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83 lines
2.7 KiB
Markdown
83 lines
2.7 KiB
Markdown
# Things that make developing Psalm complicated
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This is a somewhat informal list that might aid others.
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## Type inference
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Type inference is one of the big things Psalm does. It tries to figure out what different PHP elements (function calls, if/for/foreach statements etc.) mean for the data in your code.
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Within type inference there are a number of tricky areas:
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#### Loops
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Loops are hard to reason about - break and continue are a pain. This analysis mainly takes place in `LoopAnalyzer`
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#### Combining types
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There are lots of edge-cases when combining types together, given the many types Psalm supports. Type combining occurs in `TypeCombiner`.
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#### Logical assertions
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What effect do different PHP elements have on user-asserted logic in if conditionals, ternarys etc. This logic is spread between a number of different classes.
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#### Generics & Templated code
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Figuring out how templated code should work (`@template` tags) and how much it should work like it does in other languages (Hack, TypeScript etc.) is tricky. Psalm also supports things like nested templates (`@template T1 of T2`) which makes things trickier
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## Detecting dead code
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Detecting unused variables requires some fun [data-flow analysis](https://psalm.dev/articles/better-unused-variable-detection).
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Detecting unused classes and methods between different runs requires maintaining references to those classes in cache (see below).
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## Supporting the community
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- **Supporting formal PHPDoc annotations**
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- **Supporting informal PHPDoc annotations**
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e.g. `ArrayIterator|string[]` to denote an `ArrayIterator` over strings
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- **non-Composer projects**
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e.g. WordPress
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## Making Psalm fast
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#### Parser-based reflection
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Requires scanning everything necessary for analysis
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#### Forking processes** (non-windows)
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Mostly handled by code borrowed from Phan, but can introduce subtle issues, also requires to think about how to make work happen in processes
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#### Caching thing
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see below
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## Cache invalidation
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#### Invalidating analysis results
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Requires tracking what methods/properties are used in what other files, and invalidating those results when linked methods change
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#### Partial parsing
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Reparsing bits of files that have changed, which is hard
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## Language Server Support
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#### Handling temporary file changes
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When files change Psalm figures out what's changed within them to avoid re-analysing things unnecessarily
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#### Dealing with malformed PHP code
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When people write code, it's not always pretty as they write it. A language server needs to deal with that bad code somehow
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## Fixing code with Psalter
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#### Adding/replacing code
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Figuring out what changed, making edits that could have been made by a human
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#### Minimal diffs
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hard to change more than you need
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