Improve help for recursion limit errors

compiler/rustc_expand/src/expand.rs

@@ -633,14 +633,18 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
     fn error_recursion_limit_reached(&mut self) {
         let expn_data = self.cx.current_expansion.id.expn_data();
-        let suggested_limit = self.cx.ecfg.recursion_limit * 2;
+        let suggested_limit = match self.cx.ecfg.recursion_limit {
+            Limit(0) => Limit(2),
+            limit => limit * 2,
+        };
         self.cx
             .struct_span_err(
                 expn_data.call_site,
                 &format!("recursion limit reached while expanding `{}`", expn_data.kind.descr()),
             )
             .help(&format!(
-                "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
+                "consider increasing the recursion limit by adding a \
+                 `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
                 suggested_limit, self.cx.ecfg.crate_name,
             ))
             .emit();

compiler/rustc_trait_selection/src/autoderef.rs

@@ -5,7 +5,7 @@ use rustc_hir as hir;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt, WithConstness};
 use rustc_middle::ty::{ToPredicate, TypeFoldable};
-use rustc_session::DiagnosticMessageId;
+use rustc_session::{DiagnosticMessageId, Limit};
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::Span;
 
@@ -217,7 +217,10 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
 
 pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
     // We've reached the recursion limit, error gracefully.
-    let suggested_limit = tcx.recursion_limit() * 2;
+    let suggested_limit = match tcx.recursion_limit() {
+        Limit(0) => Limit(2),
+        limit => limit * 2,
+    };
     let msg = format!("reached the recursion limit while auto-dereferencing `{:?}`", ty);
     let error_id = (DiagnosticMessageId::ErrorId(55), Some(span), msg);
     let fresh = tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
@@ -231,7 +234,8 @@ pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Spa
         )
         .span_label(span, "deref recursion limit reached")
         .help(&format!(
-            "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
+            "consider increasing the recursion limit by adding a \
+             `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
             suggested_limit,
             tcx.crate_name(LOCAL_CRATE),
         ))

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -22,6 +22,7 @@ use rustc_middle::ty::{
     Infer, InferTy, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
 };
 use rustc_middle::ty::{TypeAndMut, TypeckResults};
+use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, DesugaringKind, ExpnKind, ForLoopLoc, MultiSpan, Span, DUMMY_SP};
@@ -2426,10 +2427,13 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
     }
 
     fn suggest_new_overflow_limit(&self, err: &mut DiagnosticBuilder<'_>) {
-        let current_limit = self.tcx.recursion_limit();
-        let suggested_limit = current_limit * 2;
+        let suggested_limit = match self.tcx.recursion_limit() {
+            Limit(0) => Limit(2),
+            limit => limit * 2,
+        };
         err.help(&format!(
-            "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
+            "consider increasing the recursion limit by adding a \
+             `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
             suggested_limit,
             self.tcx.crate_name(LOCAL_CRATE),
         ));

src/test/ui/associated-types/hr-associated-type-bound-2.stderr

@@ -9,7 +9,7 @@ LL | |     type U = str;
 LL | | }
    | |_^
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`hr_associated_type_bound_2`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`hr_associated_type_bound_2`)
 note: required because of the requirements on the impl of `for<'b> X<'b>` for `u32`
   --> $DIR/hr-associated-type-bound-2.rs:11:6
    |
@@ -24,7 +24,7 @@ error[E0275]: overflow evaluating the requirement `for<'b> u32: X<'b>`
 LL |     type U = str;
    |     ^^^^^^^^^^^^^
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`hr_associated_type_bound_2`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`hr_associated_type_bound_2`)
 note: required because of the requirements on the impl of `for<'b> X<'b>` for `u32`
   --> $DIR/hr-associated-type-bound-2.rs:11:6
    |

src/test/ui/autoref-autoderef/issue-38940.stderr

@@ -4,7 +4,7 @@ error[E0055]: reached the recursion limit while auto-dereferencing `J`
 LL |     let x: &Bottom = &t;
    |                      ^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="20"]` attribute to your crate (`issue_38940`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`issue_38940`)
 
