Some file names are no longer sanitized

[Chaton666]

When uploading a file which filename contain accents, those accents are no longer replaced by non-accent letter.
It's specific to JPEG file.
Tested with PDF and PNG: accent are well removed.

See attached screenshot with JPEG, PNG and PDF example.

I can reproduce this with WP 5.9 RC2 and WP 5.8.3.

[audrasjb]

Thanks for opening this issue @Chaton666, let's move this to milestone 5.9 for further investigation.

[Chaton666]

It's look like the problem is in the sanitize_file_name function (wp-includes/formatting.php).
With a file named "Exemple-1-activités-de-construction.jpg", I don't pass this check and accent is not removed :

// Return if only one extension.
if ( count( $parts ) <= 2 ) {
	/** This filter is documented in wp-includes/formatting.php */
	return apply_filters( 'sanitize_file_name', $filename, $filename_raw );
}

[Chaton666]

Well, it has nothing to do with JPEG file type.
With a file named "Exemple-2-activités-de-construction.png" (PNG), accent is not removed.
I guess there is, in this filename, some pattern which is not processed by str_replace and preg_replace.

[Chaton666]

After some research, my "é" is not a real é.
Found on StackOverflow (​https://stackoverflow.com/a/41991113/5798787) :

"Your character é is actually 0x65cc81, rather than the more usual single Unicode codepoint in UTF-8 0xc3a9 (é LATIN SMALL LETTER E WITH ACUTE (U+00E9)). 0x65cc81 is a Unicode "Combining sequence": 0x65 is e "LATIN SMALL LETTER E" (U+0065) and 0xcc81 is ́ "COMBINING ACUTE ACCENT (U+0301)"."

[Chaton666]

Here is a patch adding "Latin small letter e with combining acute accent" to the characters to filters in remove_accents function.

[audrasjb]

Alright, this is a known issue and it wasn't introduced in 5.9 cycle.
Let's move this back to the awaiting review queue.

Also we need a fix for other combinaisons as well.