compiler: remove string-specific ABI errors

These are either residue of a long-term migration away from something,
or are simply trying too hard to be specifically useful:
nearest-match suggestions for ABI strings should handle this.

compiler/rustc_abi/src/extern_abi.rs

@@ -141,27 +141,14 @@ pub const AbiDatas: &[AbiData] = &[
 ];
 
 #[derive(Copy, Clone, Debug)]
-pub enum AbiUnsupported {
-    Unrecognized,
-    Reason { explain: &'static str },
-}
-
+pub struct AbiUnsupported {}
 /// Returns the ABI with the given name (if any).
 pub fn lookup(name: &str) -> Result<Abi, AbiUnsupported> {
-    AbiDatas.iter().find(|abi_data| name == abi_data.name).map(|&x| x.abi).ok_or_else(|| match name {
-        "riscv-interrupt" => AbiUnsupported::Reason {
-            explain: "please use one of riscv-interrupt-m or riscv-interrupt-s for machine- or supervisor-level interrupts, respectively",
-        },
-        "riscv-interrupt-u" => AbiUnsupported::Reason {
-            explain: "user-mode interrupt handlers have been removed from LLVM pending standardization, see: https://reviews.llvm.org/D149314",
-        },
-        "wasm" => AbiUnsupported::Reason {
-            explain: "non-standard wasm ABI is no longer supported",
-        },
-
-        _ => AbiUnsupported::Unrecognized,
-
-    })
+    AbiDatas
+        .iter()
+        .find(|abi_data| name == abi_data.name)
+        .map(|&x| x.abi)
+        .ok_or_else(|| AbiUnsupported {})
 }
 
 pub fn all_names() -> Vec<&'static str> {

compiler/rustc_abi/src/extern_abi/tests.rs

@@ -18,7 +18,7 @@ fn lookup_cdecl() {
 #[test]
 fn lookup_baz() {
     let abi = lookup("baz");
-    assert_matches!(abi, Err(AbiUnsupported::Unrecognized));
+    assert_matches!(abi, Err(AbiUnsupported {}));
 }
 
 #[test]

compiler/rustc_ast_lowering/src/errors.rs

@@ -1,5 +1,5 @@
+use rustc_errors::DiagArgFromDisplay;
 use rustc_errors::codes::*;
-use rustc_errors::{Diag, DiagArgFromDisplay, EmissionGuarantee, SubdiagMessageOp, Subdiagnostic};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Ident, Span, Symbol};
 
@@ -32,8 +32,6 @@ pub(crate) struct InvalidAbi {
     pub abi: Symbol,
     pub command: String,
     #[subdiagnostic]
-    pub explain: Option<InvalidAbiReason>,
-    #[subdiagnostic]
     pub suggestion: Option<InvalidAbiSuggestion>,
 }
 
@@ -45,19 +43,6 @@ pub(crate) struct TupleStructWithDefault {
     pub span: Span,
 }
 
-pub(crate) struct InvalidAbiReason(pub &'static str);
-
-impl Subdiagnostic for InvalidAbiReason {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _: &F,
-    ) {
-        #[allow(rustc::untranslatable_diagnostic)]
-        diag.note(self.0);
-    }
-}
-
 #[derive(Subdiagnostic)]
 #[suggestion(
     ast_lowering_invalid_abi_suggestion,

compiler/rustc_ast_lowering/src/item.rs

@@ -17,8 +17,7 @@ use thin_vec::ThinVec;
 use tracing::instrument;
 
 use super::errors::{
-    InvalidAbi, InvalidAbiReason, InvalidAbiSuggestion, MisplacedRelaxTraitBound,
-    TupleStructWithDefault,
+    InvalidAbi, InvalidAbiSuggestion, MisplacedRelaxTraitBound, TupleStructWithDefault,
 };
 use super::stability::{enabled_names, gate_unstable_abi};
 use super::{
@@ -1388,8 +1387,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     pub(super) fn lower_abi(&mut self, abi_str: StrLit) -> ExternAbi {
         let ast::StrLit { symbol_unescaped, span, .. } = abi_str;
-        let extern_abi = rustc_abi::lookup(symbol_unescaped.as_str()).unwrap_or_else(|err| {
-            self.error_on_invalid_abi(abi_str, err);
+        let extern_abi = rustc_abi::lookup(symbol_unescaped.as_str()).unwrap_or_else(|_| {
+            self.error_on_invalid_abi(abi_str);
             ExternAbi::Rust
         });
         let sess = self.tcx.sess;
@@ -1406,7 +1405,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    fn error_on_invalid_abi(&self, abi: StrLit, err: rustc_abi::AbiUnsupported) {
+    fn error_on_invalid_abi(&self, abi: StrLit) {
         let abi_names = enabled_names(self.tcx.features(), abi.span)
             .iter()
             .map(|s| Symbol::intern(s))
@@ -1415,10 +1414,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.dcx().emit_err(InvalidAbi {
             abi: abi.symbol_unescaped,
             span: abi.span,
-            explain: match err {
-                rustc_abi::AbiUnsupported::Reason { explain } => Some(InvalidAbiReason(explain)),
-                _ => None,
-            },
             suggestion: suggested_name.map(|suggested_name| InvalidAbiSuggestion {
                 span: abi.span,
                 suggestion: format!("\"{suggested_name}\""),