Avoid &format("...") calls in error message code.

Error message all end up passing into a function as an `impl
Into<{D,Subd}iagnosticMessage>`. If an error message is creatd as
`&format("...")` that means we allocate a string (in the `format!`
call), then take a reference, and then clone (allocating again) the
reference to produce the `{D,Subd}iagnosticMessage`, which is silly.

This commit removes the leading `&` from a lot of these cases. This
means the original `String` is moved into the
`{D,Subd}iagnosticMessage`, avoiding the double allocations. This
requires changing some function argument types from `&str` to `String`
(when all arguments are `String`) or `impl
Into<{D,Subd}iagnosticMessage>` (when some arguments are `String` and
some are `&str`).

compiler/rustc_middle/src/ty/context.rs

@@ -702,7 +702,11 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Constructs a `TyKind::Error` type and registers a `delay_span_bug` with the given `msg` to
     /// ensure it gets used.
     #[track_caller]
-    pub fn ty_error_with_message<S: Into<MultiSpan>>(self, span: S, msg: &str) -> Ty<'tcx> {
+    pub fn ty_error_with_message<S: Into<MultiSpan>>(
+        self,
+        span: S,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> Ty<'tcx> {
         let reported = self.sess.delay_span_bug(span, msg);
         self.mk_ty_from_kind(Error(reported))
     }
@@ -2435,7 +2439,7 @@ impl<'tcx> TyCtxtAt<'tcx> {
     /// Constructs a `TyKind::Error` type and registers a `delay_span_bug` with the given `msg` to
     /// ensure it gets used.
     #[track_caller]
-    pub fn ty_error_with_message(self, msg: &str) -> Ty<'tcx> {
+    pub fn ty_error_with_message(self, msg: impl Into<DiagnosticMessage>) -> Ty<'tcx> {
         self.tcx.ty_error_with_message(self.span, msg)
     }
 }

compiler/rustc_middle/src/ty/layout.rs

@@ -268,7 +268,7 @@ pub struct LayoutCx<'tcx, C> {
 impl<'tcx> LayoutCalculator for LayoutCx<'tcx, TyCtxt<'tcx>> {
     type TargetDataLayoutRef = &'tcx TargetDataLayout;
 
-    fn delay_bug(&self, txt: &str) {
+    fn delay_bug(&self, txt: String) {
         self.tcx.sess.delay_span_bug(DUMMY_SP, txt);
     }