Migrate "constant pattern depends on generic parameter" diagnostic

Author: lzcunt

compiler/rustc_error_messages/locales/en-US/mir_build.ftl

@@ -195,3 +195,6 @@ mir_build_non_const_path = runtime values cannot be referenced in patterns
 mir_build_unreachable_pattern = unreachable pattern
     .label = unreachable pattern
     .catchall_label = matches any value
+
+mir_build_const_pattern_depends_on_generic_parameter =
+    constant pattern depends on a generic parameter

compiler/rustc_mir_build/src/errors.rs

@@ -466,3 +466,10 @@ pub struct UnreachablePattern {
     #[label(mir_build::catchall_label)]
     pub catchall: Option<Span>,
 }
+
+#[derive(SessionDiagnostic)]
+#[diag(mir_build::const_pattern_depends_on_generic_parameter)]
+pub struct ConstPatternDependsOnGenericParameter {
+    #[primary_span]
+    pub span: Span,
+}

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -8,6 +8,7 @@ mod usefulness;
 pub(crate) use self::check_match::check_match;
 pub(crate) use self::usefulness::MatchCheckCtxt;
 
+use crate::errors::ConstPatternDependsOnGenericParameter;
 use crate::thir::util::UserAnnotatedTyHelpers;
 
 use rustc_errors::struct_span_err;
@@ -530,7 +531,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             Err(ErrorHandled::TooGeneric) => {
                 // While `Reported | Linted` cases will have diagnostics emitted already
                 // it is not true for TooGeneric case, so we need to give user more information.
-                self.tcx.sess.span_err(span, "constant pattern depends on a generic parameter");
+                self.tcx.sess.emit_err(ConstPatternDependsOnGenericParameter { span });
                 pat_from_kind(PatKind::Wild)
             }
             Err(_) => {
@@ -562,9 +563,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     }
                     ConstKind::Unevaluated(_) => {
                         // If we land here it means the const can't be evaluated because it's `TooGeneric`.
-                        self.tcx
-                            .sess
-                            .span_err(span, "constant pattern depends on a generic parameter");
+                        self.tcx.sess.emit_err(ConstPatternDependsOnGenericParameter { span });
                         return PatKind::Wild;
                     }
                     _ => bug!("Expected either ConstKind::Param or ConstKind::Unevaluated"),