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Rollup merge of #98183 - dtolnay:emptybound, r=lcnr
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Fix pretty printing of empty bound lists in where-clause

Repro:

```rust
macro_rules! assert_item_stringify {
    ($item:item $expected:literal) => {
        assert_eq!(stringify!($item), $expected);
    };
}

fn main() {
    assert_item_stringify! {
        fn f<'a, T>() where 'a:, T: {}
        "fn f<'a, T>() where 'a:, T: {}"
    }
}
```

Previously this assertion would fail because rustc renders the where-clause as `where 'a, T` which is invalid syntax.

This PR makes the above assertion pass.

This bug also affects `-Zunpretty=expanded`. The intention is for that to emit syntactically valid code, but the buggy output is not valid Rust syntax.

```console
$ rustc <(echo "fn f<'a, T>() where 'a:, T: {}") -Zunpretty=expanded
#![feature(prelude_import)]
#![no_std]
#[prelude_import]
use ::std::prelude::rust_2015::*;
#[macro_use]
extern crate std;
fn f<'a, T>() where 'a, T {}
```

```console
$ rustc <(echo "fn f<'a, T>() where 'a:, T: {}") -Zunpretty=expanded | rustc -
error: expected `:`, found `,`
 --> <anon>:7:23
  |
7 | fn f<'a, T>() where 'a, T {}
  |                       ^ expected `:`
```
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@JohnTitor
JohnTitor authored Jun 20, 2022
2 parents 9a0b774 + fe9635f commit b6fb582
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Showing 4 changed files with 79 additions and 50 deletions.
93 changes: 49 additions & 44 deletions compiler/rustc_ast_pretty/src/pprust/state.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -814,7 +814,7 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
}

fn bounds_to_string(&self, bounds: &[ast::GenericBound]) -> String {
Self::to_string(|s| s.print_type_bounds("", bounds))
Self::to_string(|s| s.print_type_bounds(bounds))
}

fn pat_to_string(&self, pat: &ast::Pat) -> String {
Expand Down Expand Up @@ -991,7 +991,12 @@ impl<'a> State<'a> {
Term::Const(c) => self.print_expr_anon_const(c, &[]),
}
}
ast::AssocConstraintKind::Bound { bounds } => self.print_type_bounds(":", &*bounds),
ast::AssocConstraintKind::Bound { bounds } => {
if !bounds.is_empty() {
self.word_nbsp(":");
self.print_type_bounds(&bounds);
}
}
}
}

Expand Down Expand Up @@ -1045,11 +1050,14 @@ impl<'a> State<'a> {
}
ast::TyKind::Path(Some(ref qself), ref path) => self.print_qpath(path, qself, false),
ast::TyKind::TraitObject(ref bounds, syntax) => {
let prefix = if syntax == ast::TraitObjectSyntax::Dyn { "dyn" } else { "" };
self.print_type_bounds(prefix, &bounds);
if syntax == ast::TraitObjectSyntax::Dyn {
self.word_nbsp("dyn");
}
self.print_type_bounds(bounds);
}
ast::TyKind::ImplTrait(_, ref bounds) => {
self.print_type_bounds("impl", &bounds);
self.word_nbsp("impl");
self.print_type_bounds(bounds);
}
ast::TyKind::Array(ref ty, ref length) => {
self.word("[");
Expand Down Expand Up @@ -1549,29 +1557,24 @@ impl<'a> State<'a> {
}
}

pub fn print_type_bounds(&mut self, prefix: &'static str, bounds: &[ast::GenericBound]) {
if !bounds.is_empty() {
self.word(prefix);
let mut first = true;
for bound in bounds {
if !(first && prefix.is_empty()) {
self.nbsp();
}
if first {
first = false;
} else {
self.word_space("+");
}
pub fn print_type_bounds(&mut self, bounds: &[ast::GenericBound]) {
let mut first = true;
for bound in bounds {
if first {
first = false;
} else {
self.nbsp();
self.word_space("+");
}

match bound {
GenericBound::Trait(tref, modifier) => {
if modifier == &TraitBoundModifier::Maybe {
self.word("?");
}
self.print_poly_trait_ref(tref);
match bound {
GenericBound::Trait(tref, modifier) => {
if modifier == &TraitBoundModifier::Maybe {
self.word("?");
}
GenericBound::Outlives(lt) => self.print_lifetime(*lt),
self.print_poly_trait_ref(tref);
}
GenericBound::Outlives(lt) => self.print_lifetime(*lt),
}
}
}
Expand All @@ -1580,22 +1583,14 @@ impl<'a> State<'a> {
self.print_name(lifetime.ident.name)
}

