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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