C++20 templated lambdas not yet supported

[Swatinem]

I cam across the following identifiers:

_ZNSt6__ndk110__function6__funcIZN10xxxxxxxxxx20xxxxxxxxxxxxxxxxxxxx11xxxxxxxxxxxIN8xxxxxxxx14xxxxxxxxxxxxxxINS6_INS6_INS5_10xxxxxxxxxxEN14xxxxxxxxxxxxxx23xxxxxxxxxxxxxxxxxxxxxxxEEENS8_21xxxxxxxxxxxxxxxxxxxxxI18xxxxxxxxxxxxxxxxxxEEEE15xxxxxxxxxxxxxxxEESF_EEvRNS5_20xxxxxxxxxxxxxxxxxxxxIT_T0_EENS_8functionIFRS3_PSJ_EEEEUlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev

_ZNKSt6__ndk110__function6__funcIZN8xxxxxxxx9xxxxxxxxxINS_10shared_ptrINS2_20xxxxxxxxxxxxxxxxxxxxINS2_10xxxxxxxxxxE15xxxxxxxxxxxxxxxEEEES7_bEEODaT_MT0_T1_PKcEUlTyTyRSB_RSC_E_NS_9allocatorISJ_EEFvRNS2_14xxxxxxxxxxxxxxINSM_IS6_S7_EEbEERKbEE7__cloneEPNS0_6__baseISS_EE

They correctly demangle using macos c++filt as:

std::__ndk1::__function::__func<void xxxxxxxxxx::xxxxxxxxxxxxxxxxxxxx::xxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>, xxxxxxxxxxxxxxx>(xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>, xxxxxxxxxxxxxxx>&, std::__ndk1::function<xxxxxxxxxx::xxxxxxxxxxxxxxxxxxxx& (xxxxxxxxxxxxxxx*)>)::'lambda'<typename $T>(xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>&, int), std::__ndk1::allocator<void xxxxxxxxxx::xxxxxxxxxxxxxxxxxxxx::xxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>, xxxxxxxxxxxxxxx>(xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>, xxxxxxxxxxxxxxx>&, std::__ndk1::function<xxxxxxxxxx::xxxxxxxxxxxxxxxxxxxx& (xxxxxxxxxxxxxxx*)>)::'lambda'<typename $T>(xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>&, int)>, void (xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxxxx>, xxxxxxxxxxxxxx::xxxxxxxxxxxxxxxxxxxxx<xxxxxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx>, xxxxxxxxxxxxxxx>, int>&, int const&)>::~__func()

std::__ndk1::__function::__func<auto&& xxxxxxxx::xxxxxxxxx<std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx, bool>(std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >, bool xxxxxxxxxxxxxxx::*, char const*)::'lambda'<typename $T, typename $T0>(std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >&, xxxxxxxxxxxxxxx&), std::__ndk1::allocator<auto&& xxxxxxxx::xxxxxxxxx<std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >, xxxxxxxxxxxxxxx, bool>(std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >, bool xxxxxxxxxxxxxxx::*, char const*)::'lambda'<typename $T, typename $T0>(std::__ndk1::shared_ptr<xxxxxxxx::xxxxxxxxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx> >&, xxxxxxxxxxxxxxx&)>, void (xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx>, bool>&, bool const&)>::__clone(std::__ndk1::__function::__base<void (xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxxxxxx<xxxxxxxx::xxxxxxxxxx, xxxxxxxxxxxxxxx>, bool>&, bool const&)>*) const

So both have a …'lambda'<typename $T… in them, which is encoded as …UlTY….

I would like to work on this, still trying to figure out how all this fits together.
Since all the productions have bnf-like comments, is there a reference for all this somewhere? I didn’t really find anything.

From reading the code, I guess this has to go somewhere in the ClosureTypeName parser?

cpp_demangle/src/ast.rs

Lines 6909 to 6936 in 1e51bce

	/// The `<closure-type-name>` production.
	///
	/// ```text
	/// <closure-type-name> ::= Ul <lambda-sig> E [ <nonnegative number> ] _
	/// ```
	#[derive(Clone, Debug, PartialEq, Eq)]
	pub struct ClosureTypeName(LambdaSig, Option<usize>);
	impl Parse for ClosureTypeName {
	fn parse<'a, 'b>(
	ctx: &'a ParseContext,
	subs: &'a mut SubstitutionTable,
	input: IndexStr<'b>,
	) -> Result<(ClosureTypeName, IndexStr<'b>)> {
	try_begin_parse!("ClosureTypeName", ctx, input);
	let tail = consume(b"Ul", input)?;
	let (sig, tail) = LambdaSig::parse(ctx, subs, tail)?;
	let tail = consume(b"E", tail)?;
	let (num, tail) = if let Ok((num, tail)) = parse_number(10, false, tail) {
	(Some(num as _), tail)
	} else {
	(None, tail)
	};
	let tail = consume(b"_", tail)?;
	Ok((ClosureTypeName(sig, num), tail))
	}
	}

[khuey]

The BNF is generally taken from libiberty. The actual cxx abi spec on Github doesn't seem to be updated in a timely fashion.

If you're trying to figure out why a symbol doesn't parse, it helps to build with the logging feature. Then you'll get output like this

                                                (Name "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev                                                             [532/1855]
"
                                                    (NestedName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                    )
                                                    (UnscopedName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                        (UnqualifiedName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                            (OperatorName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                (SimpleOperatorName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                )
                                                            )
                                                            (CtorDtorName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                            )
                                                            (SourceName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                            )
                                                            (TaggedName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                            )
                                                            (ClosureTypeName "UlTyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                (LambdaSig "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                    (TypeHandle "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                        (BuiltinType "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                            (StandardBuiltinType "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                            )
                                                                        )
                                                                        (ClassEnumType "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                            (Name "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                                (NestedName "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                                )
                                                                                (UnscopedName "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                                    (UnqualifiedName "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev
"
                                                                                        (OperatorName "TyRSI_iE_NS_9allocatorISS_EEFvRNS6_INS6_ISG_SF_EEiEERKiEED0Ev

If you look at this log you'll see that we're recognizing "Ul" as a lambda signature, but we eventually get hung up on the "Ty" that follows it. binutils c++filter doesn't seem to understand this construct either, so I'd look at llvm's demangler to see what "Ty" is supposed to be to start with.