The descriptor map is keyed by a simplified mangling that canonicalizes the differences that we accept in _contextDescriptorMatchesMangling, such as the ability to specify any kind of type with an OtherNominalType node.
This simplified mangling is not necessarily unique, but we use _contextDescriptorMatchesMangling for the final equality checking when looking up entries in the map, so occasional collisions are acceptable and get resolved when probing the table.
The table is meant to be comprehensive, so it includes all descriptors that can be looked up by name, and a negative result means the descriptor does not exist in the shared cache. We add a flag to the options that can mark it as non-definitive in case we ever need to degrade this, and fall back to a full search after a negative result.
The map encompasses the entire shared cache but we need to reject lookups for types in images that aren't loaded. The map includes an image index which allows us to cheaply query whether a given descriptor is in a loaded image or not, so we can ignore ones which are not.
TypeMetadataPrivateState now has a separate sections array for sections within the shared cache. _searchTypeMetadataRecords consults the map first. If no result is found in the map and the map is marked as comprehensive, then only the sections outside the shared cache need to be scanned.
Replace the SWIFT_DEBUG_ENABLE_LIB_PRESPECIALIZED environment variable with one specifically for metadata and one for descriptor lookup so they can be controlled independently. Also add SWIFT_DEBUG_VALIDATE_LIB_PRESPECIALIZED_DESCRIPTOR_LOOKUP which consults the map and does the full scan, and ensures they produce the same result, for debugging purposes.
Enhance the environment variable code to track whether a variable was set at all. This allows SWIFT_DEBUG_ENABLE_LIB_PRESPECIALIZED to override the default in either direction.
Remove the disablePrespecializedMetadata global and instead modify the mapConfiguration to disable prespecialized metadata when an image is loaded that overrides one in the shared cache.
rdar://113059233
Don't use strcmp to compare the candidate key with the search key, as the search key may not be NUL terminated. Use strncmp and a length check on the candidate key.
This library uses GenericMetadataBuilder with a ReaderWriter that can read data and resolve pointers from MachO files, and emit a JSON representation of a dylib containing the built metadata.
We use LLVM's binary file readers to parse the MachO files and resolve fixups so we can follow pointers. This code is somewhat MachO specific, but could be generalized to other formats that LLVM supports.
rdar://116592577
