[PHP] Replace deprecated Guzzle Utils::jsonEncode with native json_encode

[arjan-12b]

Fixes #24641

Guzzle 7.15 deprecated Utils::jsonEncode() / Utils::jsonDecode(), and Guzzle 8 removes them (upgrade guide). Generated PHP clients therefore emit deprecation warnings on Guzzle >= 7.15.

Change

Replaced the two \GuzzleHttp\Utils::jsonEncode() call sites (body param and form params) in both api templates:

-$httpBody = \GuzzleHttp\Utils::jsonEncode(ObjectSerializer::sanitizeForSerialization($pet));
+try {
+    $httpBody = json_encode(ObjectSerializer::sanitizeForSerialization($pet), JSON_THROW_ON_ERROR);
+} catch (\JsonException $e) {
+    throw new \InvalidArgumentException('json_encode error: ' . $e->getMessage(), 0, $e);
+}

• modules/openapi-generator/src/main/resources/php/api.mustache
• modules/openapi-generator/src/main/resources/php-nextgen/api.mustache

JSON_THROW_ON_ERROR is safe here: both generators already require php: ^8.1, and the response path in these same templates already decodes with json_decode($content, false, 512, JSON_THROW_ON_ERROR) — so encoding and decoding are now consistent.

This is fully backwards compatible

Utils::jsonEncode() was not a bare json_encode() — it checked json_last_error() and threw (src/Utils.php#L817). Dropping that error handling would silently send an empty body on an encode failure, so the encode calls catch \JsonException and rethrow as \InvalidArgumentException.

I verified parity by replicating Guzzle 7.15's implementation and diffing it against the generated code (PHP 8.4) — all cases match, on both output and failure:

Case	Old (Utils::jsonEncode)	New (generated)
object / nested / unicode / slashes / empty	identical JSON bytes	identical JSON bytes
invalid UTF-8	InvalidArgumentException: json_encode error: Malformed UTF-8 characters, possibly incorrectly encoded	same class, same message
INF	InvalidArgumentException: json_encode error: Inf and NaN cannot be JSON encoded	same class, same message

The message reproduces verbatim because Guzzle used json_last_error_msg() and JsonException::getMessage() returns the same text. And since GuzzleHttp\Exception\InvalidArgumentException extends SPL \InvalidArgumentException, existing catch (\InvalidArgumentException) blocks keep working — which is also the type the generated @throws docblocks already declare, so no PHPDoc changes are needed.

Notes

• No Utils::jsonDecode() usages existed in the templates, so only the encode side needed changing.
• Utils::tryFopen() / Utils::streamFor() in ObjectSerializer.mustache and FormDataProcessor.mustache are GuzzleHttp\Psr7\Utils, which is not deprecated — left untouched.
• Out of scope: composer.mustache still pins guzzlehttp/guzzle: "^7.3". Actually allowing Guzzle 8 needs that widened plus an audit of Guzzle 8's other BC breaks — happy to do that separately if wanted.

Testing

• Regenerated samples for php-OpenAPIClient, php-nextgen, php-nextgen-echo-api, php-nextgen-echo-api-streaming (17 files). The diff contains only the change above — no incidental regeneration churn.
• php -l (PHP 8.4) passes on all 17 regenerated files.
• Behavior parity against Guzzle 7.15 verified as tabled above.

PR checklist

• Read the contribution guidelines.
• Ran ./mvnw clean package and regenerated the affected samples. All changed files committed.
• @mentioning the PHP technical committee: @jebentier @dkarlovi @mandrean @jfastnacht @ybelenko @renepardon

[cubic-dev-ai]

All reported issues were addressed across 19 files

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