From 25370397fb45d16f434e1c80bc5b04e8567c9f69 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
Date: Mon, 16 Oct 2023 15:22:51 -0400
Subject: [PATCH] Support turning warnings into errors

Support turning warnings into errors in a user-configurable way.  This
is especially useful in combination with (setq debug-on-error t) to
drop to the debugger when a warning happens.

* lisp/emacs-lisp/warnings.el (warning-suppress-types): Improve
docstring.
(warning-to-error-types, warning-to-error): Add. (bug#66326)
(display-warning): Check warning-to-error-types.
(warning-suppress-p): Allow () to match any type.
---
 lisp/emacs-lisp/warnings.el | 52 ++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 4 deletions(-)

diff --git a/lisp/emacs-lisp/warnings.el b/lisp/emacs-lisp/warnings.el
index 31b840d6c83..f6d10be8141 100644
--- a/lisp/emacs-lisp/warnings.el
+++ b/lisp/emacs-lisp/warnings.el
@@ -114,11 +114,37 @@ warning-suppress-types
 The element must match an initial segment of the list TYPE.
 Thus, (foo bar) as an element matches (foo bar)
 or (foo bar ANYTHING...) as TYPE.
+An empty list as an element matches any TYPE.
 If TYPE is a symbol FOO, that is equivalent to the list (FOO),
 so only the element (FOO) will match it.
 See also `warning-suppress-log-types'."
   :type '(repeat (repeat symbol))
   :version "22.1")
+
+(defcustom warning-to-error-types nil
+  "List of warning types to signal as an error instead.
+If any element of this list matches the TYPE argument to `display-warning',
+`display-warning' signals an error instead of logging a warning.
+See `warning-suppress-types' for the format of elements in this list.
+A useful value is (()) to convert all warnings into errors.
+See also `warning-signal-errors-during-startup'."
+  :type '(repeat (repeat symbol))
+  :version "30.1")
+
+(defcustom warning-signal-errors-during-startup nil
+  "If non-nil, warnings converted into errors are signaled during startup.
+
+Normally, warnings generated during startup are delayed until
+after startup.  This includes warnings converted into errors by
+`warning-to-error-types': they will be signaled after startup
+completes, outside the context of the code which caused the
+warning.  If you'd prefer that these errors be signaled
+immediately so that the context is present during debugging, set
+this variable to nil."
+  :type '(choice
+          (const :tag "Warnings converted into errors raise after startup" nil)
+          (const :tag "Warnings converted into errors raise immediately" t))
+  :version "30.1")
 
 ;; The autoload cookie is so that programs can bind this variable
 ;; safely, testing the existing value, before they call one of the
@@ -180,10 +206,11 @@ warning-suppress-p
   (let (some-match)
     (dolist (elt suppress-list)
       (if (symbolp type)
-	  ;; If TYPE is a symbol, the ELT must be (TYPE).
-	  (if (and (consp elt)
-		   (eq (car elt) type)
-		   (null (cdr elt)))
+	  ;; If TYPE is a symbol, the ELT must be (TYPE) or ().
+	  (if (or (null elt)
+                  (and (consp elt)
+		       (eq (car elt) type)
+		       (null (cdr elt))))
 	      (setq some-match t))
 	;; If TYPE is a list, ELT must match it or some initial segment of it.
 	(let ((tem1 type)
@@ -230,6 +257,15 @@ warnings-suppress
                               (cons (list type) warning-suppress-types)))
     (_ (message "Exiting"))))
 
+(defun warning-to-error (type message level)
+  (unless level
+    (setq level :warning))
+  (let* ((typename (if (consp type) (car type) type))
+         (level-info (assq level warning-levels)))
+    (error (concat (nth 1 level-info) "%s")
+           (format warning-type-format typename)
+           message)))
+
 ;;;###autoload
 (defun display-warning (type message &optional level buffer-name)
   "Display a warning message, MESSAGE.
@@ -263,6 +299,14 @@ display-warning
 disable automatic display of the warning or disable the warning
 entirely by setting `warning-suppress-types' or
 `warning-suppress-log-types' on their behalf."
+  (when (and (>= (warning-numeric-level (or level :warning))
+	         (warning-numeric-level warning-minimum-log-level))
+	     (not (warning-suppress-p type warning-suppress-log-types))
+             (warning-suppress-p type warning-to-error-types)
+             (or warning-signal-errors-during-startup
+                 after-init-time noninteractive (daemonp))
+             )
+    (warning-to-error type message level))
   (if (not (or after-init-time noninteractive (daemonp)))
       ;; Ensure warnings that happen early in the startup sequence
       ;; are visible when startup completes (bug#20792).
-- 
2.39.3