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PHPStan Levels and Baselines

PHPStan 376,908 (github.com/phpstan/phpstan (https://github.com/phpstan/phpstan 14,112 ), 2.2.14 of 12 September 2026, composer require --dev phpstan/phpstan) has rule levels 0 to 10, each adding checks, so old code can start low. Errors in Invoice from phpstan analyse --level=N:

PHPStan errors found in Invoice.php by level
Level Adds (PHPStan docs) Errors
0-4 Unknown symbols, PHPDocs, return types, dead code 1
5 Argument types 2
6-7 Missing type declarations, partly wrong unions 4
8-9 Nullable access, explicit mixed 5
10 Implicit mixed (new in 2.0) 10

Level 8 suits new code. On old code, phpstan analyse --generate-baseline records today's errors (here 5) in phpstan-baseline.neon; include it, and CI fails only on new ones:

phpstan.neon: level 8, with the baseline includedYAML
includes:
  - phpstan-baseline.neon
parameters:
  level: 8
  paths:
    - src

The next day someone adds Coupon, which calls $cart->total(). The old errors stay silent:

Output of 230
...
  8      Call to an undefined method Acme\Shop\Cart::total().  
         🪪  method.notFound                                   
...

// @phpstan-ignore method.notFound silences one check on one line; fixed baseline entries are reported as stale, so the baseline only shrinks.