Rollup merge of #91416 - compiler-errors:infinite-ty-option-box, r=estebank

Specialize infinite-type "insert some indirection" suggestion for Option

Suggest `Option<Box<_>>` instead of `Box<Option<_>>` for infinitely-recursive members of a struct.

Not sure if I can get the span of the generic subty of the Option so I can make this a `+++`-style suggestion. The current output is a tiny bit less fancy looking than the original suggestion.

Should I limit the specialization to just `Option<Box<TheOuterStruct>>`? Because right now it applies to all `Option` members in the struct that are returned by `Representability::SelfRecursive`.

Fixes #91402

r? `@estebank`
(since you wrote the original suggestion and are definitely most familiar with it!)

13 files changed, 160 insertions, 28 deletions

diff --git a/src/test/ui/issues/issue-17431-1.stderr b/src/test/ui/issues/issue-17431-1.stderr
index 4d739a3823b..db32eb952ba 100644
--- a/src/test/ui/issues/issue-17431-1.stderr
+++ b/src/test/ui/issues/issue-17431-1.stderr
@@ -8,8 +8,8 @@ LL | struct Foo { foo: Option<Option<Foo>> }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
    |
-LL | struct Foo { foo: Box<Option<Option<Foo>>> }
-   |                   ++++                   +
+LL | struct Foo { foo: Option<Box<Option<Foo>>> }
+   |                          ++++           +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-17431-2.stderr b/src/test/ui/issues/issue-17431-2.stderr
index e53134c5238..d23fd1474ac 100644
--- a/src/test/ui/issues/issue-17431-2.stderr
+++ b/src/test/ui/issues/issue-17431-2.stderr
@@ -8,8 +8,8 @@ LL | struct Baz { q: Option<Foo> }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Baz` representable
    |
-LL | struct Baz { q: Box<Option<Foo>> }
-   |                 ++++           +
+LL | struct Baz { q: Option<Box<Foo>> }
+   |                        ++++   +
 
 error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/issue-17431-2.rs:4:1
@@ -21,8 +21,8 @@ LL | struct Foo { q: Option<Baz> }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
    |
-LL | struct Foo { q: Box<Option<Baz>> }
-   |                 ++++           +
+LL | struct Foo { q: Option<Box<Baz>> }
+   |                        ++++   +
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-17431-4.stderr b/src/test/ui/issues/issue-17431-4.stderr
index f5aeeec7337..ddf669b8fd1 100644
--- a/src/test/ui/issues/issue-17431-4.stderr
+++ b/src/test/ui/issues/issue-17431-4.stderr
@@ -8,8 +8,8 @@ LL | struct Foo<T> { foo: Option<Option<Foo<T>>>, marker: marker::PhantomData<T>
    |
 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> }
-   |                      ++++                      +
+LL | struct Foo<T> { foo: Option<Box<Option<Foo<T>>>>, marker: marker::PhantomData<T> }
+   |                             ++++              +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-17431-7.stderr b/src/test/ui/issues/issue-17431-7.stderr
index aeaadaa6917..6f8a7e3867b 100644
--- a/src/test/ui/issues/issue-17431-7.stderr
+++ b/src/test/ui/issues/issue-17431-7.stderr
@@ -8,8 +8,8 @@ LL | enum Foo { Voo(Option<Option<Foo>>) }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
    |
-LL | enum Foo { Voo(Box<Option<Option<Foo>>>) }
-   |                ++++                   +
+LL | enum Foo { Voo(Option<Box<Option<Foo>>>) }
+   |                       ++++           +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-3779.stderr b/src/test/ui/issues/issue-3779.stderr
index 6a21472848a..e853d0f8c89 100644
--- a/src/test/ui/issues/issue-3779.stderr
+++ b/src/test/ui/issues/issue-3779.stderr
@@ -9,8 +9,8 @@ LL |     element: Option<S>
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `S` representable
    |
-LL |     element: Box<Option<S>>
-   |              ++++         +
+LL |     element: Option<Box<S>>
+   |                     ++++ +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/sized-cycle-note.stderr b/src/test/ui/sized-cycle-note.stderr
index 0726b16a919..536510814c5 100644
--- a/src/test/ui/sized-cycle-note.stderr
+++ b/src/test/ui/sized-cycle-note.stderr
@@ -8,8 +8,8 @@ LL | struct Baz { q: Option<Foo> }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Baz` representable
    |
-LL | struct Baz { q: Box<Option<Foo>> }
-   |                 ++++           +
+LL | struct Baz { q: Option<Box<Foo>> }
+   |                        ++++   +
 
