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Use structured suggestion when requiring Copy constraint in type param #66567

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merged 3 commits into from
Nov 29, 2019
Merged

Use structured suggestion when requiring Copy constraint in type param #66567

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02bc412
Use structured suggestion when requiring `Copy` constraint in type param
estebank Nov 20, 2019
9fb446d
Deduplicate type param constraint suggestion code
estebank Nov 20, 2019
0f530ec
review comments
estebank Nov 24, 2019
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156 changes: 91 additions & 65 deletions src/librustc/traits/error_reporting.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@ use syntax::ast;
use syntax::symbol::{sym, kw};
use syntax_pos::{DUMMY_SP, Span, ExpnKind, MultiSpan};
use rustc::hir::def_id::LOCAL_CRATE;
use syntax_pos::source_map::SourceMap;

use rustc_error_codes::*;

Expand Down Expand Up @@ -1091,7 +1092,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
}
fn suggest_restricting_param_bound(
&self,
err: &mut DiagnosticBuilder<'_>,
mut err: &mut DiagnosticBuilder<'_>,
trait_ref: &ty::PolyTraitRef<'_>,
body_id: hir::HirId,
) {
Expand All @@ -1102,7 +1103,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
_ => return,
};

let mut suggest_restriction = |generics: &hir::Generics, msg| {
let suggest_restriction = |
generics: &hir::Generics,
msg,
err: &mut DiagnosticBuilder<'_>,
| {
let span = generics.where_clause.span_for_predicates_or_empty_place();
if !span.from_expansion() && span.desugaring_kind().is_none() {
err.span_suggestion(
Expand Down Expand Up @@ -1132,7 +1137,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
kind: hir::TraitItemKind::Method(..), ..
}) if param_ty && self_ty == self.tcx.types.self_param => {
// Restricting `Self` for a single method.
suggest_restriction(&generics, "`Self`");
suggest_restriction(&generics, "`Self`", err);
return;
}

Expand All @@ -1154,7 +1159,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
kind: hir::ItemKind::Impl(_, _, _, generics, ..), ..
}) if projection.is_some() => {
// Missing associated type bound.
suggest_restriction(&generics, "the associated type");
suggest_restriction(&generics, "the associated type", err);
return;
}

Expand Down Expand Up @@ -1183,68 +1188,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
hir::Node::ImplItem(hir::ImplItem { generics, span, .. })
if param_ty => {
// Missing generic type parameter bound.
let restrict_msg = "consider further restricting this bound";
let param_name = self_ty.to_string();
for param in generics.params.iter().filter(|p| {
p.name.ident().as_str() == param_name
}) {
if param_name.starts_with("impl ") {
// `impl Trait` in argument:
// `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
err.span_suggestion(
param.span,
restrict_msg,
// `impl CurrentTrait + MissingTrait`
format!("{} + {}", param.name.ident(), trait_ref),
Applicability::MachineApplicable,
);
} else if generics.where_clause.predicates.is_empty() &&
param.bounds.is_empty()
{
// If there are no bounds whatsoever, suggest adding a constraint
// to the type parameter:
// `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
err.span_suggestion(
param.span,
"consider restricting this bound",
format!("{}", trait_ref.to_predicate()),
Applicability::MachineApplicable,
);
} else if !generics.where_clause.predicates.is_empty() {
// There is a `where` clause, so suggest expanding it:
// `fn foo<T>(t: T) where T: Debug {}` →
// `fn foo<T>(t: T) where T: Debug, T: Trait {}`
err.span_suggestion(
generics.where_clause.span().unwrap().shrink_to_hi(),
&format!(
"consider further restricting type parameter `{}`",
param_name,
),
format!(", {}", trait_ref.to_predicate()),
Applicability::MachineApplicable,
);
} else {
// If there is no `where` clause lean towards constraining to the
// type parameter:
// `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
// `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
let sp = param.span.with_hi(span.hi());
let span = self.tcx.sess.source_map()
.span_through_char(sp, ':');
if sp != param.span && sp != span {
// Only suggest if we have high certainty that the span
// covers the colon in `foo<T: Trait>`.
err.span_suggestion(span, restrict_msg, format!(
"{} + ",
trait_ref.to_predicate(),
), Applicability::MachineApplicable);
} else {
err.span_label(param.span, &format!(
"consider adding a `where {}` bound",
trait_ref.to_predicate(),
));
}
}
let constraint = trait_ref.to_string();
if suggest_constraining_type_param(
generics,
&mut err,
&param_name,
&constraint,
self.tcx.sess.source_map(),
*span,
) {
return;
}
}
Expand Down Expand Up @@ -2546,3 +2499,76 @@ impl ArgKind {
}
}
}

