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psalm/docs/what_makes_psalm_complicated.md
2019-02-11 18:39:19 -05:00

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Things that make developing Psalm complicated

This is a somewhat informal list that might aid others.

Statement analysis

  • Type inference
    what effect do different PHP elements (function calls, if/for/foreach statements etc.) have on the types of things
  • Especially loops
    loops are hard to reason about - break and continue are a pain
  • Also dealing with literal strings/ints/floats
  • Code liveness detection
    what effect do different PHP elements have on whether code is in scope, whether code is redundant
  • Logical assertions
    what effect do different PHP elements have on user-asserted logic in if conditionals, ternarys etc.
  • Generics & Templated code
    Figuring out how templated code should work (@template tags), how much it should work like it does in other languages (Hack, TypeScript etc.)

Supporting the community

  • Supporting formal PHPDoc annotations
  • Supporting informal PHPDoc annotations
    e.g. ArrayIterator|string[] to denote an ArrayIterator over strings
  • non-Composer projects
    e.g. WordPress

Making Psalm fast

  • Parser-based reflection
    requires scanning everything necessary for analysis
  • Forking processes (non-windows)
    mostly handled by code borrowed from Phan, but can introduce subtle issues, also requires to think about how to make work happen in processes
  • Caching things
    see below

Cache invalidation

  • Invalidating analysis results
    requires tracking what methods/properties are used in what other files, and invalidating those results when linked methods change
  • Partial parsing
    Reparsing bits of files that have changed, which is hard

Language Server Support

  • Making Psalm fast
    see above
  • Handling temporary file changes
  • Dealing with malformed PHP code
    When people write code, it's not always pretty as they write it. A language server needs to deal with that bad code somehow

Fixing code with Psalter

  • Adding/replacing code
    Figuring out what changed, making edits that could have been made by a human
  • Minimal diffs
    hard to change more than you need