Add CoerceShared field-wise reborrow WF checks

compiler/rustc_hir_analysis/src/diagnostics.rs

@@ -1347,13 +1347,112 @@ pub(crate) struct CoerceSharedNotSingleLifetimeParam {
 }
 
 #[derive(Diagnostic)]
-#[diag("implementing `{$trait_name}` does not allow multiple lifetimes or fields to be coerced")]
+#[diag(
+    "implementing `{$trait_name}` requires exactly one lifetime argument in the reborrowed type"
+)]
 pub(crate) struct CoerceSharedMulti {
     #[primary_span]
     pub span: Span,
     pub trait_name: &'static str,
 }
 
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` requires source and target to use the same reborrow lifetime \
+     argument"
+)]
+pub(crate) struct CoerceSharedLifetimeMismatch {
+    #[primary_span]
+    pub span: Span,
+    #[label("source reborrow lifetime")]
+    pub source_lifetime_span: Option<Span>,
+    #[label("target reborrow lifetime")]
+    pub target_lifetime_span: Option<Span>,
+    pub trait_name: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` requires corresponding fields to match, \
+     be reborrowable with `CoerceShared`, or coerce a mutable reference field \
+     to a shared reference field"
+)]
+pub(crate) struct CoerceSharedFieldMismatch<'tcx> {
+    #[primary_span]
+    #[label("target field `{$target_name}` has type `{$target_ty}`")]
+    pub span: Span,
+    #[label("source field `{$source_name}` has type `{$source_ty}`")]
+    pub source_span: Span,
+    #[label("required by this `CoerceShared` implementation")]
+    pub impl_span: Span,
+    pub source_name: Symbol,
+    pub source_ty: Ty<'tcx>,
+    pub target_name: Symbol,
+    pub target_ty: Ty<'tcx>,
+    pub trait_name: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` requires every target field to have a corresponding source field"
+)]
+pub(crate) struct CoerceSharedMissingField {
+    #[primary_span]
+    #[label("target field `{$field_name}` has no corresponding source field")]
+    pub span: Span,
+    #[label("source type `{$source_ty_name}` does not contain field `{$field_name}`")]
+    pub source_ty_span: Span,
+    pub trait_name: &'static str,
+    pub source_ty_name: Symbol,
+    pub field_name: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` requires source and target structs to use the same field style"
+)]
+pub(crate) struct CoerceSharedFieldStyleMismatch {
+    #[primary_span]
+    pub span: Span,
+    pub trait_name: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` requires all {$role} type fields to be accessible from the impl"
+)]
+pub(crate) struct CoerceSharedInaccessibleField {
+    #[primary_span]
+    pub span: Span,
+    #[label("{$role} type `{$type_name}` has inaccessible reborrow data fields")]
+    pub type_span: Span,
+    pub trait_name: &'static str,
+    pub role: &'static str,
+    pub type_name: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(
+    "implementing `{$trait_name}` currently requires source and target to have at most one \
+     non-ZST reborrow data field"
+)]
+#[note(
+    "this is a temporary restriction until `CoerceShared` lowering supports non-trivially \
+     memcpy-compatible field layouts"
+)]
+pub(crate) struct CoerceSharedMultipleNonZstFields {
+    #[primary_span]
+    #[label("in this `CoerceShared` implementation")]
+    pub span: Span,
+    #[label("source type has {$source_count} non-ZST reborrow data fields")]
+    pub source_ty_span: Span,
+    #[label("target type has {$target_count} non-ZST reborrow data fields")]
+    pub target_ty_span: Span,
+    pub trait_name: &'static str,
+    pub source_count: usize,
+    pub target_count: usize,
+}
+
 #[derive(Diagnostic)]
 #[diag("the trait `{$trait_name}` may only be implemented for a coercion between structures", code = E0377)]
 pub(crate) struct CoerceUnsizedNonStruct {

