Suggest to set lint level on whole match

compiler/rustc_mir_build/messages.ftl

@@ -221,8 +221,10 @@ mir_build_non_exhaustive_omitted_pattern = some variants are not matched explici
  .help = ensure that all variants are matched explicitly by adding the suggested match arms
  .note = the matched value is of type `{$scrut_ty}` and the `non_exhaustive_omitted_patterns` attribute was found
 
-mir_build_non_exhaustive_omitted_pattern_lint_on_arm = the `non_exhaustive_omitted_pattern` lint level must be set on the whole match
- .help = it used to make sense to set the lint level on an individual match arm, but that is no longer the case
+mir_build_non_exhaustive_omitted_pattern_lint_on_arm = the lint level must be set on the whole match
+ .help = it no longer has any effect to set the lint level on an individual match arm
+ .label = remove this attribute
+ .suggestion = set the lint level on the whole match
 
 mir_build_non_exhaustive_patterns_type_not_empty = non-exhaustive patterns: type `{$ty}` is non-empty
  .def_note = `{$peeled_ty}` defined here

compiler/rustc_mir_build/src/errors.rs

@@ -792,7 +792,14 @@ pub(crate) struct NonExhaustiveOmittedPattern<'tcx> {
 #[derive(LintDiagnostic)]
 #[diag(mir_build_non_exhaustive_omitted_pattern_lint_on_arm)]
 #[help]
-pub(crate) struct NonExhaustiveOmittedPatternLintOnArm;
+pub(crate) struct NonExhaustiveOmittedPatternLintOnArm {
+ #[label]
+ pub lint_span: Span,
+ #[suggestion(code = "#[{lint_level}({lint_name})]\n", applicability = "maybe-incorrect")]
+ pub suggest_lint_on_match: Option<Span>,
+ pub lint_level: &'static str,
+ pub lint_name: &'static str,
+}
 
 #[derive(Subdiagnostic)]
 #[label(mir_build_uncovered)]

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

@@ -218,12 +218,18 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
  cx.pattern_arena.alloc(DeconstructedPat::from_pat(cx, &pattern))
  }
 
- fn new_cx(&self, hir_id: HirId, refutable: bool) -> MatchCheckCtxt<'p, 'tcx> {
+ fn new_cx(
+ &self,
+ hir_id: HirId,
+ refutable: bool,
+ match_span: Option<Span>,
+ ) -> MatchCheckCtxt<'p, 'tcx> {
  MatchCheckCtxt {
  tcx: self.tcx,
  param_env: self.param_env,
  module: self.tcx.parent_module(hir_id).to_def_id(),
  pattern_arena: &self.pattern_arena,
+ match_span,
  refutable,
  }
  }
@@ -238,7 +244,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
  return;
  }
  self.check_patterns(pat, Refutable);
- let mut cx = self.new_cx(self.lint_level, true);
+ let mut cx = self.new_cx(self.lint_level, true, None);
  let tpat = self.lower_pattern(&mut cx, pat);
  self.check_let_reachability(&mut cx, self.lint_level, source, tpat, span);
  }
@@ -250,7 +256,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
  source: hir::MatchSource,
  expr_span: Span,
  ) {
- let mut cx = self.new_cx(self.lint_level, true);
+ let mut cx = self.new_cx(self.lint_level, true, Some(expr_span));
 
  for &arm in arms {
  // Check the arm for some things unrelated to exhaustiveness.
@@ -363,7 +369,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
  error = Err(err);
  return None;
  }
- let mut ncx = self.new_cx(local_lint_level, true);
+ let mut ncx = self.new_cx(local_lint_level, true, None);
  let tpat = self.lower_pattern(&mut ncx, pat);
  let refutable = !is_let_irrefutable(&mut ncx, local_lint_level, tpat);
  Some((expr.span, refutable))
@@ -468,7 +474,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
  return;
  }
 
- let mut cx = self.new_cx(self.lint_level, false);
+ let mut cx = self.new_cx(self.lint_level, false, None);
 
  let pattern = self.lower_pattern(&mut cx, pat);
  let pattern_ty = pattern.ty();

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

@@ -340,6 +340,8 @@ pub(crate) struct MatchCheckCtxt<'p, 'tcx> {
  pub(crate) module: DefId,
  pub(crate) param_env: ty::ParamEnv<'tcx>,
  pub(crate) pattern_arena: &'p TypedArena<DeconstructedPat<'p, 'tcx>>,
+ /// The span of the whole match, if applicable.
+ pub(crate) match_span: Option<Span>,
  /// Only produce `NON_EXHAUSTIVE_OMITTED_PATTERNS` lint on refutable patterns.
  pub(crate) refutable: bool,
 }
@@ -1179,16 +1181,21 @@ pub(crate) fn compute_match_usefulness<'p, 'tcx>(
  // arm. This no longer makes sense so we warn users, to avoid silently breaking their
  // usage of the lint.
  for arm in arms {
- if !matches!(
- cx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, arm.hir_id).0,
- rustc_session::lint::Level::Allow
- ) {
- cx.tcx.emit_spanned_lint(
- NON_EXHAUSTIVE_OMITTED_PATTERNS,
- arm.hir_id,
- arm.pat.span(),
- NonExhaustiveOmittedPatternLintOnArm,
- );
+ let (lint_level, lint_level_source) =
+ cx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, arm.hir_id);
+ if !matches!(lint_level, rustc_session::lint::Level::Allow) {
+ let decorator = NonExhaustiveOmittedPatternLintOnArm {
+ lint_span: lint_level_source.span(),
+ suggest_lint_on_match: cx.match_span.map(|span| span.shrink_to_lo()),
+ lint_level: lint_level.as_str(),
+ lint_name: "non_exhaustive_omitted_patterns",
+ };
+
+ use rustc_errors::DecorateLint;
+ let mut err = cx.tcx.sess.struct_span_warn(arm.pat.span(), "");
+ err.set_primary_message(decorator.msg());
+ decorator.decorate_lint(&mut err);
+ err.emit();
  }
  }
  }

tests/ui/rfcs/rfc-2008-non-exhaustive/omitted-patterns-dont-lint-on-arm.lint.stderr

