ext/spl: Fix default argument handling for named parameters in SplFileObject::fgetcsv()

[arshidkv12]

#22156

[devnexen]

Hi @arshidkv12 thanks for looking into but I m afraid it's more a band aid than a fix (and even it is incomplete). e.g. ; is not the only valid csv separator.

[arshidkv12]

You are correct. I think this should be changed in the stub.php file. Then manually assign the default value if it is null..

public function fgetcsv(string $separator, string $enclosure, string $escape): array|false {}

[devnexen]

A few suggested tests to add so the brittleness of the current approach is visible in CI.

1. Explicit , after a non-comma setCsvControl (the false-negative the guard creates).**

$f->setCsvControl(';', "\n", "\\");
$f->fwrite("a,b;c\n");
$f->seek(0);
var_dump($f->fgetcsv(',', '"', '\\'));   // user explicitly wants ,
// expected: ["a","b;c"]   patched: ["a,b","c"]   ← regression introduced by this PR

2. Enclosure-only via named arg (the bug is unfixed on enclosure).
$f->setCsvControl(',', "'", "\\");
$f->fwrite("a,'b,c'\n");
$f->seek(0);
var_dump($f->fgetcsv(escape: '\\'));     // named-skip fills enclosure with "
// expected: ["a","b,c"]   patched: ["a","'b","c'"]

3. Escape via named arg with a non-default enclosure (also exercises the is_escape_default deprecation path).
$f->setCsvControl(',', "'");
$f->fwrite("a,'b\\'c'\n");
$f->seek(0);
var_dump($f->fgetcsv(escape: '\\'));     // enclosure silently becomes "

4. Same bug shape on fputcsv() (the PR does not touch it).
$f->setCsvControl(';', "\n", "\\");
$f->fputcsv(['a','b'], escape: '\\');
$f->seek(0);
echo $f->fgets();                         // expected "a;b\n"   patched: "a,b\n"

5. Reflection round-trip to lock the API contract.
$rm = new ReflectionMethod(SplFileObject::class, 'fgetcsv');
foreach ($rm->getParameters() as $p) {
    var_dump($p->getName(), $p->allowsNull(), $p->getDefaultValue());
}

6. is_escape_default invariant. After setCsvControl(',', '"') (two args), fgetcsv() (no args) should still emit the escape-default deprecation. Confirms the rewrite
does not accidentally suppress the existing notice through the nullability change.

Two meta-points:
- The PR's own test calls setCsvControl(';', "\n", "\\") (three args), which flips is_escape_default to false and hides cases 3 and 6. Dropping the third arg from
setCsvControl already changes what is exercised, so both shapes are worth covering.
- Worth a quick run against the standalone fgetcsv() / fputcsv() in ext/standard as well, just to confirm those are unaffected (no instance state to clobber there),
so the fix scope is correctly limited to the SPL methods.

Note: suggested test cases with help of LLM.

[devnexen]

For final review, might be best to wait Gina's opinion not enough familiar with this part of the code :)

[arshidkv12]

I can fix fputcsv after completing this PR.