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Improve parsing diagnostic for negative supertrait bounds #57364

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Feb 24, 2019
Merged

Improve parsing diagnostic for negative supertrait bounds #57364

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80 changes: 59 additions & 21 deletions src/libsyntax/parse/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1731,7 +1731,7 @@ impl<'a> Parser<'a> {
}
} else if self.eat_keyword(keywords::Impl) {
// Always parse bounds greedily for better error recovery.
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
} else if self.check_keyword(keywords::Dyn) &&
Expand All @@ -1740,13 +1740,13 @@ impl<'a> Parser<'a> {
!can_continue_type_after_non_fn_ident(t))) {
self.bump(); // `dyn`
// Always parse bounds greedily for better error recovery.
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
} else if self.check(&token::Question) ||
self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
// Bound list (trait object type)
TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus)?,
TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
TraitObjectSyntax::None)
} else if self.eat_lt() {
// Qualified path
Expand Down Expand Up @@ -1792,7 +1792,7 @@ impl<'a> Parser<'a> {
let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
if parse_plus {
self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
bounds.append(&mut self.parse_generic_bounds()?);
bounds.append(&mut self.parse_generic_bounds(None)?);
}
Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
}
Expand All @@ -1817,7 +1817,7 @@ impl<'a> Parser<'a> {
}

self.bump(); // `+`
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
let sum_span = ty.span.to(self.prev_span);

let mut err = struct_span_err!(self.sess.span_diagnostic, sum_span, E0178,
Expand Down Expand Up @@ -5492,18 +5492,24 @@ impl<'a> Parser<'a> {
/// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
/// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
/// ```
fn parse_generic_bounds_common(&mut self, allow_plus: bool) -> PResult<'a, GenericBounds> {
fn parse_generic_bounds_common(&mut self,
allow_plus: bool,
colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
let mut bounds = Vec::new();
let mut negative_bounds = Vec::new();
let mut last_plus_span = None;
loop {
// This needs to be synchronized with `Token::can_begin_bound`.
let is_bound_start = self.check_path() || self.check_lifetime() ||
self.check(&token::Not) || // used for error reporting only
self.check(&token::Question) ||
self.check_keyword(keywords::For) ||
self.check(&token::OpenDelim(token::Paren));
if is_bound_start {
let lo = self.span;
let has_parens = self.eat(&token::OpenDelim(token::Paren));
let inner_lo = self.span;
let is_negative = self.eat(&token::Not);
let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
if self.token.is_lifetime() {
if let Some(question_span) = question {
Expand Down Expand Up @@ -5534,28 +5540,60 @@ impl<'a> Parser<'a> {
if has_parens {
self.expect(&token::CloseDelim(token::Paren))?;
}
let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_span));
let modifier = if question.is_some() {
TraitBoundModifier::Maybe
let poly_span = lo.to(self.prev_span);
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if is_negative {
negative_bounds.push(
last_plus_span.or(colon_span).unwrap()
.to(poly_span));
} else {
TraitBoundModifier::None
};
bounds.push(GenericBound::Trait(poly_trait, modifier));
let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
let modifier = if question.is_some() {
TraitBoundModifier::Maybe
} else {
TraitBoundModifier::None
};
bounds.push(GenericBound::Trait(poly_trait, modifier));
}
}
} else {
break
}

if !allow_plus || !self.eat_plus() {
break
}
} else {
last_plus_span = Some(self.prev_span);
}
}

if !negative_bounds.is_empty() {
let plural = negative_bounds.len() > 1;
let mut err = self.struct_span_err(negative_bounds,
"negative trait bounds are not supported");
let bound_list = colon_span.unwrap().to(self.prev_span);
let mut new_bound_list = String::new();
if !bounds.is_empty() {
let mut snippets = bounds.iter().map(|bound| bound.span())
.map(|span| self.sess.source_map().span_to_snippet(span));
while let Some(Ok(snippet)) = snippets.next() {
new_bound_list.push_str(" + ");
new_bound_list.push_str(&snippet);
}
new_bound_list = new_bound_list.replacen(" +", ":", 1);
}
err.span_suggestion_short(bound_list,
&format!("remove the trait bound{}",
if plural { "s" } else { "" }),
new_bound_list,
Applicability::MachineApplicable);
err.emit();
}

return Ok(bounds);
}

fn parse_generic_bounds(&mut self) -> PResult<'a, GenericBounds> {
self.parse_generic_bounds_common(true)
fn parse_generic_bounds(&mut self, colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
self.parse_generic_bounds_common(true, colon_span)
}

/// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
Expand Down Expand Up @@ -5583,7 +5621,7 @@ impl<'a> Parser<'a> {

