magit-git-wash: Always keep error output

Remove the variable `magit--git-wash-keep-error' which previously could
be used to disable that.  The variable was added in [1: 78a979fde5] and
its value was changed to t in [2: 76253bda0d].  This has generally held
up well enough to be permanently enabled.

Function `magit--git-wash', which was added in [1: 78a979fde5], can be
used in cases where the section should be canceled in case of an error.

Also extend the docstrings of these two functions.

1: 2023-03-18 78a979fde52815242b165f083d171259db28e0b4
   Support displaying errors that occur when washing a section

2: 2024-11-15 76253bda0d05d252e118e56955447b6e4d6c0535
   magit--git-wash-keep-error: Enable by default

2 files changed, 17 insertions, 9 deletions

diff --git a/lisp/magit-diff.el b/lisp/magit-diff.el
index eb904fa..7e87fa5 100644
--- a/lisp/magit-diff.el
+++ b/lisp/magit-diff.el
@@ -2240,7 +2240,7 @@ keymap is the parent of their keymaps."
     (magit--git-wash #'magit-diff-wash-diffs
         (if (member "--no-index" args)
             'wash-anyway
-          (or keep-error magit--git-wash-keep-error))
+          (or keep-error t))
       cmd args)))
 
 (defun magit-diff--maybe-add-stat-arguments (args)
diff --git a/lisp/magit-git.el b/lisp/magit-git.el
index 41587bc..d432531 100644
--- a/lisp/magit-git.el
+++ b/lisp/magit-git.el
@@ -543,18 +543,26 @@ a section in the respective process buffer."
     (apply #'magit-git-insert args)
     (split-string (buffer-string) "\0" t)))
 
-(defvar magit--git-wash-keep-error t)
-
 (defun magit-git-wash (washer &rest args)
-  "Execute Git with ARGS, inserting washed output at point.
-Actually first insert the raw output at point.  If there is no
-output, call `magit-cancel-section'.  Otherwise temporarily narrow
-the buffer to the inserted text, move to its beginning, and then
-call function WASHER with ARGS as its sole argument."
+  "Execute git with ARGS, inserting washed output at point.
+
+First insert the raw output at point.  If there is no output, call
+`magit-cancel-section'.  Otherwise temporarily narrow the buffer to
+the inserted text, move to its beginning, and finally call function
+WASHER with ARGS as its sole argument.
+
+If git exits with a non-zero exit status, apply the `error' face to
+the error message, instead of calling WASHER.  To instead cancel the
+section use `magit--git-wash'."
   (declare (indent 1))
-  (apply #'magit--git-wash washer magit--git-wash-keep-error args))
+  (apply #'magit--git-wash washer t args))
 
 (defun magit--git-wash (washer keep-error &rest args)
+  "Execute git with ARGS, inserting washed output at point.
+
+Like `magit-git-wash' but if KEEP-ERROR is nil and an error occurs, also
+insert standard error.  If KEEP-ERROR is `wash-anyway', insert and wash
+standard output even in case of an error."
   (declare (indent 2))
   (setq args (flatten-tree args))
   (let ((beg (point))