+        (setq msg (format "(exceeded by %d)" (1+ (length reversed))))
+        (unless (and erc-ask-about-multiline-input
+                     (y-or-n-p (concat "Send input " msg "?")))
+          (concat "Too many lines " msg))))))
+
 (defun erc--check-prompt-input-for-multiline-blanks (_ lines)
   "Return non-nil when multiline prompt input has blank LINES."
   (when (erc--blank-in-multiline-input-p lines)
@@ -5623,7 +5654,8 @@ erc--check-prompt-input-for-running-process
 (defvar erc--check-prompt-input-functions
   '(erc--check-prompt-input-for-point-in-bounds
     erc--check-prompt-input-for-multiline-blanks
-    erc--check-prompt-input-for-running-process)
+    erc--check-prompt-input-for-running-process
+    erc--check-prompt-input-for-excess-lines)
   "Validators for user input typed at prompt.
 Called with latest input string submitted by user and the list of lines
 produced by splitting it.  If any member function returns non-nil,
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index c076503933..fa39f4fcc6 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -498,6 +498,31 @@ erc-send-whitespace-lines
        (should (equal (funcall next) '("there\n" nil t)))
        (should-not (funcall next))))))
 
+(ert-deftest erc--check-prompt-input-for-excess-lines ()
+  (ert-info ("Without `erc-inhibit-multiline-input'")
+    (should-not erc-inhibit-multiline-input)
+    (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b"))))
+
+  (ert-info ("With `erc-inhibit-multiline-input' as t (2)")
+    (let ((erc-inhibit-multiline-input t))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a")))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "")))
+      (should (erc--check-prompt-input-for-excess-lines "" '("a" "b")))))
+
+  (ert-info ("With `erc-inhibit-multiline-input' as 3")
+    (let ((erc-inhibit-multiline-input 3))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b")))
+      (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b" "")))
+      (should (erc--check-prompt-input-for-excess-lines "" '("a" "b" "c")))))
+
+  (ert-info ("With `erc-ask-about-multiline-input'")
+    (let ((erc-inhibit-multiline-input t)
+          (erc-ask-about-multiline-input t))
+      (ert-simulate-keys '(?n ?\r ?y ?\r)
+        (should (erc--check-prompt-input-for-excess-lines "" '("a" "b")))
+        (should-not (erc--check-prompt-input-for-excess-lines "" '("a" "b")))))
+    (should-not erc-ask-about-multiline-input)))
+
 ;; The point of this test is to ensure output is handled identically
 ;; regardless of whether a command handler is summoned.
 
-- 
2.35.1