// Parse optional colon and param bounds.
let bounds = if self.eat(&token::Colon) {
self.parse_generic_bounds()?
self.parse_generic_bounds(None)?
} else {
Vec::new()
};
Expand Down Expand Up @@ -5615,7 +5653,7 @@ impl<'a> Parser<'a> {

// Parse optional colon and param bounds.
let bounds = if self.eat(&token::Colon) {
self.parse_generic_bounds()?
self.parse_generic_bounds(None)?
} else {
Vec::new()
};
Expand Down Expand Up @@ -6028,7 +6066,7 @@ impl<'a> Parser<'a> {
// or with mandatory equality sign and the second type.
let ty = self.parse_ty()?;
if self.eat(&token::Colon) {
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
where_clause.predicates.push(ast::WherePredicate::BoundPredicate(
ast::WhereBoundPredicate {
span: lo.to(self.prev_span),
Expand Down Expand Up @@ -6542,14 +6580,14 @@ impl<'a> Parser<'a> {

// Parse optional colon and supertrait bounds.
let bounds = if self.eat(&token::Colon) {
self.parse_generic_bounds()?
self.parse_generic_bounds(Some(self.prev_span))?
} else {
Vec::new()
};

if self.eat(&token::Eq) {
// it's a trait alias
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
tps.where_clause = self.parse_where_clause()?;
self.expect(&token::Semi)?;
if is_auto == IsAuto::Yes {
Expand Down Expand Up @@ -7584,7 +7622,7 @@ impl<'a> Parser<'a> {
tps.where_clause = self.parse_where_clause()?;
let alias = if existential {
self.expect(&token::Colon)?;
let bounds = self.parse_generic_bounds()?;
let bounds = self.parse_generic_bounds(None)?;
AliasKind::Existential(bounds)
} else {
self.expect(&token::Eq)?;
Expand Down
14 changes: 14 additions & 0 deletions src/test/ui/parser/issue-33418.fixed
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
// run-rustfix

trait Tr {} //~ ERROR negative trait bounds are not supported
trait Tr2: SuperA {} //~ ERROR negative trait bounds are not supported
trait Tr3: SuperB {} //~ ERROR negative trait bounds are not supported
trait Tr4: SuperB + SuperD {}
trait Tr5 {}

trait SuperA {}
trait SuperB {}
trait SuperC {}
trait SuperD {}

fn main() {}
16 changes: 16 additions & 0 deletions src/test/ui/parser/issue-33418.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
// run-rustfix

trait Tr: !SuperA {} //~ ERROR negative trait bounds are not supported
trait Tr2: SuperA + !SuperB {} //~ ERROR negative trait bounds are not supported
trait Tr3: !SuperA + SuperB {} //~ ERROR negative trait bounds are not supported
trait Tr4: !SuperA + SuperB //~ ERROR negative trait bounds are not supported
+ !SuperC + SuperD {}
trait Tr5: !SuperA //~ ERROR negative trait bounds are not supported
+ !SuperB {}

trait SuperA {}
trait SuperB {}
trait SuperC {}
trait SuperD {}

fn main() {}
42 changes: 42 additions & 0 deletions src/test/ui/parser/issue-33418.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
error: negative trait bounds are not supported
--> $DIR/issue-33418.rs:3:9
|
LL | trait Tr: !SuperA {} //~ ERROR negative trait bounds are not supported
| ^^^^^^^^^ help: remove the trait bound

error: negative trait bounds are not supported
--> $DIR/issue-33418.rs:4:19
|
LL | trait Tr2: SuperA + !SuperB {} //~ ERROR negative trait bounds are not supported
| ---------^^^^^^^^^
| |
| help: remove the trait bound

error: negative trait bounds are not supported
--> $DIR/issue-33418.rs:5:10
|
LL | trait Tr3: !SuperA + SuperB {} //~ ERROR negative trait bounds are not supported
| ^^^^^^^^^---------
| |
| help: remove the trait bound

error: negative trait bounds are not supported
--> $DIR/issue-33418.rs:6:10
|
LL | trait Tr4: !SuperA + SuperB //~ ERROR negative trait bounds are not supported
| __________-^^^^^^^^
LL | | + !SuperC + SuperD {}
| |_____^^^^^^^^^________- help: remove the trait bounds

error: negative trait bounds are not supported
--> $DIR/issue-33418.rs:8:10
|
LL | trait Tr5: !SuperA //~ ERROR negative trait bounds are not supported
| __________-^^^^^^^^
LL | | + !SuperB {}
| | ^^^^^^^^-
| |_____________|
| help: remove the trait bounds

error: aborting due to 5 previous errors