Fix crashes & ABI drift to build on current Swift#74
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A conformance's class will be nil when the conformance refers to a class that is only present in a newer SDK. For example, SDKAdImpression is only available on iOS 14.5. An app that uses SDKAdImpression would wrap it in `if @available` guards. While the conformance and class name is still present in the binary when it runs on iOS < 14.5, the class will be `nil`.
Make some Swift functions public so that the linker can see them when linking CEcho.
If they're not public, release builds would fail with undefined symbols errors:
Undefined symbols for architecture arm64:
"_lookupSection", referenced from:
__loadImageFunc in CEcho.o
"_registerProtocolConformances", referenced from:
__loadImageFunc in CEcho.o
"_registerProtocols", referenced from:
__loadImageFunc in CEcho.o
"_registerTypeMetadata", referenced from:
__loadImageFunc in CEcho.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The .indirectTypeDescriptor case loaded the GOT slot as a non-optional UnsafeRawPointer, which traps when the slot holds null (e.g. a type that was weak-linked from a newer SDK and isn't present at runtime). Load it as an optional and return nil instead of crashing, matching how the .directObjCClass case already guards weak-linked classes.
Each __swift5_types entry is a RelativeDirectPointerIntPair<ContextDescriptor, TypeReferenceKind>, packing the reference kind into the low 2 bits of the relative offset. registerTypeMetadata treated every entry as a plain direct relative pointer, so indirect type-descriptor records (emitted for cross-module type references, e.g. when Foundation is imported) produced a misaligned pointer and crashed getContextDescriptor with "load from misaligned raw pointer". Mask off the kind bits and dereference the GOT slot for indirect records, matching ConformanceDescriptor's type-reference handling.
- classAddressPoint/classSize grew by one word in newer Swift's class metadata header; Echo reads them correctly (its _ClassMetadata layout matches TargetClassMetadata, and instanceSize/fieldOffsets still match), so update the stale constants (16->24, 120->128, 136->144). - Drop the NSObject classAddressPoint/instanceAddressPoint/alignmentMask assertions: reading Swift class-metadata fields off a pure Objective-C class inspects unrelated bytes (the old 32767 sentinel was meaningless). Keep the isSwiftClass == false invariant.
TypeContextDescriptorFlags.resilientSuperclassRefKind masked the 3-bit field at bit 9 (& 0xE00) but never shifted it down, so any non-direct kind produced a value like 0x200 that isn't a valid TypeReferenceKind raw value and trapped the force-unwrap. This crashes on any class with a resilient superclass referenced indirectly -- i.e. a cross-module resilient superclass such as a Foundation base class. Shift the masked field down by 9 (matching the sibling decode in RuntimeValues). Regression test reflects Boat3<String>: JSONEncoder, whose Foundation superclass is referenced indirectly; reading the kind trapped before.
The key-argument loop stored args[0].0 for every slot instead of args[i].0, so instantiating a generic type via the buffer path (4+ arguments, or 2-3 arguments with witness tables) wrote the first type argument into every position -- silent metadata corruption. Existing tests missed it because they instantiated with identical arguments (Double, Double), where storing args[0] repeatedly is accidentally correct. Regression test instantiates FooBaz2<Int, Double> with distinct, witness-table-bearing arguments, forcing the buffer path and asserting argument order is preserved.
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Important
Must merge before #75 and #76
Summary
Echo no longer builds and runs cleanly on current Swift toolchains. This first PR restores a green build and test suite by fixing the crashes and ABI drift that accumulated since the library was last updated — each with a regression test that fails on the prior code.
Changes
ConformanceDescriptor.contextDescriptor— a conformance whose type was weak-linked from a newer SDK now returnsnilinstead of trapping a non-optional load.__swift5_typesdecoding — each record is aRelativeDirectPointerIntPair<ContextDescriptor, TypeReferenceKind>; the low two bits (the reference kind) weren't masked off, so indirect records (emitted whenever Foundation is imported) produced a misaligned pointer and crashedgetContextDescriptorwith "load from misaligned raw pointer". This was aborting the entire test suite.resilientSuperclassRefKind— the 3-bit field at bit 9 was masked but never shifted down, so any class with a cross-module resilient superclass (e.g. a Foundation base class) trapped a force-unwrappednil.MetadataAccessFunctionbuffer —createMetadataAccessBufferstoredargs[0]into every key-argument slot instead ofargs[i], silently corrupting any buffer-path generic metadata instantiation.ClassMetadatatest expectations updated for the current class-metadata ABI (the metadata header grew by one word).Testing
swift testis green (23 tests) on Swift 6.1.2 / macOS. Every fix above has a dedicated regression test.