Migrate "could not evaluate const pattern" diagnostic

Author: lzcunt

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

@@ -198,3 +198,5 @@ mir_build_unreachable_pattern = unreachable pattern
 
 mir_build_const_pattern_depends_on_generic_parameter =
     constant pattern depends on a generic parameter
+
+mir_build_could_not_eval_const_pattern = could not evaluate constant pattern

compiler/rustc_mir_build/src/errors.rs

@@ -473,3 +473,10 @@ pub struct ConstPatternDependsOnGenericParameter {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(SessionDiagnostic)]
+#[diag(mir_build::could_not_eval_const_pattern)]
+pub struct CouldNotEvalConstPattern {
+    #[primary_span]
+    pub span: Span,
+}

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

@@ -8,7 +8,7 @@ mod usefulness;
 pub(crate) use self::check_match::check_match;
 pub(crate) use self::usefulness::MatchCheckCtxt;
 
-use crate::errors::ConstPatternDependsOnGenericParameter;
+use crate::errors::*;
 use crate::thir::util::UserAnnotatedTyHelpers;
 
 use rustc_errors::struct_span_err;
@@ -503,7 +503,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             }
 
             Err(_) => {
-                self.tcx.sess.span_err(span, "could not evaluate constant pattern");
+                self.tcx.sess.emit_err(CouldNotEvalConstPattern { span });
                 return pat_from_kind(PatKind::Wild);
             }
         };
@@ -554,7 +554,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                 pat_from_kind(PatKind::Wild)
             }
             Err(_) => {
-                self.tcx.sess.span_err(span, "could not evaluate constant pattern");
+                self.tcx.sess.emit_err(CouldNotEvalConstPattern { span });
                 pat_from_kind(PatKind::Wild)
             }
         }