Tokenizer: fatal error when a const name is the last non-empty token in a file #1451

Describe the bug

PHPCS aborts with a fatal "Undefined array key" error while tokenizing a file when the name of a const declaration is the last non-empty token in the file (const NAME with nothing following it).

Code sample

<?php

const A

To reproduce

Steps to reproduce the behavior:

1. Create a file called test.php with the code sample above.
2. Run phpcs test.php (the standard is irrelevant).
3. See the error message displayed:

FILE: test.php
--------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
--------------------------------------------------------------------------------
 1 | ERROR | An error occurred during processing; checking has been aborted.
   |       | The error message was: Undefined array key 6 in
   |       | src/Tokenizers/PHP.php on line 2583
--------------------------------------------------------------------------------

Expected behavior

I would expect PHPCS to tokenize the file without a fatal error, so that the rest of the file can still be checked.

Versions

Additional context

When $insideConstDeclaration is true, a loop walks forward from the constant name to the next non-empty token and then checks whether that token is an =:

When the constant name is the last non-empty token in the file, the for loop ends via its $i < $numTokens condition with $i equal to $numTokens. The following $tokens[$i] === '=' check then reads an index that does not exist, which triggers the "Undefined array key" error.

The constant-handling code involved was added in #321 (support for typed OO constants).

Please confirm

• I have searched the issue list and am not opening a duplicate issue.
• I have read the Contribution Guidelines and this is not a support question.
• I confirm that this bug is a bug in PHP_CodeSniffer and not in one of the external standards.
• I have verified the issue still exists in the 4.x branch of PHP_CodeSniffer.