@@ -26,44 +26,50 @@ note: the lint level is defined here
 LL | #[cfg_attr(lint, deny(non_exhaustive_omitted_patterns))]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: the `non_exhaustive_omitted_pattern` lint level must be set on the whole match
+warning: the lint level must be set on the whole match
  --> $DIR/omitted-patterns-dont-lint-on-arm.rs:34:9
  |
+LL | #[deny(non_exhaustive_omitted_patterns)]
+ | ------------------------------- remove this attribute
 LL | _ => {}
  | ^
  |
- = help: it used to make sense to set the lint level on an individual match arm, but that is no longer the case
-note: the lint level is defined here
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:33:16
+ = help: it no longer has any effect to set the lint level on an individual match arm
+help: set the lint level on the whole match
+ |
+LL + #[deny(non_exhaustive_omitted_patterns)]
+LL | match val {
  |
-LL | #[deny(non_exhaustive_omitted_patterns)]
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: the `non_exhaustive_omitted_pattern` lint level must be set on the whole match
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:41:9
+warning: the lint level must be set on the whole match
+ --> $DIR/omitted-patterns-dont-lint-on-arm.rs:42:9
  |
+LL | #[cfg_attr(lint, deny(non_exhaustive_omitted_patterns))]
+ | ------------------------------- remove this attribute
 LL | _ => {}
  | ^
  |
- = help: it used to make sense to set the lint level on an individual match arm, but that is no longer the case
-note: the lint level is defined here
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:40:31
+ = help: it no longer has any effect to set the lint level on an individual match arm
+help: set the lint level on the whole match
+ |
+LL + #[deny(non_exhaustive_omitted_patterns)]
+LL | match val {
  |
-LL | #[cfg_attr(lint, deny(non_exhaustive_omitted_patterns))]
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: the `non_exhaustive_omitted_pattern` lint level must be set on the whole match
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:48:9
+warning: the lint level must be set on the whole match
+ --> $DIR/omitted-patterns-dont-lint-on-arm.rs:50:9
  |
+LL | #[cfg_attr(lint, warn(non_exhaustive_omitted_patterns))]
+ | ------------------------------- remove this attribute
 LL | _ => {}
  | ^
  |
- = help: it used to make sense to set the lint level on an individual match arm, but that is no longer the case
-note: the lint level is defined here
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:47:31
+ = help: it no longer has any effect to set the lint level on an individual match arm
+help: set the lint level on the whole match
+ |
+LL + #[warn(non_exhaustive_omitted_patterns)]
+LL | match val {
  |
-LL | #[cfg_attr(lint, warn(non_exhaustive_omitted_patterns))]
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors; 1 warning emitted
+error: aborting due to 2 previous errors; 3 warnings emitted
 

tests/ui/rfcs/rfc-2008-non-exhaustive/omitted-patterns-dont-lint-on-arm.normal.stderr

@@ -12,18 +12,20 @@ note: the lint level is defined here
 LL | #[deny(non_exhaustive_omitted_patterns)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: the `non_exhaustive_omitted_pattern` lint level must be set on the whole match
+warning: the lint level must be set on the whole match
  --> $DIR/omitted-patterns-dont-lint-on-arm.rs:34:9
  |
+LL | #[deny(non_exhaustive_omitted_patterns)]
+ | ------------------------------- remove this attribute
 LL | _ => {}
  | ^
  |
- = help: it used to make sense to set the lint level on an individual match arm, but that is no longer the case
-note: the lint level is defined here
- --> $DIR/omitted-patterns-dont-lint-on-arm.rs:33:16
+ = help: it no longer has any effect to set the lint level on an individual match arm
+help: set the lint level on the whole match
+ |
+LL + #[deny(non_exhaustive_omitted_patterns)]
+LL | match val {
  |
-LL | #[deny(non_exhaustive_omitted_patterns)]
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error; 1 warning emitted
 

tests/ui/rfcs/rfc-2008-non-exhaustive/omitted-patterns-dont-lint-on-arm.rs

@@ -31,20 +31,23 @@ fn main() {
  NonExhaustiveEnum::Unit => {}
  NonExhaustiveEnum::Tuple(_) => {}
  #[deny(non_exhaustive_omitted_patterns)]
- _ => {} //~ ERROR lint level must be set on the whole match
+ _ => {}
  }
+ //~^^ WARN lint level must be set on the whole match
 
  match val {
  NonExhaustiveEnum::Unit => {}
  NonExhaustiveEnum::Tuple(_) => {}
  #[cfg_attr(lint, deny(non_exhaustive_omitted_patterns))]
- _ => {} //[lint]~ ERROR lint level must be set on the whole match
+ _ => {}
  }
+ //[lint]~^^ WARN lint level must be set on the whole match
 
  match val {
  NonExhaustiveEnum::Unit => {}
  NonExhaustiveEnum::Tuple(_) => {}
  #[cfg_attr(lint, warn(non_exhaustive_omitted_patterns))]
- _ => {} //[lint]~ WARN lint level must be set on the whole match
+ _ => {}
  }
+ //[lint]~^^ WARN lint level must be set on the whole match
 }