Disable nullable-to-nonnull-conversion on ExecuTorch (#19407)

[chatura-atapattu]

Summary:

On the Xcode 26.4 compiler upgrade, we error on:

fbsource//xplat/executorch/extension/apple:ExecuTorch (objcxx_compile ExecuTorch/Exported/ExecuTorchModule.mm (pic))
Local command returned non-zero exit code 1
Reproduce locally: `env -C "$(buck2 root --kind project)" -- 'BUCK_SCRATCH_PATH=buck-out/v2/tmp/fbsource/32bf73e24dec3a3 ...<omitted>... tion___0__/output_artifacts/__dep_files_intermediaries__/ExecuTorch/Exported/ExecuTorchModule.mm.pic (run `buck2 log what-failed` to get the full command)`
stdout:
stderr:
clang++: warning: argument unused during compilation: '-fstack-clash-protection' [-Wunused-command-line-argument]
xplat/executorch/extension/apple/ExecuTorch/Exported/ExecuTorchModule.mm:317:47: error: implicit conversion from nullable pointer 'NS_RETURNS_INNER_POINTER const char *' to non-nullable pointer type 'const char * _Nonnull' [-Werror,-Wnullable-to-nonnull-conversion]
  317 |   const auto errorCode = _module->load_method(methodName.UTF8String);
      |                                               ^```

Disable this error.

Differential Revision: D104463212

[pytorch-bot]

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❌ 1 New Failure, 3 Pending, 1 Unrelated Failure

As of commit 2aa8174 with merge base 29761c8 ():

NEW FAILURE - The following job has failed:

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  E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/o/openjpeg2/libopenjp2-7_2.4.0-6ubuntu0.4_amd64.deb 404 Not Found [IP: 172.66.152.176 80]

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[meta-codesync]

@chatura-atapattu has exported this pull request. If you are a Meta employee, you can view the originating Diff in D104463212.

[chatura-atapattu]

@pytorchbot label "release notes: none"

[shoumikhin]

Heads up: #19335 appears to address the same Xcode 26.4 issue with a different approach (inline ?: "" instead of pragma wrappers). Worth syncing before landing duplicate fixes.

[chatura-atapattu]

Heads up: #19335 appears to address the same Xcode 26.4 issue with a different approach (inline ?: "" instead of pragma wrappers). Worth syncing before landing duplicate fixes.

Yeah, this was one of the first solutions I got too generated by Claude. Wasn't sure whether we really wanted to return an empty string here, which in the future will likely be taken as intended behavior, vs the diagnostic push/pop that would warrant investigating further to fix the API and why its empty in the first place.

Will mention that in the diff, but in the end, both options get me my desired end state, so happy to go with either.

[shoumikhin]

One thing worth flagging on the pragma approach: those C++ methods take const std::string&, so the implicit conversion happens at the call site. If UTF8String ever did return NULL, std::string(nullptr) is undefined behavior (segfault on libc++ in practice). The pragma silences the warning but doesn't actually make the code safer. ?: "" at least avoids that path.

[chatura-atapattu]

I'm not much of a C++ expert, so I'm happy to defer to owners of the codebase.

Will close this pull request and look to the other change.