Only make suggestion when type is Copy.
This commit makes the suggestion to dereference when a type implements `Deref` only apply if the dereference would succeed (ie. the type is `Copy`, otherwise a borrow check error would occur).
This commit is contained in:
David Wood
parent
fd95ba3574
commit
7ab1bfd692
9 changed files with 91 additions and 75 deletions
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@ -324,8 +324,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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sp,
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);
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match (&expected.sty, &checked_ty.sty) {
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(&ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.sty, &check.sty) {
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// Check the `expn_info()` to see if this is a macro; if so, it's hard to
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// extract the text and make a good suggestion, so don't bother.
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let is_macro = sp.ctxt().outer().expn_info().is_some();
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match (&expr.node, &expected.sty, &checked_ty.sty) {
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(_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.sty, &check.sty) {
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(&ty::Str, &ty::Array(arr, _)) |
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(&ty::Str, &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
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if let hir::ExprKind::Lit(_) = expr.node {
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@ -352,7 +356,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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}
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_ => {}
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},
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(&ty::Ref(_, _, mutability), _) => {
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(_, &ty::Ref(_, _, mutability), _) => {
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// Check if it can work when put into a ref. For example:
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//
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// ```
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@ -407,28 +411,20 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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});
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}
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}
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}
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(_, &ty::Ref(_, checked, _)) => {
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},
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(hir::ExprKind::AddrOf(_, ref expr), _, &ty::Ref(_, checked, _)) if {
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self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
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} => {
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// We have `&T`, check if what was expected was `T`. If so,
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// we may want to suggest adding a `*`, or removing
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// a `&`.
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//
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// (But, also check the `expn_info()` to see if this is
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// a macro; if so, it's hard to extract the text and make a good
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// suggestion, so don't bother.)
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if self.infcx.can_sub(self.param_env, checked, &expected).is_ok() &&
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sp.ctxt().outer().expn_info().is_none() {
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match expr.node {
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// Maybe remove `&`?
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hir::ExprKind::AddrOf(_, ref expr) => {
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// we may want to suggest removing a `&`.
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if !cm.span_to_filename(expr.span).is_real() {
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if let Ok(code) = cm.span_to_snippet(sp) {
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if code.chars().next() == Some('&') {
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return Some((
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sp,
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"consider removing the borrow",
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code[1..].to_string()),
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);
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code[1..].to_string(),
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));
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}
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}
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return None;
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@ -436,36 +432,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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if let Ok(code) = cm.span_to_snippet(expr.span) {
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return Some((sp, "consider removing the borrow", code));
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}
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}
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// Maybe add `*`? Only if `T: Copy`.
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_ => {
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if self.infcx.type_is_copy_modulo_regions(self.param_env,
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checked,
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sp) {
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// do not suggest if the span comes from a macro (#52783)
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if let (Ok(code), true) = (
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cm.span_to_snippet(sp),
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sp == expr.span,
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) {
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return Some((
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sp,
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"consider dereferencing the borrow",
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if is_struct_pat_shorthand_field {
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format!("{}: *{}", code, code)
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} else {
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format!("*{}", code)
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},
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));
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}
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}
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}
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}
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}
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}
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_ => {
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// If neither type is a reference, then check for `Deref` implementations by
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// constructing a predicate to prove: `<T as Deref>::Output == U`
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_ if sp == expr.span && !is_macro => {
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// Check for `Deref` implementations by constructing a predicate to
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// prove: `<T as Deref>::Output == U`
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let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
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let item_def_id = self.tcx.associated_items(deref_trait).next().unwrap().def_id;
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let predicate = ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
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@ -483,17 +453,28 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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ty: expected,
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}));
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let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
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if self.infcx.predicate_may_hold(&obligation) {
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if let (Ok(code), true) = (cm.span_to_snippet(sp), sp == expr.span) {
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let msg = if is_struct_pat_shorthand_field {
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let impls_deref = self.infcx.predicate_may_hold(&obligation);
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// For a suggestion to make sense, the type would need to be `Copy`.
