On recursive ADT, provide indirection structured suggestion

src/librustc_errors/diagnostic.rs

@@ -296,6 +296,29 @@ impl Diagnostic {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: suggestions
+                .into_iter()
+                .map(|suggestion| Substitution {
+                    parts: suggestion
+                        .into_iter()
+                        .map(|(span, snippet)| SubstitutionPart { snippet, span })
+                        .collect(),
+                })
+                .collect(),
+            msg: msg.to_owned(),
+            style: SuggestionStyle::ShowCode,
+            applicability,
+        });
+        self
+    }
+
     /// Prints out a message with for a multipart suggestion without showing the suggested code.
     ///
     /// This is intended to be used for suggestions that are obvious in what the changes need to

src/librustc_errors/diagnostic_builder.rs

@@ -260,6 +260,19 @@ impl<'a> DiagnosticBuilder<'a> {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        if !self.0.allow_suggestions {
+            return self;
+        }
+        self.0.diagnostic.multipart_suggestions(msg, suggestions, applicability);
+        self
+    }
+
     pub fn tool_only_multipart_suggestion(
         &mut self,
         msg: &str,

src/librustc_middle/ty/util.rs

@@ -827,7 +827,15 @@ impl<'tcx> ty::TyS<'tcx> {
                     // Find non representable fields with their spans
                     fold_repr(def.all_fields().map(|field| {
                         let ty = field.ty(tcx, substs);
-                        let span = tcx.hir().span_if_local(field.did).unwrap_or(sp);
+                        let span = match field
+                            .did
+                            .as_local()
+                            .map(|id| tcx.hir().as_local_hir_id(id))
+                            .and_then(|id| tcx.hir().find(id))
+                        {
+                            Some(hir::Node::Field(field)) => field.ty.span,
+                            _ => sp,
+                        };
                         match is_type_structurally_recursive(
                             tcx,
                             span,

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -1747,24 +1747,41 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
 pub fn recursive_type_with_infinite_size_error(
     tcx: TyCtxt<'tcx>,
     type_def_id: DefId,
-) -> DiagnosticBuilder<'tcx> {
+    spans: Vec<Span>,
+) {
     assert!(type_def_id.is_local());
     let span = tcx.hir().span_if_local(type_def_id).unwrap();
     let span = tcx.sess.source_map().guess_head_span(span);
-    let mut err = struct_span_err!(
-        tcx.sess,
-        span,
-        E0072,
-        "recursive type `{}` has infinite size",
-        tcx.def_path_str(type_def_id)
-    );
+    let path = tcx.def_path_str(type_def_id);
+    let mut err =
+        struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size", path);
     err.span_label(span, "recursive type has infinite size");
-    err.help(&format!(
-        "insert indirection (e.g., a `Box`, `Rc`, or `&`) \
-                           at some point to make `{}` representable",
-        tcx.def_path_str(type_def_id)
-    ));
-    err
+    for &span in &spans {
+        err.span_label(span, "recursive without indirection");
+    }
+    let msg = format!(
+        "insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `{}` representable",
+        path,
+    );
+    if spans.len() <= 4 {
+        err.multipart_suggestion(
+            &msg,
+            spans
+                .iter()
+                .flat_map(|&span| {
+                    vec![
+                        (span.shrink_to_lo(), "Box<".to_string()),
+                        (span.shrink_to_hi(), ">".to_string()),
+                    ]
+                    .into_iter()
+                })
+                .collect(),
+            Applicability::HasPlaceholders,
+        );
+    } else {
+        err.help(&msg);
+    }
+    err.emit();
 }
 
 /// Summarizes information

src/librustc_typeck/check/mod.rs

@@ -2390,11 +2390,7 @@ fn check_representable(tcx: TyCtxt<'_>, sp: Span, item_def_id: LocalDefId) -> bo
     // caught by case 1.
     match rty.is_representable(tcx, sp) {
         Representability::SelfRecursive(spans) => {
-            let mut err = recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id());
-            for span in spans {
-                err.span_label(span, "recursive without indirection");
-            }
-            err.emit();
+            recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id(), spans);
             return false;
         }
         Representability::Representable | Representability::ContainsRecursive => (),

src/test/ui/infinite/infinite-tag-type-recursion.stderr

@@ -6,7 +6,10 @@ LL | enum MList { Cons(isize, MList), Nil }
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `MList` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `MList` representable
+   |
+LL | enum MList { Cons(isize, Box<MList>), Nil }
+   |                          ^^^^     ^
 
 error[E0391]: cycle detected when computing drop-check constraints for `MList`
   --> $DIR/infinite-tag-type-recursion.rs:1:1

src/test/ui/issues/issue-17431-1.stderr

@@ -2,11 +2,14 @@ error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/issue-17431-1.rs:1:1
    |
 LL | struct Foo { foo: Option<Option<Foo>> }
-   | ^^^^^^^^^^   ------------------------ recursive without indirection
+   | ^^^^^^^^^^        ------------------- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | struct Foo { foo: Box<Option<Option<Foo>>> }
+   |                   ^^^^                   ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-17431-2.stderr

@@ -2,21 +2,27 @@ error[E0072]: recursive type `Baz` has infinite size
   --> $DIR/issue-17431-2.rs:1:1
    |
 LL | struct Baz { q: Option<Foo> }
-   | ^^^^^^^^^^   -------------- recursive without indirection
+   | ^^^^^^^^^^      ----------- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Baz` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Baz` representable
+   |
+LL | struct Baz { q: Box<Option<Foo>> }
+   |                 ^^^^           ^
 
 error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/issue-17431-2.rs:4:1
    |
 LL | struct Foo { q: Option<Baz> }
-   | ^^^^^^^^^^   -------------- recursive without indirection
+   | ^^^^^^^^^^      ----------- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | struct Foo { q: Box<Option<Baz>> }
+   |                 ^^^^           ^
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-17431-3.stderr

