The C# 14 feature is pure source sugar: a lambda parameter may carry
ref/out/in/scoped/ref readonly without declaring a type, but the IL
always has fully-typed parameters, so the decompiler's explicitly-typed
output is the correct round-trip. LambdaParameterModifiers pins that
this round-trip works: custom delegate types with each modifier
(including scoped by-value, scoped ref, and mixed parameter lists),
block- and expression-bodied lambdas, captures alongside ref
parameters, generic ref delegates, lambda parameter attributes,
call-site modifiers (including 'in' for 'ref readonly' parameters),
unused-parameter anonymous methods, and a local-function contrast.
CS140-gated branches compile the untyped sugar (and attributed sugar)
under Roslyn latest to prove it produces the same decompilation.
ScopedLambdaParameters is Assert.Ignore'd: when an anonymous function's
'scoped ref' parameter is unused, the decompiler drops the parameter
list, losing the required 'scoped' modifier; the output then fails to
recompile with CS8986 because the implicit parameters of a
parameter-list-less anonymous method are unscoped. The fixture is the
desired output (parameter list retained); all four Roslyn 4.14/latest
debug/opt configs compile it and fail only at the output comparison.
Assisted-by: Claude:claude-fable-5:Claude Code
Siegfried Pammer