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let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);
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if is_copy && impls_deref {
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if let Ok(code) = cm.span_to_snippet(sp) {
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let message = if checked_ty.is_region_ptr() {
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"consider dereferencing the borrow"
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} else {
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"consider dereferencing the type"
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};
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let suggestion = if is_struct_pat_shorthand_field {
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format!("{}: *{}", code, code)
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} else {
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format!("*{}", code)
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};
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return Some((sp, "consider dereferencing the type", msg));
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return Some((sp, message, suggestion));
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}
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}
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}
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_ => {}
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}
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None
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}
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@ -5,7 +5,7 @@ LL | x = box x;
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| ^^^^^
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| |
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| cyclic type of infinite size
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| help: consider dereferencing the type: `*box x`
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| help: try using a conversion method: `box x.to_string()`
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error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
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--> $DIR/infinite-autoderef.rs:25:5
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@ -5,7 +5,7 @@ LL | f = box g;
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| ^^^^^
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| |
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| cyclic type of infinite size
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| help: consider dereferencing the type: `*box g`
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| help: try using a conversion method: `box g.to_string()`
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error: aborting due to previous error
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@ -5,7 +5,7 @@ LL | f = box f;
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| ^^^^^
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| |
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| cyclic type of infinite size
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| help: consider dereferencing the type: `*box f`
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| help: try using a conversion method: `box f.to_string()`
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error: aborting due to previous error
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@ -44,7 +44,7 @@ LL | f = box f;
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| ^^^^^
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| |
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| cyclic type of infinite size
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| help: consider dereferencing the type: `*box f`
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| help: try using a conversion method: `box f.to_string()`
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error[E0308]: mismatched types
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--> $DIR/coerce-suggestions.rs:21:9
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@ -7,9 +7,18 @@
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struct Foo(i32);
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struct Bar(String);
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impl std::ops::Deref for Foo {
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type Target = i32;
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fn deref(&self) -> &i32 {
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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impl std::ops::Deref for Bar {
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type Target = String;
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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@ -19,4 +28,8 @@ fn main() {
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let y: i32 = *x; //~ ERROR mismatched types
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let a = &42;
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let b: i32 = *a; //~ ERROR mismatched types
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// Do not make a suggestion when adding a `*` wouldn't actually fix the issue:
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let f = Bar("bar".to_string());
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let g: String = f.to_string(); //~ ERROR mismatched types
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}
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@ -7,9 +7,18 @@
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struct Foo(i32);
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struct Bar(String);
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impl std::ops::Deref for Foo {
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type Target = i32;
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fn deref(&self) -> &i32 {
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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impl std::ops::Deref for Bar {
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type Target = String;
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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@ -19,4 +28,8 @@ fn main() {
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let y: i32 = x; //~ ERROR mismatched types
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let a = &42;
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let b: i32 = a; //~ ERROR mismatched types
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// Do not make a suggestion when adding a `*` wouldn't actually fix the issue:
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let f = Bar("bar".to_string());
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let g: String = f; //~ ERROR mismatched types
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}
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@ -1,5 +1,5 @@
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error[E0308]: mismatched types
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--> $DIR/issue-59819.rs:19:18
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--> $DIR/issue-59819.rs:28:18
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LL | let y: i32 = x;
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| ^
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@ -11,7 +11,7 @@ LL | let y: i32 = x;
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found type `Foo`
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error[E0308]: mismatched types
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--> $DIR/issue-59819.rs:21:18
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--> $DIR/issue-59819.rs:30:18
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LL | let b: i32 = a;
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| ^
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@ -22,6 +22,18 @@ LL | let b: i32 = a;
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= note: expected type `i32`
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found type `&{integer}`
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error: aborting due to 2 previous errors
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error[E0308]: mismatched types
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--> $DIR/issue-59819.rs:34:21
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LL | let g: String = f;
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| ^
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| |
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| expected struct `std::string::String`, found struct `Bar`
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| help: try using a conversion method: `f.to_string()`
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= note: expected type `std::string::String`
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found type `Bar`
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error: aborting due to 3 previous errors
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For more information about this error, try `rustc --explain E0308`.
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@ -2,10 +2,7 @@ error[E0308]: mismatched types
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--> $DIR/terr-sorts.rs:10:14
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LL | want_foo(b);
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| ^
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| |
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| expected struct `Foo`, found struct `std::boxed::Box`
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| help: consider dereferencing the type: `*b`
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| ^ expected struct `Foo`, found struct `std::boxed::Box`
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= note: expected type `Foo`
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found type `std::boxed::Box<Foo>`
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