/// Suggest restricting a type param with a new bound.
pub fn suggest_constraining_type_param(
generics: &hir::Generics,
err: &mut DiagnosticBuilder<'_>,
param_name: &str,
constraint: &str,
source_map: &SourceMap,
span: Span,
) -> bool {
let restrict_msg = "consider further restricting this bound";
if let Some(param) = generics.params.iter().filter(|p| {
p.name.ident().as_str() == param_name
}).next() {
if param_name.starts_with("impl ") {
// `impl Trait` in argument:
// `fn foo(x: impl Trait) {}` → `fn foo(t: impl Trait + Trait2) {}`
err.span_suggestion(
param.span,
restrict_msg,
// `impl CurrentTrait + MissingTrait`
format!("{} + {}", param_name, constraint),
Applicability::MachineApplicable,
);
} else if generics.where_clause.predicates.is_empty() &&
param.bounds.is_empty()
{
// If there are no bounds whatsoever, suggest adding a constraint
// to the type parameter:
// `fn foo<T>(t: T) {}` → `fn foo<T: Trait>(t: T) {}`
err.span_suggestion(
param.span,
"consider restricting this bound",
format!("{}: {}", param_name, constraint),
Applicability::MachineApplicable,
);
} else if !generics.where_clause.predicates.is_empty() {
// There is a `where` clause, so suggest expanding it:
// `fn foo<T>(t: T) where T: Debug {}` →
// `fn foo<T>(t: T) where T: Debug, T: Trait {}`
err.span_suggestion(
generics.where_clause.span().unwrap().shrink_to_hi(),
&format!("consider further restricting type parameter `{}`", param_name),
format!(", {}: {}", param_name, constraint),
Applicability::MachineApplicable,
);
} else {
// If there is no `where` clause lean towards constraining to the
// type parameter:
// `fn foo<X: Bar, T>(t: T, x: X) {}` → `fn foo<T: Trait>(t: T) {}`
// `fn foo<T: Bar>(t: T) {}` → `fn foo<T: Bar + Trait>(t: T) {}`
let sp = param.span.with_hi(span.hi());
let span = source_map.span_through_char(sp, ':');
if sp != param.span && sp != span {
// Only suggest if we have high certainty that the span
// covers the colon in `foo<T: Trait>`.
err.span_suggestion(
span,
restrict_msg,
format!("{}: {} + ", param_name, constraint),
Applicability::MachineApplicable,
);
} else {
err.span_label(
param.span,
&format!("consider adding a `where {}: {}` bound", param_name, constraint),
);
}
}
return true;
}
false
}
18 changes: 11 additions & 7 deletions src/librustc_mir/borrow_check/conflict_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ use rustc::mir::{
PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, TerminatorKind, VarBindingForm,
};
use rustc::ty::{self, Ty};
use rustc::traits::error_reporting::suggest_constraining_type_param;
use rustc_data_structures::fx::FxHashSet;
use rustc_index::vec::Idx;
use rustc_errors::{Applicability, DiagnosticBuilder};
Expand Down Expand Up @@ -231,13 +232,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
if let ty::Param(param_ty) = ty.kind {
let tcx = self.infcx.tcx;
let generics = tcx.generics_of(self.mir_def_id);
let def_id = generics.type_param(&param_ty, tcx).def_id;
if let Some(sp) = tcx.hir().span_if_local(def_id) {
err.span_label(
sp,
"consider adding a `Copy` constraint to this type argument",
);
}
let param = generics.type_param(&param_ty, tcx);
let generics = tcx.hir().get_generics(self.mir_def_id).unwrap();
suggest_constraining_type_param(
generics,
&mut err,
&param.name.as_str(),
"Copy",
tcx.sess.source_map(),
span,
);
}
let span = if let Some(local) = place.as_local() {
let decl = &self.body.local_decls[local];
Expand Down
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