Demangler: Save state to allow reentrant demangling. #25856
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If somebody called `demangleType` or `demangleSymbol` using a demangler that was already in the middle of demangling a string, then the state for the new demangler would clobber the old demangler. This manifested in rdar://problem/50380275 because, as part of demangling a string with a symbolic reference to a private type's context, we would demangle the debug string for the referenced context using the same demangler. If there were additional operators in the original string after the symbolic reference, these never got demangled because the demangler was now in the state of having completed demangling the other string, so we would drop nesting, and incorrectly report field types of, for instance, `Array<PrivateStruct>` or `(PrivateStruct, OtherStruct)` as just being `PrivateStruct`. This is a likely situation to be in, especially now that `Demangler` objects also serve as arena allocators for their demangled nodes, so change the top-level demangler entry points to use an RAII object to push and pop the existing state instead of unilaterally clobbering the existing state.
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If somebody called
demangleTypeordemangleSymbolusing a demangler that was alreadyin the middle of demangling a string, then the state for the new demangler would clobber the old
demangler. This manifested in rdar://problem/50380275 and rdar://problem/52349591 because, as part of demangling a
string with a symbolic reference to a private type's context, we would demangle the debug string
for the referenced context using the same demangler. If there were additional operators in the
original string after the symbolic reference, these never got demangled because the demangler
was now in the state of having completed demangling the other string, so we would drop nesting,
and incorrectly report field types of, for instance,
Array<PrivateStruct>or(PrivateStruct, OtherStruct)as just beingPrivateStruct.This is a likely situation to be in, especially now that
Demanglerobjects also serve asarena allocators for their demangled nodes, so change the top-level demangler entry points
to use an RAII object to push and pop the existing state instead of unilaterally clobbering
the existing state.