concat without assigment

[staabm]

Feature request

today I stumbled over a bug, in which someone missed to echo the result of a string-concatenation, effectively producing a useless concatenation.

would be great if phpstan could error about the concat beeing useless:
https://phpstan.org/r/b76066d6-5fb9-440b-a1f2-16651b6a062d

same could be true for other operations when no assignment is done
https://phpstan.org/r/ae8ba301-436a-4945-aa39-181d7536620c

Did PHPStan help you today? Did it make you happy in any way?

No response

[lulco]

I'd do this as rule for BinaryOp using its attribute parent, but this attribute is no longer available. What is current best practice?

[lulco]

I found ParentStmtTypesVisitor and it seems to be similar to what I want. So is this the way? Write visitor first and then use attribute? It looks I will need just to check if ParentNodeType is PhpParser\Node\Stmt\Expression

[staabm]

At least thats what I had in mind on how to implement it.

Create a new visitor and store in attributes what is required to make the rule work

[lulco]

I've implemented it this way, please check phpstan/phpstan-src#2858

[ondrejmirtes]

One way to look at this feature request is that it needs to be implemented in NoopRule where similar nodes are handled. And it would lead to simple code like 'a' . 'b'; being reported.

So it can definitely be added there in NoopRule.

But the underlying issue is much more complex. When you consider 'No'. $this->doSomething() you need to make sure that doSomething method is pure. And you need to actually implement that for all expression types.

And at that point this feature request should be implemented as well: #4426 (reporting that @phpstan-pure above a function isn't true because the function does something impure).

This needs to be done in NodeScopeResolver and be decided for all expressions and statements.

ExpressionResult and StatementResult need to get a new method describing whether they are pure or not.

Last time this was done was with "throw points". If you Ctrl+F in NodeScopeResolver for throwPoints, it yields about 400 results. That's the scope if this task :)

I'd appreciate if someone tackled this, in small steps.

[lulco]

I see it is not that simple I thought. NodeScopeResolver is out of my knowledge :)

[ondrejmirtes]

Done as part of bleeding edge thanks to impure points: phpstan/phpstan-src@a647052

Please note that functions/methods need @phpstan-pure annotation to make sure this is detected correctly.

[staabm]

@ondrejmirtes nice, thank you.

one note: I wonder why line 10 did not error:
https://phpstan.org/r/24869b6d-8b20-4542-a763-a4192e044b09

all other lines look great

[ondrejmirtes]

Because it might throw DivisionByZeroError. So it's not really "side effect-free" if you want to perform it in order to throw an exception.

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