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libsyntax: introduce 'fn is_keyword_ahead(dist, keywords)'.#61321

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Merged
bors merged 1 commit into from
May 30, 2019
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libsyntax: introduce 'fn is_keyword_ahead(dist, keywords)'. #61321

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73 changes: 38 additions & 35 deletions src/libsyntax/parse/parser.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1087,6 +1087,11 @@ impl<'a> Parser<'a> {
}
}

/// Returns whether any of the given keywords are `dist` tokens ahead of the current one.
fn is_keyword_ahead(&self, dist: usize, kws: &[Symbol]) -> bool {

@CentrilCentrilMay 29, 2019

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We could possibly reduce this to just one keyword... that is one option... :)

@petrochenkovpetrochenkovMay 29, 2019

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18 single keyword vs 5 multiple keywords.
+ look_ahead is a single array lookup and a match, more or less, so not much reason to optimize.
Might be reasonable to reduce to one keyword.

self.look_ahead(dist, |t| kws.iter().any(|&kw| t.is_keyword(kw)))
}

/// Is the current token one of the keywords that signals a bare function type?
fn token_is_bare_fn_keyword(&mut self) -> bool {
self.check_keyword(kw::Fn) ||
Expand DownExpand Up@@ -4270,7 +4275,7 @@ impl<'a> Parser<'a> {
self.token.is_keyword(kw::Async) &&
(
( // `async move {`
self.look_ahead(1, |t| t.is_keyword(kw::Move)) &&
self.is_keyword_ahead(1, &[kw::Move]) &&
self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
) || ( // `async {`
self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
Expand All@@ -4280,12 +4285,12 @@ impl<'a> Parser<'a> {

fn is_async_fn(&self) -> bool {
self.token.is_keyword(kw::Async) &&
self.look_ahead(1, |t| t.is_keyword(kw::Fn))
self.is_keyword_ahead(1, &[kw::Fn])
}

fn is_do_catch_block(&self) -> bool {
self.token.is_keyword(kw::Do) &&
self.look_ahead(1, |t| t.is_keyword(kw::Catch)) &&
self.is_keyword_ahead(1, &[kw::Catch]) &&
self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
!self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
}
Expand All@@ -4309,17 +4314,17 @@ impl<'a> Parser<'a> {

fn is_existential_type_decl(&self) -> bool {
self.token.is_keyword(kw::Existential) &&
self.look_ahead(1, |t| t.is_keyword(kw::Type))
self.is_keyword_ahead(1, &[kw::Type])
}

fn is_auto_trait_item(&self) -> bool {
// auto trait
(self.token.is_keyword(kw::Auto)
&& self.look_ahead(1, |t| t.is_keyword(kw::Trait)))
(self.token.is_keyword(kw::Auto) &&
self.is_keyword_ahead(1, &[kw::Trait]))
|| // unsafe auto trait
(self.token.is_keyword(kw::Unsafe) &&
self.look_ahead(1, |t| t.is_keyword(kw::Auto)) &&
self.look_ahead(2, |t| t.is_keyword(kw::Trait)))
self.is_keyword_ahead(1, &[kw::Auto]) &&
self.is_keyword_ahead(2, &[kw::Trait]))
}

fn eat_macro_def(&mut self, attrs: &[Attribute], vis: &Visibility, lo: Span)
Expand DownExpand Up@@ -5486,7 +5491,7 @@ impl<'a> Parser<'a> {
(if isolated_self(self, 1) {
self.bump();
SelfKind::Region(None, Mutability::Immutable)
} else if self.look_ahead(1, |t| t.is_keyword(kw::Mut)) &&
} else if self.is_keyword_ahead(1, &[kw::Mut]) &&
isolated_self(self, 2) {
self.bump();
self.bump();
Expand All@@ -5497,7 +5502,7 @@ impl<'a> Parser<'a> {
let lt = self.expect_lifetime();
SelfKind::Region(Some(lt), Mutability::Immutable)
} else if self.look_ahead(1, |t| t.is_lifetime()) &&
self.look_ahead(2, |t| t.is_keyword(kw::Mut)) &&
self.is_keyword_ahead(2, &[kw::Mut]) &&
isolated_self(self, 3) {
self.bump();
let lt = self.expect_lifetime();
Expand DownExpand Up@@ -5676,8 +5681,7 @@ impl<'a> Parser<'a> {
/// (returns `false` for things like `const fn`, etc.).
fn is_const_item(&self) -> bool {
self.token.is_keyword(kw::Const) &&
!self.look_ahead(1, |t| t.is_keyword(kw::Fn)) &&
!self.look_ahead(1, |t| t.is_keyword(kw::Unsafe))
!self.is_keyword_ahead(1, &[kw::Fn, kw::Unsafe])
}

/// Parses all the "front matter" for a `fn` declaration, up to
Expand DownExpand Up@@ -5955,7 +5959,7 @@ impl<'a> Parser<'a> {
self.look_ahead(1, |t| t.is_lifetime() || t.is_ident()) &&
self.look_ahead(2, |t| t == &token::Gt || t == &token::Comma ||
t == &token::Colon || t == &token::Eq) ||
self.look_ahead(1, |t| t.is_keyword(kw::Const)))
self.is_keyword_ahead(1, &[kw::Const]))
}