 error[E0072]: recursive type `Foo` has infinite size
   --> $DIR/sized-cycle-note.rs:11:1
@@ -21,8 +21,8 @@ LL | struct Foo { q: Option<Baz> }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
    |
-LL | struct Foo { q: Box<Option<Baz>> }
-   |                 ++++           +
+LL | struct Foo { q: Option<Box<Baz>> }
+   |                        ++++   +
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/span/E0072.stderr b/src/test/ui/span/E0072.stderr
index 98e92751360..882ed577cf3 100644
--- a/src/test/ui/span/E0072.stderr
+++ b/src/test/ui/span/E0072.stderr
@@ -9,8 +9,8 @@ LL |     tail: Option<ListNode>,
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `ListNode` representable
    |
-LL |     tail: Box<Option<ListNode>>,
-   |           ++++                +
+LL |     tail: Option<Box<ListNode>>,
+   |                  ++++        +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/span/multiline-span-E0072.stderr b/src/test/ui/span/multiline-span-E0072.stderr
index cb71a55b09e..acfc60b51f3 100644
--- a/src/test/ui/span/multiline-span-E0072.stderr
+++ b/src/test/ui/span/multiline-span-E0072.stderr
@@ -12,8 +12,8 @@ LL | | }
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `ListNode` representable
    |
-LL |     tail: Box<Option<ListNode>>,
-   |           ++++                +
+LL |     tail: Option<Box<ListNode>>,
+   |                  ++++        +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/structs-enums/struct-rec/mutual-struct-recursion.stderr b/src/test/ui/structs-enums/struct-rec/mutual-struct-recursion.stderr
index c6d2434e424..80a494f3f65 100644
--- a/src/test/ui/structs-enums/struct-rec/mutual-struct-recursion.stderr
+++ b/src/test/ui/structs-enums/struct-rec/mutual-struct-recursion.stderr
@@ -37,8 +37,8 @@ LL |     y: Option<Option<D<T>>>,
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `C` representable
    |
-LL |     y: Box<Option<Option<D<T>>>>,
-   |        ++++                    +
+LL |     y: Option<Box<Option<D<T>>>>,
+   |               ++++            +
 
 error[E0072]: recursive type `D` has infinite size
   --> $DIR/mutual-struct-recursion.rs:18:1
@@ -51,8 +51,8 @@ LL |     z: Option<Option<C<T>>>,
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `D` representable
    |
-LL |     z: Box<Option<Option<C<T>>>>,
-   |        ++++                    +
+LL |     z: Option<Box<Option<C<T>>>>,
+   |               ++++            +
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/type/type-recursive-box-shadowed.rs b/src/test/ui/type/type-recursive-box-shadowed.rs
new file mode 100644
index 00000000000..e141c2149ff
--- /dev/null
+++ b/src/test/ui/type/type-recursive-box-shadowed.rs
@@ -0,0 +1,12 @@
+//FIXME(compiler-errors): This fixup should suggest the full box path, not just `Box`
+
+struct Box<T> {
+    t: T,
+}
+
+struct Foo {
+    //~^ ERROR recursive type `Foo` has infinite size
+    inner: Foo,
+}
+
+fn main() {}
diff --git a/src/test/ui/type/type-recursive-box-shadowed.stderr b/src/test/ui/type/type-recursive-box-shadowed.stderr
new file mode 100644
index 00000000000..c22d848f379
--- /dev/null
+++ b/src/test/ui/type/type-recursive-box-shadowed.stderr
@@ -0,0 +1,17 @@
+error[E0072]: recursive type `Foo` has infinite size
+  --> $DIR/type-recursive-box-shadowed.rs:7:1
+   |
+LL | struct Foo {
+   | ^^^^^^^^^^ recursive type has infinite size
+LL |
+LL |     inner: Foo,
+   |            --- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
+   |
+LL |     inner: Box<Foo>,
+   |            ++++   +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0072`.
diff --git a/src/test/ui/type/type-recursive.rs b/src/test/ui/type/type-recursive.rs
index 8558f761ee8..e8084f0d082 100644
--- a/src/test/ui/type/type-recursive.rs
+++ b/src/test/ui/type/type-recursive.rs
@@ -1,6 +1,30 @@
 struct T1 { //~ ERROR E0072
     foo: isize,
-    foolish: T1
+    foolish: T1,
+}
+
+struct T2 { //~ ERROR E0072
+    inner: Option<T2>,
+}
+
+type OptionT3 = Option<T3>;
+
+struct T3 { //~ ERROR E0072
+    inner: OptionT3,
+}
+
+struct T4(Option<T4>); //~ ERROR E0072
+
+enum T5 { //~ ERROR E0072
+    Variant(Option<T5>),
+}
+
+enum T6 { //~ ERROR E0072
+    Variant{ field: Option<T6> },
+}
+
+struct T7 { //~ ERROR E0072
+    foo: std::cell::Cell<Option<T7>>,
 }
 
