It's used in `Parser::collect_tokens_trailing_token` to decide whether
to capture a trailing token. But the callers actually know whether to
capture a trailing token, so it's simpler for them to just pass in a
bool.
Also, the `TrailingToken::Gt` case was weird, because it didn't result
in a trailing token being captured. It could have been subsumed by the
`TrailingToken::MaybeComma` case, and it effectively is in the new code.
Some parser improvements
I was looking closely at attribute handling in the parser while debugging some issues relating to #124141, and found a few small improvements.
``@spastorino``
It only has two call sites, and it extremely similar to
`Parser::parse_expr_dot_or_call_with`, in both name and behaviour. The
only difference is the latter has an `attrs` argument and an
`ensure_sufficient_stack` call. We can pass in an empty `attrs` as
necessary, as is already done at some `parse_expr_dot_or_call_with` call
sites.
Make parse error suggestions verbose and fix spans
Go over all structured parser suggestions and make them verbose style.
When suggesting to add or remove delimiters, turn them into multiple suggestion parts.
Fix `DebugParser`.
I tried using this and it didn't work at all. `prev_token` is never eof, so the accumulator is always false, which means the `then_some` always returns `None`, which means `scan` always returns `None`, and `tokens` always ends up an empty vec. I'm not sure how this code was supposed to work.
(An aside: I find `Iterator::scan` to be a pretty wretched function, that produces code which is very hard to understand. Probably why this is just one of two uses of it in the entire compiler.)
This commit changes it to a simpler imperative style that produces a valid `tokens` vec.
r? `@workingjubilee`
Clear `inner_attr_ranges` regularly.
There's a comment saying we don't do it for performance reasons, but it doesn't actually affect performance.
The commit also tweaks the control flow, to make clearer that two code paths are mutually exclusive.
r? ````@petrochenkov````
It currently doesn't work at all. This commit changes it to a simpler
imperative style that produces a valid `tokens` vec.
(An aside: I find `Iterator::scan` to be a pretty wretched function,
that produces code which is very hard to understand. Probably why this
is just one of two uses of it in the entire compiler.)
That method is currently badly broken, and the test output reflects
this. The obtained tokens list is always empty, except in the case where
we go two `bump`s past the final token, whereupon it will produce as
many `Eof` tokens as asked for.
Fix `Parser::look_ahead`
`Parser::look_ahead` has a slow but simple general case, and a fast special case that is hit most of the time. But the special case is buggy and behaves differently to the general case. There are also no unit tests. This PR fixes all of this, resulting in a `Parser::look_ahead` that is equally fast, slightly simpler, more correct, and better tested.
r? `@davidtwco`
This new special case is simpler than the old special case because it
only is used when `dist == 1`. But that's still enough to cover ~98% of
cases. This results in equivalent performance to the old special case,
and identical behaviour as the general case.
The general case at the bottom of `look_ahead` is slow, because it
clones the token cursor. Above it there is a special case for
performance that is hit most of the time and avoids the cloning.
Unfortunately, its behaviour differs from the general case in two ways.
- When within a pair of delimiters, if you look any distance past the
closing delimiter you get the closing delimiter instead of what comes
after the closing delimiter.
- It uses `tree_cursor.look_ahead(dist - 1)` which totally confuses
tokens with token trees. This means that only the first token in a
token tree will be seen. E.g. in a sequence like `{ a }` the `a` and
`}` will be skipped over. Bad!
It's likely that these differences weren't noticed before now because
the use of `look_ahead` in the parser is limited to small distances and
relatively few contexts.
Removing the special case causes slowdowns up of to 2% on a range of
benchmarks. The next commit will add a new, correct special case to
regain that lost performance.
Go over all structured parser suggestions and make them verbose style.
When suggesting to add or remove delimiters, turn them into multiple suggestion parts.
The new condition is equivalent in practice, but it's much more obvious
that it would result in an empty range, because the condition lines up
with the contents of the iterator.
There's a comment saying we don't do it for performance reasons, but it
doesn't actually affect performance.
The commit also tweaks the control flow, to make clearer that two code
paths are mutually exclusive.
Currently the second element is a `Vec<(FlatToken, Spacing)>`. But the
vector always has zero or one elements, and the `FlatToken` is always
`FlatToken::AttrTarget` (which contains an `AttributesData`), and the
spacing is always `Alone`. So we can simplify it to
`Option<AttributesData>`.
An assertion in `to_attr_token_stream` can can also be removed, because
`new_tokens.len()` was always 0 or 1, which means than `range.len()`
is always greater than or equal to it, because `range.is_empty()` is
always false (as per the earlier assertion).
And update the comment. Clearly the return type of this function was
changed at some point in the past, but its name and comment weren't
updated to match.
The number of source code bytes can't exceed a `u32`'s range, so a token
position also can't. This reduces the size of `Parser` and
`LazyAttrTokenStreamImpl` by eight bytes each.
