NullPropagationTransform only rewrites "x != null ? x.Chain : fallback"
into "x?.Chain ?? fallback" when the chain's inferred type is a
non-nullable value type, and InferType had no case for ldlen. Array length
therefore came back as UnknownType, so "arr?.Length ?? 0" was left as a
ternary.
The inferred type mirrors ExpressionBuilder.VisitLdLen, which decides
between Array.Length and Array.LongLength from the result type alone.
Found while investigating #3704, where the surviving ternary also keeps the
tested array in a stack slot and strands the typeof of a dynamic call's
static target. That issue is fixed separately in #4072, whose DynamicTests
cases pinned the ternary as expected output; those blocks round-trip
exactly now, so they are gone.
Also carries a review follow-up that missed #4072: the static-target test
in VisitDynamicInvokeMemberInstruction is a plain null check, the way
DynamicInvokeMemberInstruction itself tests the field, rather than a
pattern match binding a name it does not need.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Shortening default(T) is the same problem as removing the redundant cast
around a lambda whose delegate type the context already fixes, so it uses
the same mechanism: ConvertTo makes the explicit type implicit when the
conversion is an identity conversion and the caller allows an implicit
one. The literal keeps the type it was shortened from, so any later
conversion to a different type - or any context that requires an explicit
type, such as an overload resolution recheck falling back to CastArguments
- can spell default(T) out again. That keeps the value intact where the
bare literal would change it, e.g. "object o = default(SomeStruct)", which
boxes a non-null struct while "default" would be null.
Because the shortened literal resolves to DefaultLiteralResolveResult,
CallBuilder's existing overload resolution recheck sees a real default
literal and rejects ambiguous calls on its own; no separate bookkeeping
about which arguments may stay untyped is needed. Only the contexts that
supply no target type at all restore the explicit form: an awaited
expression, and arguments of operator methods, which later become operator
or cast syntax rather than calls.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The currently implementation is somewhat minimal and only works in a very limited set of circumstances:
* the ref local is single-assignment
* the ref local is initialized directly with 'ldloca target; stloc ref_local',
not a derived pointer (e.g. 'ldloca target; ldflda F; stloc ref_local').
* all uses of the ref_local are immediately consuming the address
This improves variable splitting cases where the compiler re-uses a stack slot containing a reference,
e.g. in some cases of '?.' on Nullable<T>.
Siegfried Pammer
Christoph Wille
Peter Crabtree
dotnet format
Daniel Grunwald