tests/ui/reborrow/coerce-shared-associated-type-field.stderr

@@ -1,8 +1,14 @@
-error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
-  --> $DIR/coerce-shared-associated-type-field.rs:27:10
+error: implementing `CoerceShared` currently requires source and target to have at most one non-ZST reborrow data field
+  --> $DIR/coerce-shared-associated-type-field.rs:27:1
    |
 LL | impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
-   |          ^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^---------^^^^^^---------^^^
+   | |                     |              |
+   | |                     |              source type has 2 non-ZST reborrow data fields
+   | |                     target type has 2 non-ZST reborrow data fields
+   | in this `CoerceShared` implementation
+   |
+   = note: this is a temporary restriction until `CoerceShared` lowering supports non-trivially memcpy-compatible field layouts
 
 error: aborting due to 1 previous error
 

tests/ui/reborrow/coerce-shared-decl-macro-hygiene.stderr

@@ -1,12 +1,17 @@
-error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
-  --> $DIR/coerce-shared-decl-macro-hygiene.rs:20:14
+error: implementing `CoerceShared` currently requires source and target to have at most one non-ZST reborrow data field
+  --> $DIR/coerce-shared-decl-macro-hygiene.rs:20:5
    |
 LL |     impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
-   |              ^^^^^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^^^^---------^^^^^^---------^^^
+   |     |                     |              |
+   |     |                     |              source type has 2 non-ZST reborrow data fields
+   |     |                     target type has 2 non-ZST reborrow data fields
+   |     in this `CoerceShared` implementation
 ...
 LL | my_macro!(field);
    | ---------------- in this macro invocation
    |
+   = note: this is a temporary restriction until `CoerceShared` lowering supports non-trivially memcpy-compatible field layouts
    = note: this error originates in the macro `my_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error

tests/ui/reborrow/coerce-shared-field-lifetime-swap.rs

@@ -12,10 +12,10 @@ impl Reborrow for MyMut<'_> {}
 #[derive(Copy, Clone)]
 struct MyRef<'a> {
     x: &'a (),
+    //~^ ERROR
     y: &'static (),
 }
 
 impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
-//~^ ERROR
 
 fn main() {}

tests/ui/reborrow/coerce-shared-field-lifetime-swap.stderr

@@ -1,8 +1,14 @@
-error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
-  --> $DIR/coerce-shared-field-lifetime-swap.rs:18:10
+error: implementing `CoerceShared` requires corresponding fields to match, be reborrowable with `CoerceShared`, or coerce a mutable reference field to a shared reference field
+  --> $DIR/coerce-shared-field-lifetime-swap.rs:14:5
    |
+LL |     x: &'static (),
+   |     -------------- source field `x` has type `&'static ()`
+...
+LL |     x: &'a (),
+   |     ^^^^^^^^^ target field `x` has type `&'a ()`
+...
 LL | impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
-   |          ^^^^^^^^^^^^^^^^^^^^^^^
+   | ------------------------------------------------- required by this `CoerceShared` implementation
 
 error: aborting due to 1 previous error
 

tests/ui/reborrow/coerce-shared-field-relations.rs

@@ -24,6 +24,7 @@ impl<'a, T> Reborrow for RenamedMut<'a, T> {}
 #[derive(Clone, Copy)]
 struct RenamedRef<'a, T> {
     target: &'a T,
+    //~^ ERROR
 }
 
 impl<'a, T> CoerceShared<RenamedRef<'a, T>> for RenamedMut<'a, T> {}
@@ -37,11 +38,11 @@ impl<'a, T> Reborrow for BadMut<'a, T> {}
 #[derive(Clone, Copy)]
 struct BadRef<'a, T> {
     value: &'a u32,
+    //~^ ERROR
     _marker: std::marker::PhantomData<T>,
 }
 
