Remove the lifetime from DiagnosticArgValue.

Because it's almost always static.

This makes `impl IntoDiagnosticArg for DiagnosticArgValue` trivial,
which is nice.

There are a few diagnostics constructed in
`compiler/rustc_mir_build/src/check_unsafety.rs` and
`compiler/rustc_mir_transform/src/errors.rs` that now need symbols
converted to `String` with `to_string` instead of `&str` with `as_str`,
but that' no big deal, and worth it for the simplifications elsewhere.

compiler/rustc_middle/src/error.rs

@@ -95,17 +95,14 @@ pub(super) struct ConstNotUsedTraitAlias {
 
 pub struct CustomSubdiagnostic<'a> {
     pub msg: fn() -> DiagnosticMessage,
-    pub add_args:
-        Box<dyn FnOnce(&mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue<'static>)) + 'a>,
+    pub add_args: Box<dyn FnOnce(&mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue)) + 'a>,
 }
 
 impl<'a> CustomSubdiagnostic<'a> {
     pub fn label(x: fn() -> DiagnosticMessage) -> Self {
         Self::label_and_then(x, |_| {})
     }
-    pub fn label_and_then<
-        F: FnOnce(&mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue<'static>)) + 'a,
-    >(
+    pub fn label_and_then<F: FnOnce(&mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue)) + 'a>(
         msg: fn() -> DiagnosticMessage,
         f: F,
     ) -> Self {

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -233,7 +233,7 @@ pub enum InvalidMetaKind {
 }
 
 impl IntoDiagnosticArg for InvalidMetaKind {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         DiagnosticArgValue::Str(Cow::Borrowed(match self {
             InvalidMetaKind::SliceTooBig => "slice_too_big",
             InvalidMetaKind::TooBig => "too_big",
@@ -267,7 +267,7 @@ pub struct Misalignment {
 macro_rules! impl_into_diagnostic_arg_through_debug {
     ($($ty:ty),*$(,)?) => {$(
         impl IntoDiagnosticArg for $ty {
-            fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+            fn into_diagnostic_arg(self) -> DiagnosticArgValue {
                 DiagnosticArgValue::Str(Cow::Owned(format!("{self:?}")))
             }
         }
@@ -367,7 +367,7 @@ pub enum PointerKind {
 }
 
 impl IntoDiagnosticArg for PointerKind {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         DiagnosticArgValue::Str(
             match self {
                 Self::Ref => "ref",
@@ -485,10 +485,7 @@ pub trait MachineStopType: Any + fmt::Debug + Send {
     fn diagnostic_message(&self) -> DiagnosticMessage;
     /// Add diagnostic arguments by passing name and value pairs to `adder`, which are passed to
     /// fluent for formatting the translated diagnostic message.
-    fn add_args(
-        self: Box<Self>,
-        adder: &mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue<'static>),
-    );
+    fn add_args(self: Box<Self>, adder: &mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue));
 }
 
 impl dyn MachineStopType {

compiler/rustc_middle/src/mir/terminator.rs

@@ -292,7 +292,7 @@ impl<O> AssertKind<O> {
         }
     }
 
-    pub fn add_args(self, adder: &mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue<'static>))
+    pub fn add_args(self, adder: &mut dyn FnMut(Cow<'static, str>, DiagnosticArgValue))
     where
         O: fmt::Debug,
     {

compiler/rustc_middle/src/thir.rs

@@ -674,7 +674,7 @@ impl<'tcx> Pat<'tcx> {
 }
 
 impl<'tcx> IntoDiagnosticArg for Pat<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         format!("{self}").into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/consts/int.rs

@@ -117,7 +117,7 @@ impl std::fmt::Debug for ConstInt {
 impl IntoDiagnosticArg for ConstInt {
     // FIXME this simply uses the Debug impl, but we could probably do better by converting both
     // to an inherent method that returns `Cow`.
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         DiagnosticArgValue::Str(format!("{self:?}").into())
     }
 }

compiler/rustc_middle/src/ty/consts/kind.rs

@@ -15,7 +15,7 @@ pub struct UnevaluatedConst<'tcx> {
 }
 
 impl rustc_errors::IntoDiagnosticArg for UnevaluatedConst<'_> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue {
         format!("{self:?}").into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -20,7 +20,7 @@ use rustc_span::{BytePos, Span};
 use rustc_type_ir::TyKind::*;
 
 impl<'tcx> IntoDiagnosticArg for Ty<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/generic_args.rs

@@ -56,7 +56,7 @@ unsafe impl<'tcx> Sync for GenericArg<'tcx> where
 }
 
 impl<'tcx> IntoDiagnosticArg for GenericArg<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/layout.rs

@@ -269,7 +269,7 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
 }
 
 impl<'tcx> IntoDiagnosticArg for LayoutError<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -583,13 +583,13 @@ impl<'tcx> Predicate<'tcx> {
 }
 
 impl rustc_errors::IntoDiagnosticArg for Predicate<'_> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue {
         rustc_errors::DiagnosticArgValue::Str(std::borrow::Cow::Owned(self.to_string()))
     }
 }
 
 impl rustc_errors::IntoDiagnosticArg for Clause<'_> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue {
         rustc_errors::DiagnosticArgValue::Str(std::borrow::Cow::Owned(self.to_string()))
     }
 }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2632,7 +2632,7 @@ where
 pub struct TraitRefPrintOnlyTraitPath<'tcx>(ty::TraitRef<'tcx>);
 
 impl<'tcx> rustc_errors::IntoDiagnosticArg for TraitRefPrintOnlyTraitPath<'tcx> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }
@@ -2649,7 +2649,7 @@ impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitPath<'tcx> {
 pub struct TraitRefPrintSugared<'tcx>(ty::TraitRef<'tcx>);
 
 impl<'tcx> rustc_errors::IntoDiagnosticArg for TraitRefPrintSugared<'tcx> {
-    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }

compiler/rustc_middle/src/ty/sty.rs

@@ -862,7 +862,7 @@ impl<'tcx> PolyTraitRef<'tcx> {
 }
 
 impl<'tcx> IntoDiagnosticArg for TraitRef<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }
@@ -908,7 +908,7 @@ impl<'tcx> ExistentialTraitRef<'tcx> {
 }
 
 impl<'tcx> IntoDiagnosticArg for ExistentialTraitRef<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }
@@ -1149,7 +1149,7 @@ impl<'tcx, T> IntoDiagnosticArg for Binder<'tcx, T>
 where
     T: IntoDiagnosticArg,
 {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.value.into_diagnostic_arg()
     }
 }
@@ -1359,7 +1359,7 @@ impl<'tcx> FnSig<'tcx> {
 }
 
 impl<'tcx> IntoDiagnosticArg for FnSig<'tcx> {
-    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue {
         self.to_string().into_diagnostic_arg()
     }
 }