Recursively finds and fixes unquoted array keys in PHP. This is not full-proof, nor does it cover 100% of all occurrences, but it gets really close at getting nearly all of them. See the respective sources for discussion and limitations of each function.

fix_unquoted_array_keys.php

#!/usr/bin/php
<?php
/**
 * Run this script on the command line like `php fix_unquoted_array_keys.php './*.php'`
 * Or make the file executable and run it directly.
 *
 * As the first argument after the script name gets passed directly to `rglob()`, it's
 * recommended that you quote it to prevent the shell from doing the expansion itself.
 */


/**
 * Gets an array of PHP blocks from a string.
 *
 * @param string $content The code to check.
 * @return array The array of PHP code blocks.
 */
function get_php_blocks($content) {
	$blocks = [];
	$len = strlen($content);
	$cursor = 0;

	do {
		$stepper = '';
		$try_again = false;

		do {
			// find the block
			$matches = [];
			if ($found = preg_match('/(<\?(?:=|php\s).+?'.$stepper.'(?:\?>|$))/ms', $content, $matches, PREG_OFFSET_CAPTURE, $cursor)) {
				// make sure the end is valid
				$tokens = @token_get_all($matches[0][0]);
				$last = array_pop($tokens);
				$try_again = // try again if...
					($matches[0][1] + strlen($matches[0][0])) < $len // we're not at the end of the string
					&& (
						!is_array($last) // it's not a single character
						|| $last[0] !== T_CLOSE_TAG // it's not a close tag
					);
			} else {
				$try_again = false;
			}

			if ($try_again) {
				// add to the stepper
				$stepper .= '\?>.+?';
			} elseif ($found) {
				// record the block
				$blocks[] = $matches[0][0];

				// update the offset
				$cursor = $matches[0][1] + strlen($matches[0][0]); // offset + length
			} else {
				// there's no more php to search for
				$cursor = $len;
			}
		} while ($try_again);

	} while ($cursor < $len);

	return $blocks;
}

/**
 * Does the actual work of fixing the unquoted keys.
 *
 * @param string $content The content of the file to fix.
 * @param int &$count The number of changes `preg_replace()` made.
 * @return string The updated content.
 * 
 * @see https://stackoverflow.com/a/36753232
 * @see https://www.php.net/manual/en/language.variables.basics.php
 * @see https://stackoverflow.com/a/75590499/3404349
 */
function fix_unquoted_array_keys($content, &$count = 0) {
	// get all php blocks
	$blocks = get_php_blocks($content);
	foreach ($blocks as $block) {
		// do replacements for the first index level
		$orig_block = $block;
		$block = preg_replace('/^!|\$([a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*)\[([a-zA-Z_][a-z0-9_]+)\]/','\$$1[\'$2\']', $block, -1, $c1);
		$count = $c1;

		// do replacements for subsequent index levels
		$block = preg_replace('/\]\[([a-zA-Z_][a-z0-9_]+)\]/', '][\'$1\']', $block, -1, $c2);
		$count += $c2;

		// find double-quoted strings
		if ($count > 0) {
			$block = preg_replace_callback('/\/\*.*?\*\/(*SKIP)^|\/\/.*?$(*SKIP)^|\'(?>\\\\?.)*?\'(*SKIP)^|"(?>\\\\?.)*?"/ms', function ($matches) {
				// add brakets to array key references in the string
				return preg_replace('/(?<![{\\\\])(\$\w+(?:\[\'\w+\'\]){1,})/', '{$1}', $matches[0]);
			}, $block);
		}

		// update it
		$content = str_replace($orig_block, $block, $content);
	}

	return $content;
}

/**
 * The "manager" of updating and checking the file.
 *
 * @param string $filename The path to the file to fix
 * @param int $count How many occurrences were updated
 * @return string The status
 */
function fix_file($filename, &$count = 0) {
	// get file
	if (!is_file($filename)) {
		return "Not a valid file!";
	}
	$content = file_get_contents($filename);

	// do the work
	try {
		$content = fix_unquoted_array_keys($content, $count);
	} catch (Throwable $e) {
		return $e->getMessage();
	}

	// put it back
	file_put_contents($filename, $content);

	// check the file just in case we broke something
	@exec("php -l ".$filename." 2>&1", $syntax);
	if ($syntax[0] && strpos($syntax[0], "No syntax errors") === false) {
		return $syntax[0];
	}

	return "OK";
}

/**
 * Calls `glob()` recursively and returns all files and folders matching `$pattern`.
 *
 * @param string $pattern The glob pattern to search for.
 * @param int $flags Flags supported by `glob()` (except for GLOB_BRACE).
 * @return array The list of files and folders.
 * 
 * @see https://stackoverflow.com/a/17161106
 */
function rglob($pattern, $flags = 0) {
	$files = glob($pattern, $flags); 
	foreach (glob(dirname($pattern).'/*', GLOB_ONLYDIR | GLOB_NOSORT) as $dir) {
		$files = array_merge(
			[],
			...[$files, rglob($dir . "/" . basename($pattern), $flags)]
		);
	}
	return $files;
}

// skip this file
array_shift($argv);

// recursively go through files from input
$files = $changed = $fixes = 0;
foreach ($argv as $param) {
	foreach (rglob($param) ?: [] as $file) {
		if (is_dir($file)) {
			continue;
		}

		// trackers
		++$files;
		$total = 0;

		// do the fix
		$status = fix_file($file, $total);
		echo "{$file}\t{$status} ({$total})".PHP_EOL;

		// more trackers
		$total === 0 ?: ++$changed;
		$fixes += $total;

		// exit early if there's an error
		if ($status !== 'OK') {
			break 2;
		}
	}
}

echo "\nUpdated {$fixes} occurences in {$changed} files (out of {$files} files scanned).\n";