Rollup merge of #122560 - jswrenn:not-yet-supported, r=compiler-errors

Safe Transmute: Use 'not yet supported', not 'unspecified' in errors

We can (and will) support analyzing the transmutability of types whose layouts aren't completely specified by its repr. This change ensures that the error messages remain sensible after this support lands.

r? ``@compiler-errors``

Author: matthiaskrgr

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

@@ -3073,29 +3073,29 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 let src = trait_ref.args.type_at(1);
                 let err_msg = format!("`{src}` cannot be safely transmuted into `{dst}`");
                 let safe_transmute_explanation = match reason {
-                    rustc_transmute::Reason::SrcIsUnspecified => {
-                        format!("`{src}` does not have a well-specified layout")
+                    rustc_transmute::Reason::SrcIsNotYetSupported => {
+                        format!("analyzing the transmutability of `{src}` is not yet supported.")
                     }
 
-                    rustc_transmute::Reason::DstIsUnspecified => {
-                        format!("`{dst}` does not have a well-specified layout")
+                    rustc_transmute::Reason::DstIsNotYetSupported => {
+                        format!("analyzing the transmutability of `{dst}` is not yet supported.")
                     }
 
                     rustc_transmute::Reason::DstIsBitIncompatible => {
-                        format!("At least one value of `{src}` isn't a bit-valid value of `{dst}`")
+                        format!("at least one value of `{src}` isn't a bit-valid value of `{dst}`")
                     }
 
                     rustc_transmute::Reason::DstMayHaveSafetyInvariants => {
                         format!("`{dst}` may carry safety invariants")
                     }
                     rustc_transmute::Reason::DstIsTooBig => {
-                        format!("The size of `{src}` is smaller than the size of `{dst}`")
+                        format!("the size of `{src}` is smaller than the size of `{dst}`")
                     }
                     rustc_transmute::Reason::DstRefIsTooBig { src, dst } => {
                         let src_size = src.size;
                         let dst_size = dst.size;
                         format!(
-                            "The referent size of `{src}` ({src_size} bytes) is smaller than that of `{dst}` ({dst_size} bytes)"
+                            "the referent size of `{src}` ({src_size} bytes) is smaller than that of `{dst}` ({dst_size} bytes)"
                         )
                     }
                     rustc_transmute::Reason::SrcSizeOverflow => {
@@ -3113,7 +3113,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         dst_min_align,
                     } => {
                         format!(
-                            "The minimum alignment of `{src}` ({src_min_align}) should be greater than that of `{dst}` ({dst_min_align})"
+                            "the minimum alignment of `{src}` ({src_min_align}) should be greater than that of `{dst}` ({dst_min_align})"
                         )
                     }
                     rustc_transmute::Reason::DstIsMoreUnique => {

compiler/rustc_transmute/src/layout/tree.rs

@@ -186,8 +186,8 @@ pub(crate) mod rustc {
 
     #[derive(Debug, Copy, Clone)]
     pub(crate) enum Err {
-        /// The layout of the type is unspecified.
-        Unspecified,
+        /// The layout of the type is not yet supported.
+        NotYetSupported,
         /// This error will be surfaced elsewhere by rustc, so don't surface it.
         UnknownLayout,
         /// Overflow size
@@ -288,14 +288,14 @@ pub(crate) mod rustc {
                     if members.len() == 0 {
                         Ok(Tree::unit())
                     } else {
-                        Err(Err::Unspecified)
+                        Err(Err::NotYetSupported)
                     }
                 }
 
                 ty::Array(ty, len) => {
                     let len = len
                         .try_eval_target_usize(tcx, ParamEnv::reveal_all())
-                        .ok_or(Err::Unspecified)?;
+                        .ok_or(Err::NotYetSupported)?;
                     let elt = Tree::from_ty(*ty, tcx)?;
                     Ok(std::iter::repeat(elt)
                         .take(len as usize)
@@ -307,7 +307,7 @@ pub(crate) mod rustc {
 
                     // If the layout is ill-specified, halt.
                     if !(adt_def.repr().c() || adt_def.repr().int.is_some()) {
-                        return Err(Err::Unspecified);
+                        return Err(Err::NotYetSupported);
                     }
 
                     // Compute a summary of the type's layout.
@@ -348,7 +348,7 @@ pub(crate) mod rustc {
                         AdtKind::Union => {
                             // is the layout well-defined?
                             if !adt_def.repr().c() {
-                                return Err(Err::Unspecified);
+                                return Err(Err::NotYetSupported);
                             }
 
                             let ty_layout = layout_of(tcx, ty)?;
@@ -384,7 +384,7 @@ pub(crate) mod rustc {
                     }))
                 }
 