fn parse_impl_body(&mut self) -> PResult<'a, (Vec<ImplItem>, Vec<Attribute>)> {
Expand DownExpand Up@@ -6316,7 +6320,7 @@ impl<'a> Parser<'a> {
// `()` or a tuple might be allowed. For example, `struct Struct(pub (), pub (usize));`.
// Because of this, we only `bump` the `(` if we're assured it is appropriate to do so
// by the following tokens.
if self.look_ahead(1, |t| t.is_keyword(kw::Crate)) &&
if self.is_keyword_ahead(1, &[kw::Crate]) &&
self.look_ahead(2, |t| t != &token::ModSep) // account for `pub(crate::foo)`
{
// `pub(crate)`
Expand All@@ -6328,7 +6332,7 @@ impl<'a> Parser<'a> {
VisibilityKind::Crate(CrateSugar::PubCrate),
);
return Ok(vis)
} else if self.look_ahead(1, |t| t.is_keyword(kw::In)) {
} else if self.is_keyword_ahead(1, &[kw::In]) {
// `pub(in path)`
self.bump(); // `(`
self.bump(); // `in`
Expand All@@ -6340,8 +6344,7 @@ impl<'a> Parser<'a> {
});
return Ok(vis)
} else if self.look_ahead(2, |t| t == &token::CloseDelim(token::Paren)) &&
self.look_ahead(1, |t| t.is_keyword(kw::Super) ||
t.is_keyword(kw::SelfLower))
self.is_keyword_ahead(1, &[kw::Super, kw::SelfLower])
{
// `pub(self)` or `pub(super)`
self.bump(); // `(`
Expand DownExpand Up@@ -6380,13 +6383,16 @@ impl<'a> Parser<'a> {
fn parse_defaultness(&mut self) -> Defaultness {
// `pub` is included for better error messages
if self.check_keyword(kw::Default) &&
self.look_ahead(1, |t| t.is_keyword(kw::Impl) ||
t.is_keyword(kw::Const) ||
t.is_keyword(kw::Fn) ||
t.is_keyword(kw::Unsafe) ||
t.is_keyword(kw::Extern) ||
t.is_keyword(kw::Type) ||
t.is_keyword(kw::Pub)) {
self.is_keyword_ahead(1, &[
kw::Impl,
kw::Const,
kw::Fn,
kw::Unsafe,
kw::Extern,
kw::Type,
kw::Pub,
])
{
self.bump(); // `default`
Defaultness::Default
} else {
Expand DownExpand Up@@ -6880,7 +6886,7 @@ impl<'a> Parser<'a> {
// Ident ["<"...">"] ["where" ...] ("=" | ":") Ty ";"
if self.check_keyword(kw::Type) ||
self.check_keyword(kw::Existential) &&
self.look_ahead(1, |t| t.is_keyword(kw::Type)) {
self.is_keyword_ahead(1, &[kw::Type]) {
let existential = self.eat_keyword(kw::Existential);
assert!(self.eat_keyword(kw::Type));
Some(self.parse_existential_or_alias(existential))
Expand DownExpand Up@@ -7157,7 +7163,7 @@ impl<'a> Parser<'a> {
let const_span = self.prev_span;
if self.check_keyword(kw::Fn)
|| (self.check_keyword(kw::Unsafe)
&& self.look_ahead(1, |t| t.is_keyword(kw::Fn))) {
&& self.is_keyword_ahead(1, &[kw::Fn])) {
// CONST FUNCTION ITEM
let unsafety = self.parse_unsafety();
self.bump();
Expand DownExpand Up@@ -7202,10 +7208,10 @@ impl<'a> Parser<'a> {
// `unsafe async fn` or `async fn`
if (
self.check_keyword(kw::Unsafe) &&
self.look_ahead(1, |t| t.is_keyword(kw::Async))
self.is_keyword_ahead(1, &[kw::Async])
) || (
self.check_keyword(kw::Async) &&
self.look_ahead(1, |t| t.is_keyword(kw::Fn))
self.is_keyword_ahead(1, &[kw::Fn])
)
{
// ASYNC FUNCTION ITEM
Expand DownExpand Up@@ -7239,8 +7245,7 @@ impl<'a> Parser<'a> {
return Ok(Some(item));
}
if self.check_keyword(kw::Unsafe) &&
(self.look_ahead(1, |t| t.is_keyword(kw::Trait)) ||
self.look_ahead(1, |t| t.is_keyword(kw::Auto)))
self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
{
// UNSAFE TRAIT ITEM
self.bump(); // `unsafe`
Expand All@@ -7263,11 +7268,9 @@ impl<'a> Parser<'a> {
}
if self.check_keyword(kw::Impl) ||
self.check_keyword(kw::Unsafe) &&
self.look_ahead(1, |t| t.is_keyword(kw::Impl)) ||
self.check_keyword(kw::Default) &&
self.look_ahead(1, |t| t.is_keyword(kw::Impl)) ||

@oli-obkoli-obkMay 29, 2019

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side-note (pre existing): default unsafe fn is eaten by this if and will error?

@CentrilCentrilMay 29, 2019

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Yeah I believe so.

self.is_keyword_ahead(1, &[kw::Impl]) ||
self.check_keyword(kw::Default) &&
self.look_ahead(1, |t| t.is_keyword(kw::Unsafe)) {
self.is_keyword_ahead(1, &[kw::Impl, kw::Unsafe]) {
// IMPL ITEM
let defaultness = self.parse_defaultness();
let unsafety = self.parse_unsafety();
Expand DownExpand Up@@ -7360,7 +7363,7 @@ impl<'a> Parser<'a> {
}
if self.check_keyword(kw::Trait)
|| (self.check_keyword(kw::Auto)
&& self.look_ahead(1, |t| t.is_keyword(kw::Trait)))
&& self.is_keyword_ahead(1, &[kw::Trait]))
{
let is_auto = if self.eat_keyword(kw::Trait) {
IsAuto::No
Expand Down