PHP to Hack at Slack
- 1. Scott Sandler - June 2019
- 2. Scott Sandler Senior Staff Engineer @ Slack 2015 - Present
- 9. ● Static type checker, hh_client ● Language Server Protocol ● VSCode, VIM, Emacs, and more ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 10. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 11. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 12. “Generic programming is a style of computer programming in which algorithms are written in terms of types to-be-specified-later that are then instantiated when needed for specific types provided as parameters.” - Wikipedia Type Parameters like <T> allow classes, functions, and data structures to act on multiple types ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 13. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 14. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 15. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 16. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 17. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 18. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 19. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 20. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 21. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 22. ● Represent an array with known structure ● Named keys with known data types ○ Keys can be optional ● Structural subtyping ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 23. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 24. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 25. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 26. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 28. ● Inconsistent Argument Order ○ array_map($callback, $array); ○ array_filter($array, $callback); ● Misleading return types ○ strpos() returns int OR false ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 29. Read from inside out… or split into multiple lines and name each intermediate value? ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 30. ● Consistent Argument Order ● Consistent Return Types ○ null instead of false ● Namespaces: ○ Container Functions: Vec*, Dict*, Keyset*, C* ○ Basics: Str*, Regex*, Math* ○ More: IO*, PseudoRandom*, SecureRandom* ● |> Pipeline operator for chaining function calls ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 31. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 32. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 33. ● Overview ● Static Type Checking ● Generics ○ Arrays ○ Hack Arrays ○ Shapes ● Standard Library ○ Pipeline ○ Typed Regex ● XHP
- 34. ● async/await cooperative multi-tasking ● is/as keywords for type assertion ● lambdas ● enums ● <<__Memoize>> caching ● hackfmt ● Function Autoloading ● VSCode debugging
- 35. Migrating Slack
- 37. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 38. Fix hh_client errors ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 39. ● Hundreds of bugs ● Convince typechecker ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 40. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 41. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 42. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 43. New Linter: HHAST ● Hack Abstract Syntax Tree ● More rigorous linters ● Migrations as well Old Linter: PHP_CodeSniffer ● Stream of tokens ● Each linter is a mini-PHP parser ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 44. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 46. After: AsyncMysqlClient ● Shapes for each table ● Async queries Before: mysqli ● Untyped arrays of strings ● Synchronous queries ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 47. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 48. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 49. ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 50. Untyped code ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 51. Untyped code ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 52. Type Coverage
- 53. Colorized Type Coverage ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 54. Coverage Numbers ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 55. Track it and pipe it to Slack ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 56. <?hh // strict 1. All functions and arguments must be typed 2. No top-level code 3. Other dynamicism like $GLOBALS banned ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 57. Eliminate PHP Dependencies 1. Smarty to XHP migration ○ Smarty Parser -> hack-codegen 2. Other dependencies: ○ Convert to Hack ○ Remove dependency ○ Run as PHP7 web service ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 58. HHVM 4.0 Upgrade ● <?php to <?hh ● Fix hh_client errors ● Blocking CI tests ○ hh_client ○ Linter ● Move code into functions ● Foundational Types ○ DB Shapes ○ Inferred returns ○ Untyped code ● Coverage Competition ● <?hh // strict ● Eliminate PHP deps ● HHVM 4.0 upgrade
- 60. ● Thousands of bugs found and fixed ● Entire classes of problems eliminated ○ Call to undefined function ○ Missing include/require ○ Missing array keys ○ Missing null checks
- 61. ● Developer Surveys ● Increased confidence ● Increased productivity ● “When the type checker passes, my code usually works on the first try”
- 65. ● Types are the cheapest unit test ○ ...but only when you have a lot of them ● Types are the cheapest documentation ○ Especially complex types like shapes ● Typing is best done as part of feature work Lessons Learned
- 68. Yes, this is possible ● Generics RFC ● Arrow functions in 7.4 ● Property type hints ● JIT in PHP8 ● Static analysis: ○ phan: https://github.com/phan/phan ○ phpstan: https://github.com/phpstan/phpstan ○ psalm: https://github.com/vimeo/psalm
- 69. ● eval(), create_function(), extract(), compact() ● $GLOBAL variables ● $$variable variables ● call_user_func() ● &$references Avoid PHP’s most dangerous features