-                _ => Err(Err::Unspecified),
+                _ => Err(Err::NotYetSupported),
             }
         }
 

compiler/rustc_transmute/src/lib.rs

@@ -43,10 +43,10 @@ pub enum Condition<R> {
 /// Answers "why wasn't the source type transmutable into the destination type?"
 #[derive(Debug, Hash, Eq, PartialEq, PartialOrd, Ord, Clone)]
 pub enum Reason<T> {
-    /// The layout of the source type is unspecified.
-    SrcIsUnspecified,
-    /// The layout of the destination type is unspecified.
-    DstIsUnspecified,
+    /// The layout of the source type is not yet supported.
+    SrcIsNotYetSupported,
+    /// The layout of the destination type is not yet supported.
+    DstIsNotYetSupported,
     /// The layout of the destination type is bit-incompatible with the source type.
     DstIsBitIncompatible,
     /// The destination type may carry safety invariants.

compiler/rustc_transmute/src/maybe_transmutable/mod.rs

@@ -56,8 +56,8 @@ mod rustc {
                 }
                 (Err(Err::UnknownLayout), _) => Answer::No(Reason::SrcLayoutUnknown),
                 (_, Err(Err::UnknownLayout)) => Answer::No(Reason::DstLayoutUnknown),
-                (Err(Err::Unspecified), _) => Answer::No(Reason::SrcIsUnspecified),
-                (_, Err(Err::Unspecified)) => Answer::No(Reason::DstIsUnspecified),
+                (Err(Err::NotYetSupported), _) => Answer::No(Reason::SrcIsNotYetSupported),
+                (_, Err(Err::NotYetSupported)) => Answer::No(Reason::DstIsNotYetSupported),
                 (Err(Err::SizeOverflow), _) => Answer::No(Reason::SrcSizeOverflow),
                 (_, Err(Err::SizeOverflow)) => Answer::No(Reason::DstSizeOverflow),
                 (Ok(src), Ok(dst)) => MaybeTransmutableQuery { src, dst, assume, context }.answer(),

tests/ui/transmutability/alignment/align-fail.stderr

@@ -2,7 +2,7 @@ error[E0277]: `&[u8; 0]` cannot be safely transmuted into `&[u16; 0]`
   --> $DIR/align-fail.rs:21:55
    |
 LL | ...tatic [u8; 0], &'static [u16; 0]>();
-   |                   ^^^^^^^^^^^^^^^^^ The minimum alignment of `&[u8; 0]` (1) should be greater than that of `&[u16; 0]` (2)
+   |                   ^^^^^^^^^^^^^^^^^ the minimum alignment of `&[u8; 0]` (1) should be greater than that of `&[u16; 0]` (2)
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/align-fail.rs:9:14

tests/ui/transmutability/arrays/should_require_well_defined_layout.stderr

@@ -2,7 +2,7 @@ error[E0277]: `[String; 0]` cannot be safely transmuted into `()`
   --> $DIR/should_require_well_defined_layout.rs:25:52
    |
 LL |         assert::is_maybe_transmutable::<repr_rust, ()>();
-   |                                                    ^^ `[String; 0]` does not have a well-specified layout
+   |                                                    ^^ analyzing the transmutability of `[String; 0]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14
@@ -23,7 +23,7 @@ error[E0277]: `u128` cannot be safely transmuted into `[String; 0]`
   --> $DIR/should_require_well_defined_layout.rs:26:47
    |
 LL |         assert::is_maybe_transmutable::<u128, repr_rust>();
-   |                                               ^^^^^^^^^ `[String; 0]` does not have a well-specified layout
+   |                                               ^^^^^^^^^ analyzing the transmutability of `[String; 0]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14
@@ -44,7 +44,7 @@ error[E0277]: `[String; 1]` cannot be safely transmuted into `()`
   --> $DIR/should_require_well_defined_layout.rs:31:52
    |
 LL |         assert::is_maybe_transmutable::<repr_rust, ()>();
-   |                                                    ^^ `[String; 1]` does not have a well-specified layout
+   |                                                    ^^ analyzing the transmutability of `[String; 1]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14
@@ -65,7 +65,7 @@ error[E0277]: `u128` cannot be safely transmuted into `[String; 1]`
   --> $DIR/should_require_well_defined_layout.rs:32:47
    |
 LL |         assert::is_maybe_transmutable::<u128, repr_rust>();
-   |                                               ^^^^^^^^^ `[String; 1]` does not have a well-specified layout
+   |                                               ^^^^^^^^^ analyzing the transmutability of `[String; 1]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14
@@ -86,7 +86,7 @@ error[E0277]: `[String; 2]` cannot be safely transmuted into `()`
   --> $DIR/should_require_well_defined_layout.rs:37:52
    |
 LL |         assert::is_maybe_transmutable::<repr_rust, ()>();
-   |                                                    ^^ `[String; 2]` does not have a well-specified layout
+   |                                                    ^^ analyzing the transmutability of `[String; 2]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14
@@ -107,7 +107,7 @@ error[E0277]: `u128` cannot be safely transmuted into `[String; 2]`
   --> $DIR/should_require_well_defined_layout.rs:38:47
    |
 LL |         assert::is_maybe_transmutable::<u128, repr_rust>();
-   |                                               ^^^^^^^^^ `[String; 2]` does not have a well-specified layout
+   |                                               ^^^^^^^^^ analyzing the transmutability of `[String; 2]` is not yet supported.
    |
 note: required by a bound in `is_maybe_transmutable`
   --> $DIR/should_require_well_defined_layout.rs:12:14