Make lifetime errors more precise in the presence of Fresh lifetimes.

Author: cjgillot

compiler/rustc_hir/src/hir.rs

@@ -131,6 +131,17 @@ impl LifetimeName {
         }
     }
 
+    pub fn is_anonymous(&self) -> bool {
+        match *self {
+            LifetimeName::ImplicitObjectLifetimeDefault
+            | LifetimeName::Implicit
+            | LifetimeName::Underscore
+            | LifetimeName::Param(ParamName::Fresh(_))
+            | LifetimeName::Error => true,
+            LifetimeName::Static | LifetimeName::Param(_) => false,
+        }
+    }
+
     pub fn is_elided(&self) -> bool {
         match self {
             LifetimeName::ImplicitObjectLifetimeDefault

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -72,7 +72,7 @@ use rustc_middle::ty::{
     subst::{GenericArgKind, Subst, SubstsRef},
     Binder, EarlyBinder, List, Region, Ty, TyCtxt, TypeFoldable,
 };
-use rustc_span::{sym, BytePos, DesugaringKind, Pos, Span};
+use rustc_span::{sym, symbol::kw, BytePos, DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;
 use std::ops::ControlFlow;
 use std::{cmp, fmt, iter};
@@ -161,7 +161,12 @@ fn msg_span_from_early_bound_and_free_regions<'tcx>(
             {
                 sp = param.span;
             }
-            (format!("the lifetime `{}` as defined here", br.name), sp)
+            let text = if br.name == kw::UnderscoreLifetime {
+                format!("the anonymous lifetime as defined here")
+            } else {
+                format!("the lifetime `{}` as defined here", br.name)
+            };
+            (text, sp)
         }
         ty::ReFree(ty::FreeRegion {
             bound_region: ty::BoundRegionKind::BrNamed(_, name), ..
@@ -172,7 +177,12 @@ fn msg_span_from_early_bound_and_free_regions<'tcx>(
             {
                 sp = param.span;
             }
-            (format!("the lifetime `{}` as defined here", name), sp)
+            let text = if name == kw::UnderscoreLifetime {
+                format!("the anonymous lifetime as defined here")
+            } else {
+                format!("the lifetime `{}` as defined here", name)
+            };
+            (text, sp)
         }
         ty::ReFree(ref fr) => match fr.bound_region {
             ty::BrAnon(idx) => {

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs

@@ -12,6 +12,7 @@ use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::{GenericParamKind, Ty};
 use rustc_middle::ty::Region;
+use rustc_span::symbol::kw;
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     /// Print the error message for lifetime errors when both the concerned regions are anonymous.
@@ -169,7 +170,7 @@ pub fn suggest_adding_lifetime_params<'tcx>(
         return false;
     };
 
-    if !lifetime_sub.name.is_elided() || !lifetime_sup.name.is_elided() {
+    if !lifetime_sub.name.is_anonymous() || !lifetime_sup.name.is_anonymous() {
         return false;
     };
 
@@ -188,32 +189,37 @@ pub fn suggest_adding_lifetime_params<'tcx>(
         _ => return false,
     };
 
-    let (suggestion_param_name, introduce_new) = generics
+    let suggestion_param_name = generics
         .params
         .iter()
-        .find(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
-        .and_then(|p| tcx.sess.source_map().span_to_snippet(p.span).ok())
-        .map(|name| (name, false))
-        .unwrap_or_else(|| ("'a".to_string(), true));
-
-    let mut suggestions = vec![
-        if let hir::LifetimeName::Underscore = lifetime_sub.name {
-            (lifetime_sub.span, suggestion_param_name.clone())
+        .filter(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
+        .map(|p| p.name.ident().name)
+        .find(|i| *i != kw::UnderscoreLifetime);
+    let introduce_new = suggestion_param_name.is_none();
+    let suggestion_param_name =
+        suggestion_param_name.map(|n| n.to_string()).unwrap_or_else(|| "'a".to_owned());
+
+    debug!(?lifetime_sup.span);
+    debug!(?lifetime_sub.span);
+    let make_suggestion = |span: rustc_span::Span| {
+        if span.is_empty() {
+            (span, format!("{}, ", suggestion_param_name))
+        } else if let Ok("&") = tcx.sess.source_map().span_to_snippet(span).as_deref() {
+            (span.shrink_to_hi(), format!("{} ", suggestion_param_name))
         } else {
-            (lifetime_sub.span.shrink_to_hi(), suggestion_param_name.clone() + " ")
-        },
-        if let hir::LifetimeName::Underscore = lifetime_sup.name {
-            (lifetime_sup.span, suggestion_param_name.clone())
-        } else {
-            (lifetime_sup.span.shrink_to_hi(), suggestion_param_name.clone() + " ")
-        },
-    ];
+            (span, suggestion_param_name.clone())
+        }
+    };
+    let mut suggestions =
+        vec![make_suggestion(lifetime_sub.span), make_suggestion(lifetime_sup.span)];
 
     if introduce_new {
-        let new_param_suggestion = match &generics.params {
-            [] => (generics.span, format!("<{}>", suggestion_param_name)),
-            [first, ..] => (first.span.shrink_to_lo(), format!("{}, ", suggestion_param_name)),
-        };
+        let new_param_suggestion =
+            if let Some(first) = generics.params.iter().find(|p| !p.name.ident().span.is_empty()) {
+                (first.span.shrink_to_lo(), format!("{}, ", suggestion_param_name))
+            } else {
+                (generics.span, format!("<{}>", suggestion_param_name))
+            };
 
