Report/Code: fix fatal potential fatal error when combined with Diff report

[jrfnl]

Description

Okay, so this is an awkward one.

If both the Code + the Diff report were requested + caching was turned on + the order of the requested reports was Code,Diff (i.e. first the code report), the following fatal error would occur:

Fatal error: Uncaught Error: Call to a member function getFixableCount() on null in path/to/PHP_CodeSniffer/src/Fixer.php:144
Stack trace:
#0 path/to/PHP_CodeSniffer/src/Reports/Diff.php(73): PHP_CodeSniffer\Fixer->fixFile()
#1 path/to/PHP_CodeSniffer/src/Reporter.php(285): PHP_CodeSniffer\Reports\Diff->generateFileReport(Array, Object(PHP_CodeSniffer\Files\LocalFile), true, 150)
#2 path/to/PHP_CodeSniffer/src/Runner.php(659): PHP_CodeSniffer\Reporter->cacheFileReport(Object(PHP_CodeSniffer\Files\LocalFile))
#3 path/to/PHP_CodeSniffer/src/Runner.php(400): PHP_CodeSniffer\Runner->processFile(Object(PHP_CodeSniffer\Files\LocalFile))
#4 path/to/PHP_CodeSniffer/src/Runner.php(119): PHP_CodeSniffer\Runner->run()
#5 path/to/PHP_CodeSniffer/bin/phpcs(30): PHP_CodeSniffer\Runner->runPHPCS()
#6 {main}
  thrown in path/to/PHP_CodeSniffer/src/Fixer.php on line 144

To reproduce the issue (on master):

1. Create a small test file like:

   <?php
   
   echo 'hello'.callMe( $p );

2. Run the following command to initialize the cache:

   phpcs -ps ./test.php --standard=PSR2 --report=Code,Diff --cache

   All should be fine.
3. Now run the same command again and see the fatal error.

Some investigating later, it turns out that both the Code report, as well as the Diff report, re-parse the current file, with the Diff report initializing the fixer once the file has reparsed, but the Code report not doing so (as it doesn't need the fixer). The problem with that is that the Code report basically leaves the Fixer in an invalid state, leading to the above error.

While it is up for debate whether reports should ever (be allowed to) re-parse files, for now, let's fix the fatal.

Re-evaluating the report setup should definitely be done, but should probably wait until the Reports classes have test coverage.

Suggested changelog entry

Prevent a potential race condition when both the Diff + the Code reports are requested and caching is on.

Types of changes

• Bug fix (non-breaking change which fixes an issue)