Resolve bootstrap autoloaders' classes from the files they ask for, running them for real only when that cannot redeclare a symbol

[ondrejmirtes]

The function_exists($className) gate added for phpstan/phpstan#14988 confused two meanings of "functions": AutoloadFunctionsSourceLocator is about autoload functions — the spl_autoload_register() callbacks that bootstrap files register — not about class names coinciding with defined functions. Executed for a class, such an autoloader either asks for a file, which the file-read trap detects, or defines the class without one, through class_alias() or eval().

The gate's probe also poisoned its own evidence: a trapped include succeeds with empty content, defining nothing but still registering in get_included_files(), so comparing the trapped files against get_included_files() taken after the probe declined the very lookup it was probing. Laravel's facade aliases whose target class is not loaded yet hit exactly that: resolving Redirect makes class_alias() ask for the file of Illuminate\Support\Facades\Redirect, the probe trapped that read, found the file "already included" and declined — and larastan's monicahq/monica e2e failed with seven unknown class Redirect errors on 2.2.9 and current 2.2.x. Any earlier probe trapping the same file poisoned later lookups the same way, since the pseudo-include sticks for the rest of the process; include-list bookkeeping cannot be made sound.

Now every class lookup through this locator works the same way:

1. Probe the autoload functions under the file-read trap. One that defines the class without reading a file has already done its work.
2. Locate the class statically in the files they asked for (AutoloadSourceLocator::locateIdentifierInFiles()) — a plain include-based autoloader resolves with no execution at all.
3. Run the autoloaders for real only as a fallback — the alias-of-unloaded-target case, where the trapped file is the target's and never declares the alias name — and only when wouldIncludingFilesRedeclareSymbols() says executing the located files cannot fatally redeclare a currently defined class or function. That is the actual #14988 hazard, judged by the files' statically parsed symbols, which pseudo-includes cannot poison.

The new e2e/bug-15102c covers the shape Illuminate\Foundation\AliasLoader creates in a real Laravel app: a prepended autoloader aliasing a name that collides with a global helper function (Redirect vs redirect()) to a class only Composer can autoload. It fails on current 2.2.x and passes with this change. bug-15102, bug-15102b, bug-14988, bug-12972b and bug-12972c still pass (verified with cleared result caches), and the full monicahq/monica + larastan analysis is clean against this branch.

See phpstan/phpstan#15102

🤖 Generated with Claude Code

https://claude.ai/code/session_01JkCjnojdWZvswKCPmzt4zY

[ondrejmirtes]

FYI reverting this: #6292.

#15102 keeps working.