@@ -2,11 +2,14 @@ error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/issue-17431-3.rs:3:1
    |
 LL | struct Foo { foo: Mutex<Option<Foo>> }
-   | ^^^^^^^^^^   ----------------------- recursive without indirection
+   | ^^^^^^^^^^        ------------------ recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | struct Foo { foo: Box<Mutex<Option<Foo>>> }
+   |                   ^^^^                  ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-17431-4.stderr

@@ -2,11 +2,14 @@ error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/issue-17431-4.rs:3:1
    |
 LL | struct Foo<T> { foo: Option<Option<Foo<T>>>, marker: marker::PhantomData<T> }
-   | ^^^^^^^^^^^^^   --------------------------- recursive without indirection
+   | ^^^^^^^^^^^^^        ---------------------- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | struct Foo<T> { foo: Box<Option<Option<Foo<T>>>>, marker: marker::PhantomData<T> }
+   |                      ^^^^                      ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-17431-5.stderr

@@ -2,11 +2,14 @@ error[E0072]: recursive type `Bar` has infinite size
   --> $DIR/issue-17431-5.rs:5:1
    |
 LL | struct Bar<T> { x: Bar<Foo> , marker: marker::PhantomData<T> }
-   | ^^^^^^^^^^^^^   ----------- recursive without indirection
+   | ^^^^^^^^^^^^^      -------- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Bar` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Bar` representable
+   |
+LL | struct Bar<T> { x: Box<Bar<Foo>> , marker: marker::PhantomData<T> }
+   |                    ^^^^        ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-17431-6.stderr

@@ -6,7 +6,10 @@ LL | enum Foo { X(Mutex<Option<Foo>>) }
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | enum Foo { X(Box<Mutex<Option<Foo>>>) }
+   |              ^^^^                  ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-17431-7.stderr

@@ -6,7 +6,10 @@ LL | enum Foo { Voo(Option<Option<Foo>>) }
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL | enum Foo { Voo(Box<Option<Option<Foo>>>) }
+   |                ^^^^                   ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-2718-a.stderr

@@ -7,7 +7,10 @@ LL |     pub struct Pong(SendPacket<Ping>);
    |     |               recursive without indirection
    |     recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `pingpong::Pong` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `pingpong::Pong` representable
+   |
+LL |     pub struct Pong(Box<SendPacket<Ping>>);
+   |                     ^^^^                ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-3008-1.stderr

@@ -7,7 +7,10 @@ LL | enum Bar {
 LL |     BarSome(Bar)
    |             --- recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Bar` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Bar` representable
+   |
+LL |     BarSome(Box<Bar>)
+   |             ^^^^   ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-3008-2.stderr

@@ -2,11 +2,14 @@ error[E0072]: recursive type `Bar` has infinite size
   --> $DIR/issue-3008-2.rs:2:1
    |
 LL | struct Bar { x: Bar }
-   | ^^^^^^^^^^   ------ recursive without indirection
+   | ^^^^^^^^^^      --- recursive without indirection
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Bar` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Bar` representable
+   |
+LL | struct Bar { x: Box<Bar> }
+   |                 ^^^^   ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-3008-3.stderr

@@ -6,7 +6,10 @@ LL | enum E2<T> { V2(E2<E1>, marker::PhantomData<T>), }
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `E2` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `E2` representable
+   |
+LL | enum E2<T> { V2(Box<E2<E1>>, marker::PhantomData<T>), }
+   |                 ^^^^      ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-32326.stderr

@@ -8,7 +8,10 @@ LL |     Plus(Expr, Expr),
    |          |
    |          recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Expr` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Expr` representable
+   |
+LL |     Plus(Box<Expr>, Box<Expr>),
+   |          ^^^^    ^  ^^^^    ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-3779.stderr

@@ -5,9 +5,12 @@ LL | struct S {
    | ^^^^^^^^ recursive type has infinite size
 LL |
 LL |     element: Option<S>
-   |     ------------------ recursive without indirection
+   |              --------- recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `S` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `S` representable
+   |
+LL |     element: Box<Option<S>>
+   |              ^^^^         ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-57271.stderr

@@ -7,7 +7,10 @@ LL |     Class(ClassTypeSignature),
 LL |     Array(TypeSignature),
    |           ------------- recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `ObjectType` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `ObjectType` representable
+   |
+LL |     Array(Box<TypeSignature>),
+   |           ^^^^             ^
 
 error[E0072]: recursive type `TypeSignature` has infinite size
   --> $DIR/issue-57271.rs:19:1
@@ -18,7 +21,10 @@ LL |     Base(BaseType),
 LL |     Object(ObjectType),
    |            ---------- recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `TypeSignature` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `TypeSignature` representable
+   |
+LL |     Object(Box<ObjectType>),
+   |            ^^^^          ^
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-72554.stderr

@@ -6,7 +6,10 @@ LL | pub enum ElemDerived {
 LL |     A(ElemDerived)
    |       ----------- recursive without indirection
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `ElemDerived` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `ElemDerived` representable
+   |
+LL |     A(Box<ElemDerived>)
+   |       ^^^^           ^
 
 error: aborting due to previous error
 

src/test/ui/recursion/recursive-enum.stderr

@@ -6,7 +6,10 @@ LL | enum List<T> { Cons(T, List<T>), Nil }
    | |
    | recursive type has infinite size
    |
-   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `List` representable
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `List` representable
+   |
+LL | enum List<T> { Cons(T, Box<List<T>>), Nil }
+   |                        ^^^^       ^
 
 error: aborting due to previous error