8000 [lldb] Avoid mangling empty opaque types by kastiglione · Pull Request #10947 · swiftlang/llvm-project · GitHub
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[lldb] Avoid mangling empty opaque types #10947

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[lldb] Avoid mangling empty opaque types #10947

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@kastiglione kastiglione commented Jul 2, 2025 •
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Update TypeSystemSwiftTypeRef::RemangleAsType to handle empty opaque types. Without this change, assertions will occur when running unit tests with an asserts-build of lldb.

An example of where this happens is Builtin.RawPointer ($sBpD). For values with that type, the typeref is:

(swift::reflection::OpaqueTypeRef *) typeref = 0x000060000309c000 {
  swift::reflection::TypeRef = {
    Kind = Opaque
  }
}

When demangling the above typeref, the resulting demangle tree is an empty OpaqueType:

(swift::Demangle::NodePointer) node = 0x0000000105240420 Type, 1 child {
  NodeKind = Type
  [0] = 0x0000000105240408 OpaqueType, 0 children {
    NodeKind = OpaqueType
  }
}

In Swift's Remangler::mangleOpaqueType, it's expected that the opaque type have 3 children:

DEMANGLER_ASSERT(node->getNumChildren() >= 3, node);

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@kastiglione kastiglione marked this pull request as ready for review July 2, 2025 22:16
@kastiglione kastiglione requested a review from a team as a code owner July 2, 2025 22:16
@kastiglione kastiglione requested a review from adrian-prantl July 2, 2025 22:17
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kastiglione commented Jul 2, 2025 •
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A possible alternative to this is to update Remangler::mangleOpaqueType to accept opaque nodes with no children, but I'm not sure whether that's a valid change to make, or not.

@kastiglione kastiglione mentioned this pull request Jul 2, 2025
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This patch seems fine for avoiding the crash, but: Is there a bug in the remangler that makes it impossible to round-trip $sBpD? If yes, would it be better to fix that instead?

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@adrian-prantl adrian-prantl Awaiting requested review from adrian-prantl

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