Maintain a list of types permitted per pattern

compiler/rustc_hir_analysis/src/errors/pattern_types.rs

@@ -1,4 +1,5 @@
 use rustc_macros::Diagnostic;
+use rustc_middle::ty::Ty;
 use rustc_span::Span;
 
 #[derive(Diagnostic)]
@@ -7,3 +8,14 @@ pub(crate) struct WildPatTy {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_invalid_base_type)]
+pub(crate) struct InvalidBaseType<'tcx> {
+    pub ty: Ty<'tcx>,
+    #[primary_span]
+    pub ty_span: Span,
+    pub pat: &'static str,
+    #[note]
+    pub pat_span: Span,
+}