Add context to "const in pattern" errors

compiler/rustc_mir_build/messages.ftl

@@ -84,12 +84,17 @@ mir_build_call_to_unsafe_fn_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
 
 mir_build_confused = missing patterns are not covered because `{$variable}` is interpreted as a constant pattern, not a new variable
 
-mir_build_const_param_in_pattern = const parameters cannot be referenced in patterns
+mir_build_const_defined_here = constant defined here
 
-mir_build_const_pattern_depends_on_generic_parameter =
-    constant pattern depends on a generic parameter
+mir_build_const_param_in_pattern = constant parameters cannot be referenced in patterns
+    .label = can't be used in patterns
+mir_build_const_param_in_pattern_def = constant defined here
+
+mir_build_const_pattern_depends_on_generic_parameter = constant pattern cannot depend on generic parameters
+    .label = `const` depends on a generic parameter
 
 mir_build_could_not_eval_const_pattern = could not evaluate constant pattern
+    .label = could not evaluate constant
 
 mir_build_deref_raw_pointer_requires_unsafe =
     dereference of raw pointer is unsafe and requires unsafe block
@@ -147,7 +152,8 @@ mir_build_inline_assembly_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
 
 mir_build_interpreted_as_const = introduce a variable instead
 
-mir_build_invalid_pattern = `{$non_sm_ty}` cannot be used in patterns
+mir_build_invalid_pattern = {$prefix} `{$non_sm_ty}` cannot be used in patterns
+    .label = {$prefix} can't be used in patterns
 
 mir_build_irrefutable_let_patterns_if_let = irrefutable `if let` {$count ->
         [one] pattern
@@ -244,10 +250,12 @@ mir_build_mutation_of_layout_constrained_field_requires_unsafe_unsafe_op_in_unsa
     .label = mutation of layout constrained field
 
 mir_build_nan_pattern = cannot use NaN in patterns
+    .label = evaluates to `NaN`, which is not allowed in patterns
     .note = NaNs compare inequal to everything, even themselves, so this pattern would never match
     .help = try using the `is_nan` method instead
 
 mir_build_non_const_path = runtime values cannot be referenced in patterns
+    .label = references a runtime value
 
 mir_build_non_empty_never_pattern =
     mismatched types
@@ -265,13 +273,15 @@ mir_build_non_exhaustive_patterns_type_not_empty = non-exhaustive patterns: type
     .suggestion = ensure that all possible cases are being handled by adding a match arm with a wildcard pattern as shown
     .help = ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
-mir_build_non_partial_eq_match =
-    to use a constant of type `{$non_peq_ty}` in a pattern, the type must implement `PartialEq`
+mir_build_non_partial_eq_match = constant of non-structural type `{$ty}` in a pattern
+    .label = constant of non-structural type
 
 mir_build_pattern_not_covered = refutable pattern in {$origin}
     .pattern_ty = the matched value is of type `{$pattern_ty}`
 
-mir_build_pointer_pattern = function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+mir_build_pointer_pattern = function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon
+    .label = can't be used in patterns
+    .note = see https://github.com/rust-lang/rust/issues/70861 for details
 
 mir_build_privately_uninhabited = pattern `{$witness_1}` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
 
@@ -283,6 +293,8 @@ mir_build_rustc_box_attribute_error = `#[rustc_box]` attribute used incorrectly
     .missing_box = `#[rustc_box]` requires the `owned_box` lang item
 
 mir_build_static_in_pattern = statics cannot be referenced in patterns
+    .label = can't be used in patterns
+mir_build_static_in_pattern_def = `static` defined here
 
 mir_build_suggest_attempted_int_lit = alternatively, you could prepend the pattern with an underscore to define a new named variable; identifiers cannot begin with digits
 
@@ -310,12 +322,12 @@ mir_build_trailing_irrefutable_let_patterns = trailing irrefutable {$count ->
         *[other] them
     } into the body
 
-mir_build_type_not_structural =
-     to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
-
+mir_build_type_not_structural = constant of non-structural type `{$ty}` in a pattern
+    .label = constant of non-structural type
+mir_build_type_not_structural_def = `{$ty}` must be annotated with `#[derive(PartialEq)]` to be usable in patterns
 mir_build_type_not_structural_more_info = see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
-
-mir_build_type_not_structural_tip = the traits must be derived, manual `impl`s are not sufficient
+mir_build_type_not_structural_tip =
+    the `PartialEq` trait must be derived, manual `impl`s are not sufficient; see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
 
 mir_build_unconditional_recursion = function cannot return without recursing
     .label = cannot return without recursing
@@ -334,6 +346,7 @@ mir_build_union_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
     .label = access to union field
 
 mir_build_union_pattern = cannot use unions in constant patterns
+    .label = can't use a `union` here
 
 mir_build_unreachable_making_this_unreachable = collectively making this unreachable
 

compiler/rustc_mir_build/src/errors.rs

@@ -631,20 +631,27 @@ pub(crate) struct NonExhaustiveMatchAllArmsGuarded;
 #[diag(mir_build_static_in_pattern, code = E0158)]
 pub(crate) struct StaticInPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
+    #[label(mir_build_static_in_pattern_def)]
+    pub(crate) static_span: Span,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_const_param_in_pattern, code = E0158)]
 pub(crate) struct ConstParamInPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
+    #[label(mir_build_const_param_in_pattern_def)]
+    pub(crate) const_span: Span,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_non_const_path, code = E0080)]
 pub(crate) struct NonConstPath {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }
 
@@ -695,13 +702,15 @@ pub(crate) struct WantedConstant {
 #[diag(mir_build_const_pattern_depends_on_generic_parameter, code = E0158)]
 pub(crate) struct ConstPatternDependsOnGenericParameter {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_could_not_eval_const_pattern)]
 pub(crate) struct CouldNotEvalConstPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }
 
@@ -867,33 +876,43 @@ pub(crate) enum Conflict {
 #[diag(mir_build_union_pattern)]
 pub(crate) struct UnionPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_type_not_structural)]
-#[note(mir_build_type_not_structural_tip)]
-#[note(mir_build_type_not_structural_more_info)]
 pub(crate) struct TypeNotStructural<'tcx> {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
-    pub(crate) non_sm_ty: Ty<'tcx>,
+    #[label(mir_build_type_not_structural_def)]
+    pub(crate) ty_def_span: Span,
+    pub(crate) ty: Ty<'tcx>,
+    #[note(mir_build_type_not_structural_tip)]
+    pub(crate) manual_partialeq_impl_span: Option<Span>,
+    #[note(mir_build_type_not_structural_more_info)]
+    pub(crate) manual_partialeq_impl_note: bool,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_non_partial_eq_match)]
+#[note(mir_build_type_not_structural_more_info)]
 pub(crate) struct TypeNotPartialEq<'tcx> {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
-    pub(crate) non_peq_ty: Ty<'tcx>,
+    pub(crate) ty: Ty<'tcx>,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_invalid_pattern)]
 pub(crate) struct InvalidPattern<'tcx> {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
     pub(crate) non_sm_ty: Ty<'tcx>,
+    pub(crate) prefix: String,
 }
 
 #[derive(Diagnostic)]
@@ -910,13 +929,16 @@ pub(crate) struct UnsizedPattern<'tcx> {
 #[help]
 pub(crate) struct NaNPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }
 
 #[derive(Diagnostic)]
 #[diag(mir_build_pointer_pattern)]
+#[note]
 pub(crate) struct PointerPattern {
     #[primary_span]
+    #[label]
     pub(crate) span: Span,
 }