Static analysis: Using $this in a static method should show an error

[MaartenStaa]

Closes #476

Two scenarios produce errors, either $this is used in a static method (as described in the issue), or when it's used outside of a class method altogether, e.g.:

<?php

class A
{
    public static function foo()
    {
        return $this; // error here
    }

    public function bar()
    {
        return $this; // no error here (of course)
    }
}

function foo()
{
    return $this; // error here
}

echo $this; // error here

[codecov]

Codecov Report

Merging #528 into master will increase coverage by 0.47%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #528      +/-   ##
============================================
+ Coverage     78.91%   79.38%   +0.47%     
- Complexity      832      837       +5     
============================================
  Files            56       56              
  Lines          1968     1979      +11     
============================================
+ Hits           1553     1571      +18     
+ Misses          415      408       -7

Impacted Files	Coverage Δ	Complexity Δ
src/TreeAnalyzer.php	94.64% <100%> (+0.58%)	54 <0> (+5)	⬆️
src/DefinitionResolver.php	84.05% <0%> (+1.12%)	302% <0%> (ø)	⬇️
src/Cache/FileSystemCache.php	27.27% <0%> (+4.54%)	8% <0%> (ø)	⬇️

[felixfbecker]

Could you add a test for this?

[jens1o]

Should this be included in the parser instead?

[MaartenStaa]

@jens1o see #476, I asked the same question.

edit: as php -l itself does not produce a parse error either for this, it makes sense that the parser would not produce an error diagnostic.

[felixfbecker]

This is awesome