Rewrite non_exhaustive_omitted_patterns as a separate pass

compiler/rustc_lint_defs/src/builtin.rs

@@ -3798,8 +3798,10 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `non_exhaustive_omitted_patterns` lint detects when a wildcard (`_` or `..`) in a
-    /// pattern for a `#[non_exhaustive]` struct or enum is reachable.
+    /// The `non_exhaustive_omitted_patterns` lint detects when some variants or fields of a
+    /// `#[non_exhaustive]` struct or enum are not mentioned explicitly in a pattern. This allows
+    /// downstream crates to be warned when new variants or fields are added to the upstream struct
+    /// or enum.
     ///
     /// ### Example
     ///
@@ -3814,9 +3816,9 @@ declare_lint! {
     /// // in crate B
     /// #![feature(non_exhaustive_omitted_patterns_lint)]
     ///
+    /// #[warn(non_exhaustive_omitted_patterns)]
     /// match Bar::A {
     ///     Bar::A => {},
-    ///     #[warn(non_exhaustive_omitted_patterns)]
     ///     _ => {},
     /// }
     /// ```
@@ -3827,8 +3829,8 @@ declare_lint! {
     /// warning: reachable patterns not covered of non exhaustive enum
     ///    --> $DIR/reachable-patterns.rs:70:9
     ///    |
-    /// LL |         _ => {}
-    ///    |         ^ pattern `B` not covered
+    /// LL |         match Bar::A {
+    ///    |               ^ pattern `Bar::B` not covered
     ///    |
     ///  note: the lint level is defined here
     ///   --> $DIR/reachable-patterns.rs:69:16
@@ -3841,12 +3843,11 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// Structs and enums tagged with `#[non_exhaustive]` force the user to add a
-    /// (potentially redundant) wildcard when pattern-matching, to allow for future
-    /// addition of fields or variants. The `non_exhaustive_omitted_patterns` lint
-    /// detects when such a wildcard happens to actually catch some fields/variants.
-    /// In other words, when the match without the wildcard would not be exhaustive.
-    /// This lets the user be informed if new fields/variants were added.
+    /// Structs and enums tagged with `#[non_exhaustive]` force the user to add a (potentially
+    /// redundant) wildcard when pattern-matching, to allow for future addition of fields or
+    /// variants. The `non_exhaustive_omitted_patterns` lint detects when such a wildcard happens to
+    /// actually catch some fields/variants. This lets the user be informed if new fields/variants
+    /// were added.
     pub NON_EXHAUSTIVE_OMITTED_PATTERNS,
     Allow,
     "detect when patterns of types marked `non_exhaustive` are missed",

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

@@ -250,7 +250,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
 
         let scrut = &self.thir[scrut];
         let scrut_ty = scrut.ty;
-        let report = compute_match_usefulness(&cx, &tarms, self.lint_level, scrut_ty);
+        let report = compute_match_usefulness(&cx, &tarms, self.lint_level, scrut_ty, scrut.span);
 
         match source {
             // Don't report arm reachability of desugared `match $iter.into_iter() { iter => .. }`
@@ -415,7 +415,8 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         let pattern = self.lower_pattern(&mut cx, pat);
         let pattern_ty = pattern.ty();
         let arm = MatchArm { pat: pattern, hir_id: self.lint_level, has_guard: false };
-        let report = compute_match_usefulness(&cx, &[arm], self.lint_level, pattern_ty);
+        let report =
+            compute_match_usefulness(&cx, &[arm], self.lint_level, pattern_ty, pattern.span());
 
         // Note: we ignore whether the pattern is unreachable (i.e. whether the type is empty). We
         // only care about exhaustiveness here.
@@ -583,7 +584,7 @@ fn is_let_irrefutable<'p, 'tcx>(
     pat: &'p DeconstructedPat<'p, 'tcx>,
 ) -> bool {
     let arms = [MatchArm { pat, hir_id: pat_id, has_guard: false }];
-    let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty());
+    let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty(), pat.span());
 
     // Report if the pattern is unreachable, which can only occur when the type is uninhabited.
     // This also reports unreachable sub-patterns though, so we can't just replace it with an

