Resolve nested PHPDoc unions in linear time

[SanderMuller]

MockObjectTypeNodeResolverExtension resolved every member of a union before it found that the union holds no mock class. TypeNodeResolver then resolved the same union again, so each nesting level of a PHPDoc union doubled the work.

Now the extension resolves only the direct identifier members first. It resolves the whole union only when one of them is a mock class. Identifiers have no children, so resolving them twice costs a constant amount per member.

Measured with PHPStan 2.2.16 on a file with one nested union, /** @var ((((int|string)|string)|string)|string) $x */ at increasing depth, level 9, single process, one run each:

depth	before	after	without the extension
18	1.6s	1.0s	1.0s
20	5.0s	1.0s	1.3s
21	6.2s	1.0s	1.1s
22	11.3s	1.0s	1.2s
30		1.0s

The inferred types do not change. Before the fix I dumped the types of six mock unions and one union without a mock, and the new test pins those types. The mock unions are MockObject|Foo, the same name with a leading backslash, a use ... as alias, Stub|Foo, a local @phpstan-type alias, and a mock union nested in (...)|null. A type alias from the global typeAliases config also still gives the intersection. The check runs on the resolved identifier, not on its name.

The test also has a depth-30 union without a mock, and a depth-30 union with a mock at the centre. Before the fix it was still running after 90 seconds. With the fix it runs in 0.1s.

🤖 Generated with Claude Code

[ondrejmirtes]

Thank you!