 impl<'a, T> CoerceShared<BadRef<'a, T>> for BadMut<'a, T> {}
-//~^ ERROR
 
 fn good(_value: CustomRef<'_, u32>) {}
 

tests/ui/reborrow/coerce-shared-field-relations.stderr

@@ -1,9 +1,23 @@
-error[E0277]: the trait bound `&'a mut T: CoerceShared<&'a u32>` is not satisfied
-  --> $DIR/coerce-shared-field-relations.rs:43:1
+error: implementing `CoerceShared` requires every target field to have a corresponding source field
+  --> $DIR/coerce-shared-field-relations.rs:26:5
    |
+LL |     target: &'a T,
+   |     ^^^^^^^^^^^^^ target field `target` has no corresponding source field
+...
+LL | impl<'a, T> CoerceShared<RenamedRef<'a, T>> for RenamedMut<'a, T> {}
+   |                                                 ----------------- source type `RenamedMut` does not contain field `target`
+
+error: implementing `CoerceShared` requires corresponding fields to match, be reborrowable with `CoerceShared`, or coerce a mutable reference field to a shared reference field
+  --> $DIR/coerce-shared-field-relations.rs:40:5
+   |
+LL |     value: &'a mut T,
+   |     ---------------- source field `value` has type `&'a mut T`
+...
+LL |     value: &'a u32,
+   |     ^^^^^^^^^^^^^^ target field `value` has type `&'a u32`
+...
 LL | impl<'a, T> CoerceShared<BadRef<'a, T>> for BadMut<'a, T> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the nightly-only, unstable trait `CoerceShared<&'a u32>` is not implemented for `&'a mut T`
+   | ------------------------------------------------------------ required by this `CoerceShared` implementation
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.

tests/ui/reborrow/coerce-shared-foreign-private-field.rs

@@ -1,5 +1,3 @@
-//@ check-pass
-
 //@ aux-build: reborrow_foreign_private.rs
 
 #![feature(reborrow)]
@@ -16,5 +14,6 @@ struct LocalMut<'a> {
 impl<'a> Reborrow for LocalMut<'a> {}
 
 impl<'a> CoerceShared<ForeignRef<'a>> for LocalMut<'a> {}
+//~^ ERROR
 
 fn main() {}

tests/ui/reborrow/coerce-shared-foreign-private-field.stderr

@@ -0,0 +1,10 @@
+error: implementing `CoerceShared` requires all target type fields to be accessible from the impl
+  --> $DIR/coerce-shared-foreign-private-field.rs:16:1
+   |
+LL | impl<'a> CoerceShared<ForeignRef<'a>> for LocalMut<'a> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^--------------^^^^^^^^^^^^^^^^^^^^^
+   |                       |
+   |                       target type `ForeignRef` has inaccessible reborrow data fields
+
+error: aborting due to 1 previous error
+

tests/ui/reborrow/coerce-shared-foreign-private-tuple-field.rs

@@ -1,5 +1,3 @@
-//@ check-pass
-
 #![feature(reborrow)]
 
 use std::marker::{CoerceShared, PhantomData, Reborrow};
@@ -18,5 +16,6 @@ struct LocalPtrMut<'a>(*const i32, PhantomData<&'a ()>);
 impl<'a> Reborrow for LocalPtrMut<'a> {}
 
 impl<'a> CoerceShared<ForeignPtrRef<'a>> for LocalPtrMut<'a> {}
+//~^ ERROR
 
 fn main() {}

tests/ui/reborrow/coerce-shared-foreign-private-tuple-field.stderr

@@ -0,0 +1,10 @@
+error: implementing `CoerceShared` requires all target type fields to be accessible from the impl
+  --> $DIR/coerce-shared-foreign-private-tuple-field.rs:18:1
+   |
+LL | impl<'a> CoerceShared<ForeignPtrRef<'a>> for LocalPtrMut<'a> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
+   |                       |
+   |                       target type `ForeignPtrRef` has inaccessible reborrow data fields
+
+error: aborting due to 1 previous error
+

tests/ui/reborrow/coerce-shared-generics.stderr

@@ -1,8 +1,18 @@
-error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
-  --> $DIR/coerce-shared-generics.rs:26:38
+error: implementing `CoerceShared` currently requires source and target to have at most one non-ZST reborrow data field
+  --> $DIR/coerce-shared-generics.rs:26:1
    |
-LL | impl<'a, T, U: Copy, const N: usize> CoerceShared<BufferRef<'a, T, U, N>>
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |   impl<'a, T, U: Copy, const N: usize> CoerceShared<BufferRef<'a, T, U, N>>
+   |   ^                                                 ---------------------- target type has 2 non-ZST reborrow data fields
+   |  _|
+   | |
+LL | |
+LL | |     for BufferMut<'a, T, U, N>
+   | |         ---------------------- source type has 2 non-ZST reborrow data fields
+LL | | {
+LL | | }
+   | |_^ in this `CoerceShared` implementation
+   |
+   = note: this is a temporary restriction until `CoerceShared` lowering supports non-trivially memcpy-compatible field layouts
 
