Make E0529 a structured error

Author: estebank

compiler/rustc_hir_typeck/messages.ftl

@@ -10,6 +10,7 @@ hir_typeck_address_of_temporary_taken = cannot take address of a temporary
 hir_typeck_arg_mismatch_indeterminate = argument type mismatch was detected, but rustc had trouble determining where
     .note = we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new
 
+hir_typeck_as_deref_suggestion = consider using `as_deref` here
 hir_typeck_base_expression_double_dot = base expression required after `..`
 hir_typeck_base_expression_double_dot_add_expr = add a base expression here
 hir_typeck_base_expression_double_dot_enable_default_field_values =
@@ -72,6 +73,9 @@ hir_typeck_dependency_on_unit_never_type_fallback = this function depends on nev
 
 hir_typeck_deref_is_empty = this expression `Deref`s to `{$deref_ty}` which implements `is_empty`
 
+hir_typeck_expected_array_or_slice = expected an array or slice, found `{$ty}`
+hir_typeck_expected_array_or_slice_label = pattern cannot match with input type `{$ty}`
+
 hir_typeck_expected_default_return_type = expected `()` because of default return type
 
 hir_typeck_expected_return_type = expected `{$expected}` because of return type
@@ -187,6 +191,8 @@ hir_typeck_self_ctor_from_outer_item = can't reference `Self` constructor from o
     .label = the inner item doesn't inherit generics from this impl, so `Self` is invalid to reference
     .suggestion = replace `Self` with the actual type
 
+hir_typeck_slicing_suggestion = consider slicing here
+
 hir_typeck_struct_expr_non_exhaustive =
     cannot create non-exhaustive {$what} using struct expression
 

compiler/rustc_hir_typeck/src/errors.rs

@@ -454,6 +454,44 @@ impl HelpUseLatestEdition {
     }
 }
 
+#[derive(Diagnostic)]
+#[diag(hir_typeck_expected_array_or_slice, code = E0529)]
+pub(crate) struct ExpectedArrayOrSlice<'tcx> {
+    #[primary_span]
+    #[label(hir_typeck_expected_array_or_slice_label)]
+    pub(crate) span: Span,
+    pub(crate) ty: Ty<'tcx>,
+    pub(crate) slice_pat_semantics: bool,
+    #[subdiagnostic]
+    pub(crate) as_deref: Option<AsDerefSuggestion>,
+    #[subdiagnostic]
+    pub(crate) slicing: Option<SlicingSuggestion>,
+}
+
+#[derive(Subdiagnostic)]
+#[suggestion(
+    hir_typeck_as_deref_suggestion,
+    code = ".as_deref()",
+    style = "verbose",
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct AsDerefSuggestion {
+    #[primary_span]
+    pub(crate) span: Span,
+}
+
+#[derive(Subdiagnostic)]
+#[suggestion(
+    hir_typeck_slicing_suggestion,
+    code = "[..]",
+    style = "verbose",
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct SlicingSuggestion {
+    #[primary_span]
+    pub(crate) span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_typeck_invalid_callee, code = E0618)]
 pub(crate) struct InvalidCallee<'tcx> {

compiler/rustc_hir_typeck/src/pat.rs

@@ -2712,16 +2712,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> ErrorGuaranteed {
         let PatInfo { top_info: ti, current_depth, .. } = pat_info;
 
-        let mut err = struct_span_code_err!(
-            self.dcx(),
-            span,
-            E0529,
-            "expected an array or slice, found `{expected_ty}`"
-        );
+        let mut slice_pat_semantics = false;
+        let mut as_deref = None;
+        let mut slicing = None;
         if let ty::Ref(_, ty, _) = expected_ty.kind()
             && let ty::Array(..) | ty::Slice(..) = ty.kind()
         {
-            err.help("the semantics of slice patterns changed recently; see issue #62254");
+            slice_pat_semantics = true;
         } else if self
             .autoderef(span, expected_ty)
             .silence_errors()
@@ -2738,28 +2735,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
                 {
                     // Slicing won't work here, but `.as_deref()` might (issue #91328).
-                    err.span_suggestion_verbose(
-                        span.shrink_to_hi(),
-                        "consider using `as_deref` here",
-                        ".as_deref()",
-                        Applicability::MaybeIncorrect,
-                    );
+                    as_deref = Some(errors::AsDerefSuggestion { span: span.shrink_to_hi() });
                 }
                 _ => (),
             }
 
             let is_top_level = current_depth <= 1;
             if is_slice_or_array_or_vector && is_top_level {
-                err.span_suggestion_verbose(
-                    span.shrink_to_hi(),
-                    "consider slicing here",
-                    "[..]",
-                    Applicability::MachineApplicable,
-                );
+                slicing = Some(errors::SlicingSuggestion { span: span.shrink_to_hi() });
             }
         }
-        err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
-        err.emit()
+        self.dcx().emit_err(errors::ExpectedArrayOrSlice {
+            span,
+            ty: expected_ty,
+            slice_pat_semantics,
+            as_deref,
+            slicing,
+        })
     }
 
     fn is_slice_or_array_or_vector(&self, ty: Ty<'tcx>) -> (bool, Ty<'tcx>) {

tests/ui/diagnostic-width/long-E0529.rs

@@ -7,8 +7,8 @@ type C = (B, B, B, B);
 type D = (C, C, C, C);
 
 fn foo(x: D) {
-    let [] = x; //~ ERROR expected an array or slice, found `(
-    //~^ pattern cannot match with input type `(
+    let [] = x; //~ ERROR expected an array or slice, found `(...
+    //~^ pattern cannot match with input type `(...
 }
 
 fn main() {}

tests/ui/diagnostic-width/long-E0529.stderr

@@ -1,8 +1,11 @@
-error[E0529]: expected an array or slice, found `((((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))))`
+error[E0529]: expected an array or slice, found `(..., ..., ..., ...)`
   --> $DIR/long-E0529.rs:10:9
    |
 LL |     let [] = x;
-   |         ^^ pattern cannot match with input type `((((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))), (((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32)), ((i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32), (i32, i32, i32, i32))))`
+   |         ^^ pattern cannot match with input type `(..., ..., ..., ...)`
+   |
+   = note: the full name for the type has been written to '$TEST_BUILD_DIR/$FILE.long-type-hash.txt'
+   = note: consider using `--verbose` to print the full type name to the console
 
 error: aborting due to 1 previous error