The speculative insertion of StubReferences after elements in an
argument list turned out to not be necessary, because we decided we want
to insert per-argument initialization steps after all arguments are
evaluated, rather than interleaving them. The StubReferences we insert
are causing some minor code complexity, so remove them.
We still create StubReferences when performing patch-ups of
already-emitted code, but we no longer ever need to look through them
when determining whether an initializer was a literal or when evaluating
a type expression.
This implements initializing expression semantics for structs and
tuples, following #2006 and discussions since.
Tuple and (and analogously, struct) literals are treated as having a
mixed expression category that is later resolved based on how the
literal is used, as either a tuple initializer or a tuple value, at
which point we create a `TupleInit` or `TupleValue` that represents the
formation of the tuple initializer or tuple value from the tuple
literal.
There's quite a lot of TODOs here, and the SemIR representation is still
not quite right, but this seems like a good place to checkpoint some
incremental progress.
- `Peek()` no longer returns a useful value, because we often don't
allocate a `NodeBlockId` until we finish building the block. Remove it
and update both its callers.
- Rename `PeekForAdd()` to `PeekOrAdd()` since it's no longer used to
get a block ID to add elements into.
- `PushForAdd()` was unused. Remove it.
- Add `NodeBlockStack::AddNode` to combine the operations of adding a
node and inserting it into a block.
This better reflects the purpose of these semantics nodes, and prepares
for adding TupleValue and TupleInit nodes to represent forming values
and initializers from literals.
Continuing along with #3070. Note this is just a file rename, with BUILD
edits; every file previously in semantics/ should show as moved (except
maybe BUILDs, which split).
Richard Smith
Jon Ross-Perkins