branch: externals/compat
commit 10e6509878001c77bb5a00b51b33210c3347db97
Author: Daniel Mendler <m...@daniel-mendler.de>
Commit: Daniel Mendler <m...@daniel-mendler.de>
compat-30: Add require-with-check
---
NEWS.org | 1 +
compat-30.el | 25 +++++++++++++++++++++++++
compat-tests.el | 20 ++++++++++++++++++++
compat.texi | 14 ++++++++++++++
4 files changed, 60 insertions(+)
diff --git a/NEWS.org b/NEWS.org
index 90da0c285d..043d45ac15 100644
--- a/NEWS.org
+++ b/NEWS.org
@@ -10,6 +10,7 @@
- compat-30: New function =merge-ordered-lists=.
- compat-30: New variables =completion-lazy-hilit= and
=completion-lazy-hilit-fn=
and new function =completion-lazy-hilit=.
+- compat-30: New function =require-with-check=.
* Release of "Compat" Version 29.1.4.4
diff --git a/compat-30.el b/compat-30.el
index 90b8a11a44..36e6a19d02 100644
--- a/compat-30.el
+++ b/compat-30.el
@@ -27,6 +27,31 @@
;; TODO Update to 30.1 as soon as the Emacs emacs-30 branch version bumped
(compat-version "30.0.50")
+;;;; Defined in files.el
+
+(compat-defun require-with-check (feature &optional filename noerror) ;;
<compat-tests:require-with-check>
+ "If FEATURE is not already loaded, load it from FILENAME.
+This is like `require' except if FEATURE is already a member of the list
+`features’, then we check if this was provided by a different file than the
+one that we would load now (presumably because `load-path' has been
+changed since the file was loaded).
+If it's the case, we either signal an error (the default), or forcibly reload
+the new file (if NOERROR is equal to `reload'), or otherwise emit a warning."
+ (let ((lh load-history)
+ (res (require feature filename (if (eq noerror 'reload) nil noerror))))
+ ;; If the `feature' was not yet provided, `require' just loaded the right
+ ;; file, so we're done.
+ (when (eq lh load-history)
+ ;; If `require' did nothing, we need to make sure that was warranted.
+ (let ((fn (locate-file (or filename (symbol-name feature))
+ load-path (get-load-suffixes))))
+ (cond
+ ((assoc fn load-history) nil) ;We loaded the right file.
+ ((eq noerror 'reload) (load fn nil 'nomessage))
+ (t (funcall (if noerror #'warn #'error)
+ "Feature provided by other file: %S" feature)))))
+ res))
+
;;;; Defined in minibuffer.el
(compat-defvar completion-lazy-hilit nil ;;
<compat-tests:completion-lazy-hilit>
diff --git a/compat-tests.el b/compat-tests.el
index 2ebd9bfa97..12e52ea370 100644
--- a/compat-tests.el
+++ b/compat-tests.el
@@ -3064,5 +3064,25 @@
'((E C D) (B A) (A C) (D B))
(lambda (_) (error "cycle")))))
+(ert-deftest compat-require-with-check ()
+ ;; TODO enable test on Emacs 30 as soon as the CI supports it.
+ (static-if (< emacs-major-version 30)
+ (ert-with-temp-directory dir1
+ (ert-with-temp-directory dir2
+ (dolist (dir (list dir1 dir2))
+ (with-temp-buffer
+ (insert "(provide 'compat-reload)")
+ (write-region (point-min) (point-max)
+ (file-name-concat dir "compat-reload.el"))))
+ (should-not (require-with-check 'compat-does-not-exist nil 'noerror))
+ (should-not (require-with-check 'compat-does-not-exist
"compat-does-not-exist.el" 'noerror))
+ (let ((load-path (cons dir1 load-path)))
+ (should-equal 'compat-reload (require-with-check 'compat-reload))
+ (should-equal 'compat-reload (require-with-check 'compat-reload)))
+ (let ((load-path (cons dir2 load-path)))
+ (should-error (require-with-check 'compat-reload))
+ (should-equal 'compat-reload (require-with-check 'compat-reload nil
'noerror))
+ (should-equal 'compat-reload (require-with-check 'compat-reload nil
'reload)))))))
+
(provide 'compat-tests)
;;; compat-tests.el ends here
diff --git a/compat.texi b/compat.texi
index 39a9c79557..95c9257b79 100644
--- a/compat.texi
+++ b/compat.texi
@@ -3348,6 +3348,20 @@ older than 30.1. Note that due to upstream changes, it
might happen
that there will be the need for changes, so use these functions with
care.
+@c copied from lispref/loading.texi
+@defun require-with-check feature &optional filename noerror
+This function works like @code{require}, except if @var{feature} is
+already loaded (i.e.@: is already a member of the list in
+@code{features}, see below). If @var{feature} is already loaded, this
+function checks if @var{feature} was provided by a file different from
+@var{filename}, and if so, it by default signals an error. If the
+value of the optional argument @var{noerror} is @code{reload}, the
+function doesn't signal an error, but instead forcibly reloads
+@var{filename}; if @var{noerror} is some other non-@code{nil} value,
+the function emits a warning about @var{feature} being already
+provided by another file.
+@end defun
+
@defun merge-ordered-lists lists &optional error-function
Merge @var{lists} in a consistent order. @var{lists} is a list of
lists of elements. Merge them into a single list containing the same
