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60 lines
2.7 KiB
Markdown
60 lines
2.7 KiB
Markdown
# About Psalm
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<abbr title="PHP Static Analysis Linting Machine">Psalm</abbr> is a static analysis tool that attempts to dig into your program and find as many type-related bugs as possible.
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- [Introduction](#introduction)
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- [Installation](installation.md)
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- [Configuration](configuration.md)
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- [Running Psalm](running_psalm.md)
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- [Supported Annotations](supported_annotations.md)
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- [Dealing with code issues](dealing_with_code_issues.md)
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- [Typing in Psalm](typing_in_psalm.md)
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- [Plugins](plugins.md)
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- [Checking non-PHP files](checking_non_php_files.md)
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## Introduction
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Psalm tries to understand your codebase as best as possible so it can find errors.
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It has a few features that go further than other similar tools:
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- **Mixed type warnings**<br />
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If Psalm cannot infer a type for an expression then it uses a `mixed` placeholder. Any `mixed` type is a sign of an insufficiently-documented codebase. You can configure Psalm warn when encountering `mixed` types by adding *`totallyTyped="true"`* attribute to your XML config file.
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- **Logic checks**<br />
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Psalm keeps track of logical assertions made about your code, so `if ($a && $a) {}` and `if ($a && !$a) {}` are both treated as issues. Psalm also keeps track of logical assertions made in prior code paths, preventing issues like `if ($a) {} elseif ($a) {}`.
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- **Property initialisation checks**<br />
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Psalm checks that all properties of a given object have values after the constructor is called.
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- **Support for complicated array shapes**<br />
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Psalm has support for [object-like arrays](supported_annotations.md#object-like-arrays), allowing you to specify types for all keys of an array if you so wish.
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Psalm also has a few features to make it perform as well as possible on large codebases:
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- **Multi-threaded mode**<br />
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Using the `--threads=[X]` command line option will run Psalm's analysis stage on [X] threads. Useful for large codebases, it has a massive impact on performance.
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- **Incremental checks**<br />
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When using the `--diff` command line option, Psalm will only analyse files that have changed *and* files that reference them.
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## Example output
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```php
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// somefile.php
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<?php
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$a = ['foo', 'bar'];
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echo implode($a, ' ');
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```
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```bash
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> ./vendor/bin/psalm somefile.php
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ERROR: InvalidArgument - somefile.php:3:14 - Argument 1 of implode expects `string`, `array` provided
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```
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## Inspirations
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There are two main inspirations for Psalm:
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- Etsy's [Phan](https://github.com/etsy/phan), which uses nikic's [`php-ast`](https://github.com/nikic/php-ast) extension to create an abstract syntax tree
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- Facebook's [Hack](http://hacklang.org/), a PHP-like language that supports many advanced typing features natively, so docblocks aren't necessary.
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