pub(crate) fn print_lifetime_bounds(
&mut self,
lifetime: ast::Lifetime,
bounds: &ast::GenericBounds,
) {
self.print_lifetime(lifetime);
if !bounds.is_empty() {
self.word(": ");
for (i, bound) in bounds.iter().enumerate() {
if i != 0 {
self.word(" + ");
}
match bound {
ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt),
_ => panic!(),
}
pub(crate) fn print_lifetime_bounds(&mut self, bounds: &ast::GenericBounds) {
for (i, bound) in bounds.iter().enumerate() {
if i != 0 {
self.word(" + ");
}
match bound {
ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt),
_ => panic!(),
}
}
}
Expand All @@ -1613,11 +1608,18 @@ impl<'a> State<'a> {
match param.kind {
ast::GenericParamKind::Lifetime => {
let lt = ast::Lifetime { id: param.id, ident: param.ident };
s.print_lifetime_bounds(lt, &param.bounds)
s.print_lifetime(lt);
if !param.bounds.is_empty() {
s.word_nbsp(":");
s.print_lifetime_bounds(&param.bounds)
}
}
ast::GenericParamKind::Type { ref default } => {
s.print_ident(param.ident);
s.print_type_bounds(":", &param.bounds);
if !param.bounds.is_empty() {
s.word_nbsp(":");
s.print_type_bounds(&param.bounds);
}
if let Some(ref default) = default {
s.space();
s.word_space("=");
Expand All @@ -1630,7 +1632,10 @@ impl<'a> State<'a> {
s.space();
s.word_space(":");
s.print_type(ty);
s.print_type_bounds(":", &param.bounds);
if !param.bounds.is_empty() {
s.word_nbsp(":");
s.print_type_bounds(&param.bounds);
}
if let Some(ref default) = default {
s.space();
s.word_space("=");
Expand Down
28 changes: 23 additions & 5 deletions compiler/rustc_ast_pretty/src/pprust/state/item.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,10 @@ impl<'a> State<'a> {
self.word_space("type");
self.print_ident(ident);
self.print_generic_params(&generics.params);
self.print_type_bounds(":", bounds);
if !bounds.is_empty() {
self.word_nbsp(":");
self.print_type_bounds(bounds);
}
self.print_where_clause_parts(where_clauses.0.0, before_predicates);
if let Some(ty) = ty {
self.space();
Expand Down Expand Up @@ -320,7 +323,10 @@ impl<'a> State<'a> {
real_bounds.push(b.clone());
}
}
self.print_type_bounds(":", &real_bounds);
if !real_bounds.is_empty() {
self.word_nbsp(":");
self.print_type_bounds(&real_bounds);
}
self.print_where_clause(&generics.where_clause);
self.word(" ");
self.bopen();
Expand All @@ -347,7 +353,10 @@ impl<'a> State<'a> {
}
}
self.nbsp();
self.print_type_bounds("=", &real_bounds);
if !real_bounds.is_empty() {
self.word_nbsp("=");
self.print_type_bounds(&real_bounds);
}
self.print_where_clause(&generics.where_clause);
self.word(";");
self.end(); // end inner head-block
Expand Down Expand Up @@ -618,14 +627,23 @@ impl<'a> State<'a> {
}) => {
self.print_formal_generic_params(bound_generic_params);
self.print_type(bounded_ty);
self.print_type_bounds(":", bounds);
self.word(":");
if !bounds.is_empty() {
self.nbsp();
self.print_type_bounds(bounds);
}
}
ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate {
lifetime,
bounds,
..
}) => {
self.print_lifetime_bounds(*lifetime, bounds);
self.print_lifetime(*lifetime);
self.word(":");
if !bounds.is_empty() {
self.nbsp();
self.print_lifetime_bounds(bounds);
}
}
ast::WherePredicate::EqPredicate(ast::WhereEqPredicate { lhs_ty, rhs_ty, .. }) => {
self.print_type(lhs_ty);
Expand Down
5 changes: 4 additions & 1 deletion compiler/rustc_parse/src/parser/diagnostics.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1355,7 +1355,10 @@ impl<'a> Parser<'a> {
s.print_mutability(mut_ty.mutbl, false);
s.popen();
s.print_type(&mut_ty.ty);
s.print_type_bounds(" +", &bounds);
if !bounds.is_empty() {
s.word(" + ");
s.print_type_bounds(&bounds);
}
s.pclose()
});

Expand Down
3 changes: 3 additions & 0 deletions src/test/pretty/where-clauses.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,4 +2,7 @@

fn f<'a, 'b, T>(t: T) -> isize where T: 'a, 'a: 'b, T: Eq { 0 }

// This is legal syntax, sometimes generated by macros. `where T: $($bound+)*`
fn zero_bounds<'a, T>() where 'a:, T: {}

fn main() {}

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