How to let TYPO3 do the error handling and redirecting for missing files

Question

By default the redirecting for known file storages, like the fileadmin directory is prevented by htaccess:

RewriteRule (?:typo3/|fileadmin/|typo3conf/|typo3temp/|uploads/|favicon\.ico) - [L]

But this also prevents the TYPO3 error handling and redirects module from taking action if a file does not exist.

Our editors have the wish to set up redirects for some deleted files and I wonder if there are any negative effects if I don't exclude fileadmin from the RewriteRule.

Why does this rule even exist by default?

Here is the complete TYPO3 default rewriting, to make the context easier to understand:

<IfModule mod_rewrite.c>

# Enable URL rewriting
RewriteEngine On

# Store the current location in an environment variable CWD to use
# mod_rewrite in .htaccess files without knowing the RewriteBase
RewriteCond $0#%{REQUEST_URI} ([^#]*)#(.*)\1$
RewriteRule ^.*$ - [E=CWD:%2]

# Rules to set ApplicationContext based on hostname
#RewriteCond %{HTTP_HOST} ^dev\.example\.com$
#RewriteRule .? - [E=TYPO3_CONTEXT:Development]
#RewriteCond %{HTTP_HOST} ^staging\.example\.com$
#RewriteRule .? - [E=TYPO3_CONTEXT:Production/Staging]
#RewriteCond %{HTTP_HOST} ^www\.example\.com$
#RewriteRule .? - [E=TYPO3_CONTEXT:Production]

# Rule for versioned static files, configured through:
# - $GLOBALS['TYPO3_CONF_VARS']['BE']['versionNumberInFilename']
# - $GLOBALS['TYPO3_CONF_VARS']['FE']['versionNumberInFilename']
# IMPORTANT: This rule has to be the very first RewriteCond in order to work!
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.+)\.(\d+)\.(php|js|css|png|jpg|gif|gzip)$ %{ENV:CWD}$1.$3 [L]

# Access block for folders
RewriteRule _(?:recycler|temp)_/ - [F]
RewriteRule fileadmin/templates/.*\.(?:txt|ts)$ - [F]
RewriteRule ^(?:vendor|typo3_src|typo3temp/var) - [F]
RewriteRule (?:typo3conf/ext|typo3/sysext|typo3/ext)/[^/]+/(?:Configuration|Resources/Private|Tests?|Documentation|docs?)/ - [F]

# Block access to all hidden files and directories with the exception of
# the visible content from within the `/.well-known/` hidden directory (RFC 5785).
RewriteCond %{REQUEST_URI} "!(^|/)\.well-known/([^./]+./?)+$" [NC]
RewriteCond %{SCRIPT_FILENAME} -d [OR]
RewriteCond %{SCRIPT_FILENAME} -f
RewriteRule (?:^|/)\. - [F]

# Stop rewrite processing, if we are in the typo3/ directory or any other known directory
# NOTE: Add your additional local storages here
RewriteRule ^(?:typo3/|fileadmin/|typo3conf/|typo3temp/|uploads/|favicon\.ico) - [L]

# If the file/symlink/directory does not exist => Redirect to index.php.
# For httpd.conf, you need to prefix each '%{REQUEST_FILENAME}' with '%{DOCUMENT_ROOT}'.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^.*$ %{ENV:CWD}index.php [QSA,L]

</IfModule>

Answer 1

RewriteRule (?:typo3/|fileadmin/|typo3conf/|typo3temp/|uploads/|favicon\.ico) - [L]

But this also prevents the TYPO3 error handling and redirects module from taking action if a file does not exist.
[…]
Why does this rule even exist by default?

Looks like here this rule might not be necessary here; you are right, the not file/not folder checks before the last rule would prevent anything existing in these folders from getting rewritten already.

I guess it is just used as a sort of “performance shortcut” here - doing a basic regex match on the requested URL is cheaper, than having to actually query the file system, “does this exist or not?”
So they apparently make the assumption here, that inside those “special” folders no rewriting will ever be necessary, they are data storage only.

So, yeah, if you want Typo3 handling your 404s for anything in these folders as well, then you should be able to remove/comment out this Rule.