This allows us to avoid synthesizing tokens in `prepend_attr`, since we
have the original tokens available.
We still need to synthesize tokens when expanding `cfg_attr`,
but this is an unavoidable consequence of the syntax of `cfg_attr` -
the user does not supply the `#` and `[]` tokens that a `cfg_attr`
expands to.
Instead of trying to collect tokens at each depth, we 'flatten' the
stream as we go allong, pushing open/close delimiters to our buffer
just like regular tokens. One capturing is complete, we reconstruct a
nested `TokenTree::Delimited` structure, producing a normal
`TokenStream`.
The reconstructed `TokenStream` is not created immediately - instead, it is
produced on-demand by a closure (wrapped in a new `LazyTokenStream` type). This
closure stores a clone of the original `TokenCursor`, plus a record of the
number of calls to `next()/next_desugared()`. This is sufficient to reconstruct
the tokenstream seen by the callback without storing any additional state. If
the tokenstream is never used (e.g. when a captured `macro_rules!` argument is
never passed to a proc macro), we never actually create a `TokenStream`.
This implementation has a number of advantages over the previous one:
* It is significantly simpler, with no edge cases around capturing the
start/end of a delimited group.
* It can be easily extended to allow replacing tokens an an arbitrary
'depth' by just using `Vec::splice` at the proper position. This is
important for PR #76130, which requires us to track information about
attributes along with tokens.
* The lazy approach to `TokenStream` construction allows us to easily
parse an AST struct, and then decide after the fact whether we need a
`TokenStream`. This will be useful when we start collecting tokens for
`Attribute` - we can discard the `LazyTokenStream` if the parsed
attribute doesn't need tokens (e.g. is a builtin attribute).
The performance impact seems to be neglibile (see
https://github.com/rust-lang/rust/pull/77250#issuecomment-703960604). There is a
small slowdown on a few benchmarks, but it only rises above 1% for incremental
builds, where it represents a larger fraction of the much smaller instruction
count. There a ~1% speedup on a few other incremental benchmarks - my guess is
that the speedups and slowdowns will usually cancel out in practice.
Remove unused code
Rustc has a builtin lint for detecting unused code inside a crate, but when an item is marked `pub`, the code, even if unused inside the entire workspace, is never marked as such. Therefore, I've built [warnalyzer](https://github.com/est31/warnalyzer) to detect unused items in a cross-crate setting.
Closes https://github.com/est31/warnalyzer/issues/2
Fixes#74616
Makes progress towards #43081
Unblocks PR #76130
When pretty-printing an AST node, we may insert additional parenthesis
to ensure that precedence is properly preserved in code we output.
However, the proc macro implementation relies on comparing a
pretty-printed AST node to the captured `TokenStream`. Inserting extra
parenthesis changes the structure of the reparsed `TokenStream`, making
the comparison fail.
This PR refactors the AST pretty-printing code to allow skipping the
insertion of additional parenthesis. Several freestanding methods are
moved to trait methods on `PrintState`, which keep track of an internal
`insert_extra_parens` flag. This flag is normally `true`, but we expose
a public method which allows pretty-printing a nonterminal with
`insert_extra_parens = false`.
To avoid changing the public interface of `rustc_ast_pretty`, the
freestanding `_to_string` methods are changed to delegate to a
newly-crated `State`. The main pretty-printing code is moved to a new
`state` module to ensure that it does not accidentally call any of these
public helper functions (instead, the internal functions with the same
name should be used).
Makes progress towards #43081
In PR #73084, we started recursively expanded nonterminals during the
pretty-print/reparse check, allowing them to be properly compared
against the reparsed tokenstream.
Unfortunately, the recursive logic in that PR only handles the case
where a nonterminal appears inside a `TokenTree::Delimited`. If a
nonterminal appears directly in the expanded tokens of another
nonterminal, the inner nonterminal will not be expanded.
This PR fixes the recursive expansion of nonterminals, ensuring that
they are expanded wherever they occur.
If the right-hand iterator has exactly one more element than the
left-hand iterator, then both iterators will be fully consumed, but
the extra element will never be compared.
Ignore `|` and `+` tokens during proc-macro pretty-print check
Fixes#76182
This is an alternative to PR #76188
These tokens are not preserved in the AST in certain cases
(e.g. a leading `|` in a pattern or a trailing `+` in a trait bound).
This PR ignores them entirely during the pretty-print/reparse check
to avoid spuriously using the re-parsed tokenstream.
We currently only attach tokens when parsing a `:stmt` matcher for a
`macro_rules!` macro. Proc-macro attributes on statements are still
unstable, and need additional work.
Fixes#76182
This is an alternative to PR #76188
These tokens are not preserved in the AST in certain cases
(e.g. a leading `|` in a pattern or a trailing `+` in a trait bound).
This PR ignores them entirely during the pretty-print/reparse check
to avoid spuriously using the re-parsed tokenstream.
