Makes sense to me 👍 Ping me please once you mark it as ready.

@ondrejmirtes
I think I can mark this ready and continue refactoring in a different PR.
What I'm wondering is that these lines of changes (specifying same type with phpdoc type and native type to keep the current behavior)
https://github.com/phpstan/phpstan-src/pull/1372/files#diff-0c3f50d118357d9cb6d6f4d0eade75b83797d57056ff3b9c58ec881a13eaa6feL1806-R1922
is not always correct? and we have to create native type to specify separately every time we call specifyExpressionType

What I'm thinking right now is that adding a bool parameter to getType with a default value of $treatPhpDocTypesAsCertain (is this a BC break?) which can switch between phpdoc types and native types with just by branching out in one place. (Maybe $nativeExpressionTypes can be deleted?)

My idea is that there's Scope::getType() and Scope::getNativeType(). In the future it'd be great if Scope::getNativeType() answered truthfully even about expressions like MethodCall.

Let's say we have:

/** @return positive-int */
public function doFoo(): int
{
}

Scope::getType(MethodCall) would answer positive-int, but Scope::getNativeType(MethodCall) would answer just int.

It doesn't matter much to me if it's done via some boolean parameters, or by code duplication. I'm more fan of code duplication because it's more easier to maintain in the future :)

So - if you're interested in $treatPhpDocTypesAsCertain=true, call Scope::getType(), if false, call Scope::getNativeType(). Can you imagine this working? Thanks :)

Also - it's not exactly the same thing, but today you can call $scope->doNotTreatPhpDocTypesAsCertain()->getType(...) - it's used in a few places.

Also, once Scope::getNativeType() truthfully answers to all expressions, we can do a really cool new rule:

/** @var string $foo */
$foo = $this->returnsInt(); // has int in native return type

We can mark this @var as always wrong :)

Thank you.

Also - it's not exactly the same thing, but today you can call $scope->doNotTreatPhpDocTypesAsCertain()->getType(...) - it's used in a few places.

Oh, I was not aware of this. Thanks!

@ondrejmirtes

Thank you very much for your comments, I'll take them into account 👍

Let's say we have:
/** @return positive-int */
public function doFoo(): int
{
}
Scope::getType(MethodCall) would answer positive-int, but Scope::getNativeType(MethodCall) would answer just int

I'm a little confused with this comment, maybe not understanding what "native type" is correctly.
I was thinking that "native type" should not refer to the PHPDocs.

Yes, I don't see any contradiction in that :) "Native type" is a type we can rely on, it doesn't take PHPDocs into account.