[lld] [lld-macho] Fix unchecked Error crash for thin archive missing child (PR #97169)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lld-macho

Author: Daniel Bertalan (BertalanD)

<details>
<summary>Changes</summary>

The repro file in #<!-- -->94716 contains a few thin archives without their member object files present. I couldn't figure out why this happened (issue in repro tarball generation?), but this caused an "unhandled Error" crash on `LLVM_ENABLE_ABI_BREAKING_CHECKS` builds.

---
Full diff: https://github.com/llvm/llvm-project/pull/97169.diff


1 Files Affected:

- (modified) lld/MachO/Driver.cpp (+6-1) 


``````````diff
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index 9dddabcf3680c..eb64e764100b2 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -349,7 +349,12 @@ static InputFile *addFile(StringRef path, LoadType loadType,
         Error e = Error::success();
         for (const object::Archive::Child &c : file->getArchive().children(e)) {
           Expected<MemoryBufferRef> mb = c.getMemoryBufferRef();
-          if (!mb || !hasObjCSection(*mb))
+          if (!mb) {
+            llvm::consumeError(mb.takeError());
+            continue;
+          }
+
+          if (!hasObjCSection(*mb))
             continue;
           if (Error e = file->fetch(c, "-ObjC"))
             error(toString(file) + ": -ObjC failed to load archive member: " +

``````````

</details>


https://github.com/llvm/llvm-project/pull/97169