Three places decided independently whether a backing field would still be
declared, and they disagreed. ReplaceBackingFieldUsage rewrote a constructor
store into a property assignment whenever the property looked collapsible,
without asking whether PatternStatementTransform would actually remove the
declaration; ConvertField printed the "field" keyword on the FieldKeyword
setting alone, ignoring the GetterOnlyAutomaticProperties veto that
MemberIsHidden applies to the same field.
Two consequences, both silent. A setter-less property under
GetterOnlyAutomaticProperties = false kept its declaration and got "field" in
the getter anyway, so the keyword bound to a second synthesized field and the
declared one went unwritten. A settable property under AutomaticProperties =
false had its initializing store turned into a property assignment that
TransformFieldAndConstructorInitializers could no longer lift, leaving the
constructor in the output with an unconverted base-constructor call.
BackingFieldWillBeRemoved is now the single verdict every branch consults, and
it mirrors the transform's own entry gate. A property that keeps explicit
accessors is no longer addressed by name: the store stays a field reference and
becomes the property initializer, which is what field-backed storage means. The
one exception is a setter-less property's constructor store, which C# allows to
be written as an assignment and which has no other expressible form.
IsBackingFieldOfAutomaticProperty now answers through TryGetBackingField instead
of its own name check, so the two directions of "is this field that property's
storage" cannot diverge on staticness or field type. ReplaceBackingFieldUsage
dispatches on the resolve result rather than the identifier's spelling; after
ConvertField the same field appears both as "field" and under its metadata name
carrying the same annotation, so matching the name was matching the wrong thing.
The keyword's own precondition moves into a CanUseFieldKeyword local function.
Seven clauses with comment blocks wedged between them had to be read as one
expression; as one early return per rule the list reads in order.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Siegfried Pammer