 error: aborting due to 1 previous error
 

tests/ui/reborrow/coerce-shared-lifetime-mismatch.rs

@@ -13,6 +13,7 @@ impl<'a> Reborrow for CustomMarker<'a> {}
 struct StaticMarkerRef<'a>(PhantomData<&'a ()>);
 
 impl<'a> CoerceShared<StaticMarkerRef<'static>> for CustomMarker<'a> {}
+//~^ ERROR
 
 fn method(_a: StaticMarkerRef<'static>) {}
 

tests/ui/reborrow/coerce-shared-lifetime-mismatch.stderr

@@ -1,5 +1,13 @@
+error: implementing `CoerceShared` requires source and target to use the same reborrow lifetime argument
+  --> $DIR/coerce-shared-lifetime-mismatch.rs:15:10
+   |
+LL | impl<'a> CoerceShared<StaticMarkerRef<'static>> for CustomMarker<'a> {}
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-------^^                  -- source reborrow lifetime
+   |                                       |
+   |                                       target reborrow lifetime
+
 error[E0597]: `a` does not live long enough
-  --> $DIR/coerce-shared-lifetime-mismatch.rs:21:12
+  --> $DIR/coerce-shared-lifetime-mismatch.rs:22:12
    |
 LL |     let a = CustomMarker(PhantomData);
    |         - binding `a` declared here
@@ -12,6 +20,6 @@ LL |
 LL | }
    | - `a` dropped here while still borrowed
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0597`.

tests/ui/reborrow/coerce-shared-missing-target-field.rs

@@ -12,9 +12,9 @@ impl<'a, T> Reborrow for MissingSourceMut<'a, T> {}
 struct MissingSourceRef<'a, T> {
     value: &'a T,
     len: usize,
+    //~^ ERROR
 }
 
 impl<'a, T> CoerceShared<MissingSourceRef<'a, T>> for MissingSourceMut<'a, T> {}
-//~^ ERROR
 
 fn main() {}

tests/ui/reborrow/coerce-shared-missing-target-field.stderr

@@ -1,8 +1,11 @@
-error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
-  --> $DIR/coerce-shared-missing-target-field.rs:17:13
+error: implementing `CoerceShared` requires every target field to have a corresponding source field
+  --> $DIR/coerce-shared-missing-target-field.rs:14:5
    |
+LL |     len: usize,
+   |     ^^^^^^^^^^ target field `len` has no corresponding source field
+...
 LL | impl<'a, T> CoerceShared<MissingSourceRef<'a, T>> for MissingSourceMut<'a, T> {}
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                       ----------------------- source type `MissingSourceMut` does not contain field `len`
 
 error: aborting due to 1 previous error
 

tests/ui/reborrow/coerce-shared-multi-non-zst.rs

@@ -0,0 +1,22 @@
+#![feature(reborrow)]
+#![allow(dead_code)]
+
+use std::marker::{CoerceShared, Reborrow};
+
+struct Source<'a> {
+    a: &'a mut u8,
+    b: u8,
+}
+
+#[derive(Copy, Clone)]
+struct Target<'a> {
+    a: &'a u8,
+    b: u8,
+}
+
+impl Reborrow for Source<'_> {}
+
+impl<'a> CoerceShared<Target<'a>> for Source<'a> {}
+//~^ ERROR
+
+fn main() {}

tests/ui/reborrow/coerce-shared-multi-non-zst.stderr

@@ -0,0 +1,14 @@
+error: implementing `CoerceShared` currently requires source and target to have at most one non-ZST reborrow data field
+  --> $DIR/coerce-shared-multi-non-zst.rs:19:1
+   |
+LL | impl<'a> CoerceShared<Target<'a>> for Source<'a> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^----------^^^^^^----------^^^
+   | |                     |               |
+   | |                     |               source type has 2 non-ZST reborrow data fields
+   | |                     target type has 2 non-ZST reborrow data fields
+   | in this `CoerceShared` implementation
+   |
+   = note: this is a temporary restriction until `CoerceShared` lowering supports non-trivially memcpy-compatible field layouts
+
+error: aborting due to 1 previous error
+