[Cocoa] Fix deprecated SEL cast in sel_registerName (issue #3186)

[HeikoKlare]

Issue

Clang emits a -Wcast-of-sel-type deprecation warning in the auto-generated os.c when sel_registerName returns a SEL that is directly cast to jlong:

rc = (jlong)sel_registerName(lparg0);
// warning: cast of type 'SEL _Nonnull' to 'jlong' (aka 'long') is deprecated;
//          use sel_getName instead [-Wcast-of-sel-type]

This warning is part of a broader set of deprecation warnings in the macOS/Cocoa native implementation tracked in issue #3186. Eliminating all such warnings is a prerequisite for enabling -Werror in the native build.

Solution options considered

Several approaches were investigated before arriving at the final solution.

❌ Direct intermediate cast: (jlong)(uintptr_t)sel_registerName(...)

Adding an intermediate uintptr_t cast does not help — the compiler treats any cast from a SEL value to any type (integer or pointer) as deprecated:

warning: cast of type 'SEL _Nonnull' to 'uintptr_t' (aka 'unsigned long') is deprecated;
         use sel_getName instead [-Wcast-of-sel-type]

Same result with void* or const char* as intermediate types — the -Wcast-of-sel-type warning fires for any explicit cast from a SEL value regardless of the target type.

❌ Using sel_getName: (jlong)(uintptr_t)sel_getName(sel_registerName(...))

The compiler's suggestion — routing through sel_getName(SEL) → const char* — eliminates the deprecated cast. This was implemented via flags=no_gen in OS.java and a hand-written function body in os_custom.c. It works correctly, but has two drawbacks: it calls an extra runtime function and moves the implementation out of the auto-generated os.c into os_custom.c, which is harder to maintain.

Note: the build in the aarch64 fragment folder regenerates os.c from OS.java annotations on each run, so any annotation-based approach must work with the compiled JNI generator in the Maven toolchain — not just the source.

✅ Function-pointer cast: ((jlong (*)(const char*))sel_registerName)(lparg0)

The fix applies the same pattern SWT already uses for all objc_msgSend variants. Instead of casting the value returned by sel_registerName, the function pointer itself is cast to declare a different return type:

rc = (jlong)((jlong (*)(const char*))sel_registerName)((const char*)lparg0);

The compiler sees no cast of a SEL value at all — the function is declared (via its retyped pointer) as returning jlong directly. This is semantically safe on all 64-bit Apple platforms where SEL (an 8-byte opaque pointer) and jlong share the same size and representation.

This approach is driven entirely by two JNI generator annotations in OS.java, keeping the implementation inside the auto-generated os.c:

/**
 * @method flags=cast
 * @param selectorName cast=(const char*)
 */
public static final native long sel_registerName(String selectorName);

• flags=cast — instructs the generator to emit a function-pointer cast rather than a direct call
• cast=(const char*) — matches the native C parameter type const char* in the cast signature

Changes

• OS.java: adds @method flags=cast and @param selectorName cast=(const char*) annotations to sel_registerName
• os.c: updated generated function body (reflects what the generator produces from the new annotations)

Test plan

• Build natives from the binaries/org.eclipse.swt.cocoa.macosx.aarch64 fragment using mvn clean process-resources -Dnative=cocoa.macosx.aarch64 — confirms the -Wcast-of-sel-type warning is gone
• Verify the 7 remaining warnings are only the other known deprecated APIs from issue Replace deprecated native methods in macOS implementation #3186:
  • os.c:1102: CFURLCreateFromFSRef — deprecated macOS 10.9
  • os.c:1920: GetCurrentProcess — deprecated macOS 10.9
  • os.c:2119: LSGetApplicationForInfo — deprecated macOS 10.10
  • os.c:4040: NSPrintSavePath — deprecated macOS 10.6
  • os.c:4678: SecPolicySearchCopyNext — deprecated macOS 10.7
  • os.c:4694: SecPolicySearchCreate — deprecated macOS 10.7
  • os.c:4883: passing arguments to a function without a prototype [-Wdeprecated-non-prototype]
• Run the SWT test suite on macOS to confirm selector dispatch still works correctly across the codebase

Notes

This change was developed with the assistance of Claude Code (claude-sonnet-4-6). Multiple solution approaches were explored interactively, including direct casts, sel_getName routing, no_gen + os_custom.c, and the final function-pointer cast pattern.

Contributes to #3186.

[github-actions]

Test Results (macos)

   54 files  ±0     54 suites  ±0   5m 37s ⏱️ - 3m 38s
4 531 tests ±0  4 287 ✅ ±0  244 💤 ±0  0 ❌ ±0 
2 130 runs  ±0  2 068 ✅ ±0   62 💤 ±0  0 ❌ ±0 

Results for commit e5dc93d. ± Comparison against base commit d820f7e.