Optional space and unit in `file-size-human-readable' (bug#35756)

To improve readability of strings produced by
`file-size-human-readable', add two optional arguments:

- SPACE, to provide a string (typically a space or non-breaking space)
to put between the number and unit.  For compatibility, the default is
an empty string.

- UNIT, a string to use as unit.  For compatibility, the default is
"B" in `iec' mode and the empty string otherwise.

Also fix a glitch with small numbers in `iec' mode which caused a
stray "i" in the result.

* lisp/files.el (file-size-human-readable):
Add optional SPACE and UNIT arguments and handle small numbers correctly.
(files--ask-user-about-large-file, warn-maybe-out-of-memory):
Call with `iec' and space.
* test/lisp/files-tests.el (files-test-file-size-human-readable): New test.
* lisp/url/url-http.el (url-http-simple-after-change-function)
(url-http-content-length-after-change-function): Call with `iec' and space.
* etc/NEWS (Lisp Changes): Mention the change.

1 files changed, 9 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 02b42921ab1..dca7a72b812 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2163,6 +2163,15 @@ The functions 'base64-decode-string' and 'base64-decode-region' now
 accept an optional argument to decode the URL variant of base-64
 encoding.
 
++++
+** The function 'file-size-human-readable' accepts more optional arguments.
+The new third argument is a string put between the number and unit; it
+defaults to the empty string.  The new fourth argument is a string
+representing the unit to use; it defaults to "B" when the second
+argument is 'iec' and the empty string otherwise.  We recomment a
+space or non-breaking space as third argument, and "B" as fourth
+argument, circumstances allowing.
+
 
 * Changes in Emacs 27.1 on Non-Free Operating Systems