 error[E0308]: mismatched types
   --> $DIR/issue-38940.rs:43:22

src/test/ui/did_you_mean/recursion_limit.stderr

@@ -4,7 +4,7 @@ error[E0275]: overflow evaluating the requirement `K: Send`
 LL |     is_send::<A>();
    |     ^^^^^^^^^^^^
    |
-   = help: consider adding a `#![recursion_limit="20"]` attribute to your crate (`recursion_limit`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`recursion_limit`)
 note: required because it appears within the type `J`
   --> $DIR/recursion_limit.rs:24:9
    |

src/test/ui/did_you_mean/recursion_limit_deref.stderr

@@ -4,7 +4,7 @@ error[E0055]: reached the recursion limit while auto-dereferencing `J`
 LL |     let x: &Bottom = &t;
    |                      ^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="20"]` attribute to your crate (`recursion_limit_deref`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`recursion_limit_deref`)
 
 error[E0308]: mismatched types
   --> $DIR/recursion_limit_deref.rs:50:22

src/test/ui/did_you_mean/recursion_limit_macro.stderr

@@ -7,7 +7,7 @@ LL |     ($t:tt $($tail:tt)*) => { recurse!($($tail)*) };
 LL |     recurse!(0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9);
    |     -------------------------------------------------- in this macro invocation
    |
-   = help: consider adding a `#![recursion_limit="20"]` attribute to your crate (`recursion_limit_macro`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`recursion_limit_macro`)
    = note: this error originates in the macro `recurse` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/error-codes/E0055.stderr

@@ -4,7 +4,7 @@ error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
 LL |     ref_foo.foo();
    |             ^^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="8"]` attribute to your crate (`E0055`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "8"]` attribute to your crate (`E0055`)
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0275.stderr

@@ -4,7 +4,7 @@ error[E0275]: overflow evaluating the requirement `Bar<Bar<Bar<Bar<Bar<Bar<Bar<B
 LL | impl<T> Foo for T where Bar<T>: Foo {}
    |                                 ^^^
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`E0275`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`E0275`)
 note: required because of the requirements on the impl of `Foo` for `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
   --> $DIR/E0275.rs:5:9
    |

src/test/ui/infinite/infinite-autoderef.stderr

@@ -12,15 +12,15 @@ error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
 LL |     Foo.foo;
    |     ^^^^^^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`infinite_autoderef`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)
 
 error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
   --> $DIR/infinite-autoderef.rs:25:9
    |
 LL |     Foo.foo;
    |         ^^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`infinite_autoderef`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)
 
 error[E0609]: no field `foo` on type `Foo`
   --> $DIR/infinite-autoderef.rs:25:9
@@ -34,7 +34,7 @@ error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
 LL |     Foo.bar();
    |         ^^^ deref recursion limit reached
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`infinite_autoderef`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)
 
 error[E0599]: no method named `bar` found for struct `Foo` in the current scope
   --> $DIR/infinite-autoderef.rs:26:9

src/test/ui/infinite/infinite-macro-expansion.stderr

@@ -7,7 +7,7 @@ LL |     () => (recursive!())
 LL |     recursive!()
    |     ------------ in this macro invocation
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`infinite_macro_expansion`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_macro_expansion`)
    = note: this error originates in the macro `recursive` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/issues/issue-16098.stderr

@@ -7,7 +7,7 @@ LL |             $n + prob1!($n - 1);
 LL |     println!("Problem 1: {}", prob1!(1000));
    |                               ------------ in this macro invocation
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`issue_16098`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_16098`)
    = note: this error originates in the macro `prob1` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/issues/issue-18400.stderr

@@ -4,7 +4,7 @@ error[E0275]: overflow evaluating the requirement `_: Sized`
 LL |     0.contains(bits);
    |       ^^^^^^^^
    |
-   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate (`issue_18400`)
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_18400`)
 note: required because of the requirements on the impl of `Set<&[_]>` for `{integer}`
   --> $DIR/issue-18400.rs:6:16
    |