Fix #13569: Catching undefined constant causes dead catch false positive

[phpstan-bot]

Summary

Dynamic class constant fetches like ReactionType::{$name} can throw \Error at runtime when the constant name doesn't exist. PHPStan was reporting a false positive "Dead catch - Error is never thrown in the try block" because no throw point was registered for dynamic class constant fetch expressions.

Changes

• Added an implicit throw point when processing Expr\ClassConstFetch with a dynamic name ($expr->name instanceof Expr) in src/Analyser/NodeScopeResolver.php
• Added regression test in tests/PHPStan/Rules/Exceptions/data/bug-13569.php and test method in tests/PHPStan/Rules/Exceptions/CatchWithUnthrownExceptionRuleTest.php

Root cause

In NodeScopeResolver::processExprNode(), when handling Expr\ClassConstFetch, the code correctly processed sub-expressions (the class and name expressions) but did not add an implicit throw point for the fetch itself when the name was dynamic. Since the constant name is determined at runtime, accessing a non-existent constant throws \Error. Without this throw point, the dead catch detection rule incorrectly concluded that \Error could never be thrown in the try block.

Test

The regression test uses an enum with a tryFromName method that uses ReactionType::{$name} inside a try/catch block catching \Error. The test verifies no dead catch error is reported.

Fixes phpstan/phpstan#13569

[VincentLanglet]

I already close it because of #5096 (comment)