Blocklisted file-extension patterns are unanchored, so ordinary filenames fail the check

Description

Check_File_Check matches its blocklist with preg_grep and no anchors, so a pattern intended to match a file extension matches that string anywhere in the path.

// checks/class-file-check.php
$blocklist = array(
    …
    '\.dat' => __( 'Customizer import file', 'theme-check' ),
    '\.xml' => __( 'XML file', 'theme-check' ),
    '\.sh'  => __( 'Shell script file', 'theme-check' ),
    …
);

foreach ( $blocklist as $file => $reason ) {
    if ( $filename = preg_grep( '/' . $file . '/', $filenames ) ) {

'\.sh' is the worst of these because sh begins many ordinary words. Any CSS or JS file whose name contains .sh… is reported as a shell script and raises a REQUIRED error, which fails the automated scan on upload.

Step-by-step reproduction instructions

1. Add a stylesheet named assets/styles/tokens.sys.shape.css to any theme.
2. Run Theme Check.

Expected: no error; it is a CSS file.

Actual:

REQUIRED: tokens.sys.shape.css Shell script file found. This file must not be in the production version of the theme.

Scope

Four patterns produce false positives on plausible filenames:

.shape, .sheet, .shortcodes, .shadow, .database, and .sqlite3 are all normal names. shape in particular is the name of one of Material Design's token axes, so tokens.sys.shape.css is a natural filename for any theme following that system.

Suggested fix

Anchor the extension patterns at the end of the string:

if ( $filename = preg_grep( '/' . $file . '$/', $filenames ) ) {

That suits every entry that is an extension. Three entries are not extensions and would need care: '^.+[a-zA-Z0-9]' (hidden files, already anchored at the start), 'error_log', and '__MACOSX'. Splitting the blocklist into “extension” and “exact name” groups, each matched with its own anchoring, would be clearer than one array with mixed semantics.

Environment info

• Theme Check 20260901
• WordPress 7.1
• PHP 8.3

Start in checks/class-file-check.php at the blocklist and preg_grep call, then run Theme Check with the reproduction filename assets/styles/tokens.sys.shape.css. Keep extension matching limited to the end of the path while preserving the distinct hidden-file, error_log, and __MACOSX cases; done means the listed ordinary filenames pass without allowing blocked extensions through.