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

@@ -643,9 +643,8 @@ pub(super) enum Constructor<'tcx> {
     /// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
     NonExhaustive,
     /// Stands for constructors that are not seen in the matrix, as explained in the documentation
-    /// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
-    /// lint.
-    Missing { nonexhaustive_enum_missing_real_variants: bool },
+    /// for [`SplitWildcard`].
+    Missing,
     /// Wildcard pattern.
     Wildcard,
     /// Or-pattern.
@@ -1053,6 +1052,16 @@ impl<'tcx> SplitWildcard<'tcx> {
         self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
     }
 
+    /// Iterate over the constructors for this type that are present in the matrix. This has the
+    /// effect of deduplicating present constructors.
+    /// WARNING: this omits special constructors like `Wildcard` and `Opaque`.
+    pub(super) fn iter_present<'a, 'p>(
+        &'a self,
+        pcx: &'a PatCtxt<'a, 'p, 'tcx>,
+    ) -> impl Iterator<Item = &'a Constructor<'tcx>> + Captures<'p> {
+        self.all_ctors.iter().filter(move |ctor| ctor.is_covered_by_any(pcx, &self.matrix_ctors))
+    }
+
     /// Return the set of constructors resulting from splitting the wildcard. As explained at the
     /// top of the file, if any constructors are missing we can ignore the present ones.
     fn into_ctors(self, pcx: &PatCtxt<'_, '_, 'tcx>) -> SmallVec<[Constructor<'tcx>; 1]> {
@@ -1086,15 +1095,7 @@ impl<'tcx> SplitWildcard<'tcx> {
             // sometimes prefer reporting the list of constructors instead of just `_`.
             let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
             let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
-                if pcx.is_non_exhaustive {
-                    Missing {
-                        nonexhaustive_enum_missing_real_variants: self
-                            .iter_missing(pcx)
-                            .any(|c| !(c.is_non_exhaustive() || c.is_unstable_variant(pcx))),
-                    }
-                } else {
-                    Missing { nonexhaustive_enum_missing_real_variants: false }
-                }
+                Missing
             } else {
                 Wildcard
             };
@@ -1240,9 +1241,10 @@ impl<'p, 'tcx> Fields<'p, 'tcx> {
 
 /// Values and patterns can be represented as a constructor applied to some fields. This represents
 /// a pattern in this form.
-/// This also keeps track of whether the pattern has been found reachable during analysis. For this
-/// reason we should be careful not to clone patterns for which we care about that. Use
-/// `clone_and_forget_reachability` if you're sure.
+/// This also uses interior mutability to keep track of whether the pattern has been found reachable
+/// during analysis. For this reason we should be careful not to clone patterns for which we care
+/// about that.
+#[derive(Clone)]
 pub(crate) struct DeconstructedPat<'p, 'tcx> {
     ctor: Constructor<'tcx>,
     fields: Fields<'p, 'tcx>,
@@ -1273,12 +1275,6 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
         DeconstructedPat::new(ctor, fields, pcx.ty, pcx.span)
     }
 
-    /// Clone this value. This method emphasizes that cloning loses reachability information and
-    /// should be done carefully.
-    pub(super) fn clone_and_forget_reachability(&self) -> Self {
-        DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty, self.span)
-    }
-
     pub(crate) fn from_pat(cx: &MatchCheckCtxt<'p, 'tcx>, pat: &Pat<'tcx>) -> Self {
         let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
         let ctor;
@@ -1522,6 +1518,13 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
     pub(super) fn is_or_pat(&self) -> bool {
         matches!(self.ctor, Or)
     }
+    pub(super) fn flatten_or_pat(&'p self) -> SmallVec<[&'p Self; 1]> {
+        if self.is_or_pat() {
+            self.iter_fields().flat_map(|p| p.flatten_or_pat()).collect()
+        } else {
+            smallvec![self]
+        }
+    }
 
     pub(super) fn ctor(&self) -> &Constructor<'tcx> {
         &self.ctor
@@ -1596,7 +1599,6 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
         self.collect_unreachable_spans(&mut spans);
         spans
     }
-
     fn collect_unreachable_spans(&self, spans: &mut Vec<Span>) {
         // We don't look at subpatterns if we already reported the whole pattern as unreachable.
         if !self.is_reachable() {