 fn main() { }
diff --git a/src/test/ui/type/type-recursive.stderr b/src/test/ui/type/type-recursive.stderr
index 5a94a0fd683..04392f7390d 100644
--- a/src/test/ui/type/type-recursive.stderr
+++ b/src/test/ui/type/type-recursive.stderr
@@ -4,14 +4,93 @@ error[E0072]: recursive type `T1` has infinite size
 LL | struct T1 {
    | ^^^^^^^^^ recursive type has infinite size
 LL |     foo: isize,
-LL |     foolish: T1
+LL |     foolish: T1,
    |              -- recursive without indirection
    |
 help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T1` representable
    |
-LL |     foolish: Box<T1>
+LL |     foolish: Box<T1>,
    |              ++++  +
 
-error: aborting due to previous error
+error[E0072]: recursive type `T2` has infinite size
+  --> $DIR/type-recursive.rs:6:1
+   |
+LL | struct T2 {
+   | ^^^^^^^^^ recursive type has infinite size
+LL |     inner: Option<T2>,
+   |            ---------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T2` representable
+   |
+LL |     inner: Option<Box<T2>>,
+   |                   ++++  +
+
+error[E0072]: recursive type `T3` has infinite size
+  --> $DIR/type-recursive.rs:12:1
+   |
+LL | struct T3 {
+   | ^^^^^^^^^ recursive type has infinite size
+LL |     inner: OptionT3,
+   |            -------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T3` representable
+   |
+LL |     inner: Box<OptionT3>,
+   |            ++++        +
+
+error[E0072]: recursive type `T4` has infinite size
+  --> $DIR/type-recursive.rs:16:1
+   |
+LL | struct T4(Option<T4>);
+   | ^^^^^^^^^^----------^^
+   | |         |
+   | |         recursive without indirection
+   | recursive type has infinite size
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T4` representable
+   |
+LL | struct T4(Option<Box<T4>>);
+   |                  ++++  +
+
+error[E0072]: recursive type `T5` has infinite size
+  --> $DIR/type-recursive.rs:18:1
+   |
+LL | enum T5 {
+   | ^^^^^^^ recursive type has infinite size
+LL |     Variant(Option<T5>),
+   |             ---------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T5` representable
+   |
+LL |     Variant(Option<Box<T5>>),
+   |                    ++++  +
+
+error[E0072]: recursive type `T6` has infinite size
+  --> $DIR/type-recursive.rs:22:1
+   |
+LL | enum T6 {
+   | ^^^^^^^ recursive type has infinite size
+LL |     Variant{ field: Option<T6> },
+   |                     ---------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T6` representable
+   |
+LL |     Variant{ field: Option<Box<T6>> },
+   |                            ++++  +
+
+error[E0072]: recursive type `T7` has infinite size
+  --> $DIR/type-recursive.rs:26:1
+   |
+LL | struct T7 {
+   | ^^^^^^^^^ recursive type has infinite size
+LL |     foo: std::cell::Cell<Option<T7>>,
+   |          --------------------------- recursive without indirection
+   |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `T7` representable
+   |
+LL |     foo: Box<std::cell::Cell<Option<T7>>>,
+   |          ++++                           +
+
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0072`.