         suggestions.push(new_param_suggestion);
     }

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs

@@ -4,6 +4,7 @@ use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_middle::ty;
+use rustc_span::symbol::kw;
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     /// When given a `ConcreteFailure` for a function with parameters containing a named region and
@@ -67,7 +68,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let is_impl_item = region_info.is_impl_item;
 
         match br {
-            ty::BrAnon(_) => {}
+            ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) => {}
             _ => {
                 /* not an anonymous region */
                 debug!("try_report_named_anon_conflict: not an anonymous region");

src/test/ui/async-await/issue-76547.base.stderr

@@ -5,6 +5,12 @@ LL | async fn fut(bufs: &mut [&mut [u8]]) {
    |                    ---------------- these two types are declared with different lifetimes...
 LL |     ListFut(bufs).await
    |             ^^^^ ...but data from `bufs` flows into `bufs` here
+   |
+   = note: each elided lifetime in input position becomes a distinct lifetime
+help: consider introducing a named lifetime parameter
+   |
+LL | async fn fut<'a>(bufs: &'a mut [&'a mut [u8]]) {
+   |             ++++        ++       ++
 
 error[E0623]: lifetime mismatch
   --> $DIR/issue-76547.rs:39:14
@@ -13,6 +19,12 @@ LL | async fn fut2(bufs: &mut [&mut [u8]]) -> i32 {
    |                     ---------------- these two types are declared with different lifetimes...
 LL |     ListFut2(bufs).await
    |              ^^^^ ...but data from `bufs` flows into `bufs` here
+   |
+   = note: each elided lifetime in input position becomes a distinct lifetime
+help: consider introducing a named lifetime parameter
+   |
+LL | async fn fut2<'a>(bufs: &'a mut [&'a mut [u8]]) -> i32 {
+   |              ++++        ++       ++
 
 error: aborting due to 2 previous errors
 

src/test/ui/async-await/issue-76547.nll.stderr

@@ -7,6 +7,11 @@ LL | async fn fut(bufs: &mut [&mut [u8]]) {
    |                    let's call the lifetime of this reference `'1`
 LL |     ListFut(bufs).await
    |             ^^^^ this usage requires that `'1` must outlive `'2`
+   |
+help: consider introducing a named lifetime parameter
+   |
+LL | async fn fut<'a>(bufs: &'a mut [&'a mut [u8]]) {
+   |             ++++        ++       ++
 
 error: lifetime may not live long enough
   --> $DIR/issue-76547.rs:39:14
@@ -17,6 +22,11 @@ LL | async fn fut2(bufs: &mut [&mut [u8]]) -> i32 {
    |                     let's call the lifetime of this reference `'1`
 LL |     ListFut2(bufs).await
    |              ^^^^ this usage requires that `'1` must outlive `'2`
+   |
+help: consider introducing a named lifetime parameter
+   |
+LL | async fn fut2<'a>(bufs: &'a mut [&'a mut [u8]]) -> i32 {
+   |              ++++        ++       ++
 
 error: aborting due to 2 previous errors
 

src/test/ui/async-await/issues/issue-63388-1.base.stderr

@@ -1,14 +1,12 @@
-error[E0623]: lifetime mismatch
+error[E0621]: explicit lifetime required in the type of `foo`
   --> $DIR/issue-63388-1.rs:19:9
    |
 LL |         &'a self, foo: &dyn Foo
-   |                        -------- this parameter and the return type are declared with different lifetimes...
-LL |     ) -> &dyn Foo
-   |          --------
+   |                        -------- help: add explicit lifetime `'a` to the type of `foo`: `&'a (dyn Foo + 'a)`
 ...
 LL |         foo
-   |         ^^^ ...but data from `foo` is returned here
+   |         ^^^ lifetime `'a` required
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0623`.
+For more information about this error, try `rustc --explain E0621`.

src/test/ui/async-await/issues/issue-63388-1.nll.stderr

@@ -1,17 +1,16 @@
-error: lifetime may not live long enough
+error[E0621]: explicit lifetime required in the type of `foo`
   --> $DIR/issue-63388-1.rs:17:5
    |
-LL |       async fn do_sth<'a>(
-   |                       -- lifetime `'a` defined here
 LL |           &'a self, foo: &dyn Foo
-   |                          - let's call the lifetime of this reference `'1`
+   |                          -------- help: add explicit lifetime `'a` to the type of `foo`: `&'a (dyn Foo + 'a)`
 LL |       ) -> &dyn Foo
 LL | /     {
 LL | |
 LL | |         foo
 LL | |
 LL | |     }
-   | |_____^ associated function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
+   | |_____^ lifetime `'a` required
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0621`.

src/test/ui/async-await/issues/issue-63388-1.rs

@@ -15,9 +15,9 @@ impl Xyz {
         &'a self, foo: &dyn Foo
     ) -> &dyn Foo
     {
-        //[nll]~^ ERROR lifetime may not live long enough
+        //[nll]~^ ERROR explicit lifetime required in the type of `foo` [E0621]
         foo
-        //[base]~^ ERROR lifetime mismatch
+        //[base]~^ ERROR explicit lifetime required in the type of `foo` [E0621]
     }
 }
 

src/test/ui/error-codes/E0308-2.stderr

@@ -6,7 +6,7 @@ LL | impl Eq for &dyn DynEq {}
    |
    = note: expected trait `<&dyn DynEq as PartialEq>`
               found trait `<&(dyn DynEq + 'static) as PartialEq>`
-note: the lifetime `'_` as defined here...
+note: the anonymous lifetime as defined here...
   --> $DIR/E0308-2.rs:9:13
    |
 LL | impl Eq for &dyn DynEq {}