1 files changed, 108 insertions, 0 deletions
diff --git a/compiler/rustc_pattern_analysis/src/lints.rs b/compiler/rustc_pattern_analysis/src/lints.rs
new file mode 100644
index 00000000000..892aacd7ac5
--- /dev/null
+++ b/compiler/rustc_pattern_analysis/src/lints.rs
@@ -0,0 +1,108 @@
+use crate::constructor::Constructor;
+use crate::errors::{NonExhaustiveOmittedPattern, NonExhaustiveOmittedPatternLintOnArm, Uncovered};
+use crate::pat_column::PatternColumn;
+use crate::rustc::{RevealedTy, RustcPatCtxt, WitnessPat};
+use crate::MatchArm;
+use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
+use rustc_span::ErrorGuaranteed;
+use tracing::instrument;
+
+/// Traverse the patterns to collect any variants of a non_exhaustive enum that fail to be mentioned
+/// in a given column.
+#[instrument(level = "debug", skip(cx), ret)]
+fn collect_nonexhaustive_missing_variants<'p, 'tcx>(
+    cx: &RustcPatCtxt<'p, 'tcx>,
+    column: &PatternColumn<'p, RustcPatCtxt<'p, 'tcx>>,
+) -> Result<Vec<WitnessPat<'p, 'tcx>>, ErrorGuaranteed> {
+    let Some(&ty) = column.head_ty() else {
+        return Ok(Vec::new());
+    };
+
+    let set = column.analyze_ctors(cx, &ty)?;
+    if set.present.is_empty() {
+        // We can't consistently handle the case where no constructors are present (since this would
+        // require digging deep through any type in case there's a non_exhaustive enum somewhere),
+        // so for consistency we refuse to handle the top-level case, where we could handle it.
+        return Ok(Vec::new());
+    }
+
+    let mut witnesses = Vec::new();
+    if cx.is_foreign_non_exhaustive_enum(ty) {
+        witnesses.extend(
+            set.missing
+                .into_iter()
+                // This will list missing visible variants.
+                .filter(|c| !matches!(c, Constructor::Hidden | Constructor::NonExhaustive))
+                .map(|missing_ctor| WitnessPat::wild_from_ctor(cx, missing_ctor, ty)),
+        )
+    }
+
+    // Recurse into the fields.
+    for ctor in set.present {
+        let specialized_columns = column.specialize(cx, &ty, &ctor);
+        let wild_pat = WitnessPat::wild_from_ctor(cx, ctor, ty);
+        for (i, col_i) in specialized_columns.iter().enumerate() {
+            // Compute witnesses for each column.
+            let wits_for_col_i = collect_nonexhaustive_missing_variants(cx, col_i)?;
+            // For each witness, we build a new pattern in the shape of `ctor(_, _, wit, _, _)`,
+            // adding enough wildcards to match `arity`.
+            for wit in wits_for_col_i {
+                let mut pat = wild_pat.clone();
+                pat.fields[i] = wit;
+                witnesses.push(pat);
+            }
+        }
+    }
+    Ok(witnesses)
+}
+
+pub(crate) fn lint_nonexhaustive_missing_variants<'p, 'tcx>(
+    rcx: &RustcPatCtxt<'p, 'tcx>,
+    arms: &[MatchArm<'p, RustcPatCtxt<'p, 'tcx>>],
+    pat_column: &PatternColumn<'p, RustcPatCtxt<'p, 'tcx>>,
+    scrut_ty: RevealedTy<'tcx>,
+) -> Result<(), ErrorGuaranteed> {
+    if !matches!(
+        rcx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, rcx.match_lint_level).0,
+        rustc_session::lint::Level::Allow
+    ) {
+        let witnesses = collect_nonexhaustive_missing_variants(rcx, pat_column)?;
+        if !witnesses.is_empty() {
+            // Report that a match of a `non_exhaustive` enum marked with `non_exhaustive_omitted_patterns`
+            // is not exhaustive enough.
+            //
+            // NB: The partner lint for structs lives in `compiler/rustc_hir_analysis/src/check/pat.rs`.
+            rcx.tcx.emit_node_span_lint(
+                NON_EXHAUSTIVE_OMITTED_PATTERNS,
+                rcx.match_lint_level,
+                rcx.scrut_span,
+                NonExhaustiveOmittedPattern {
+                    scrut_ty: scrut_ty.inner(),
+                    uncovered: Uncovered::new(rcx.scrut_span, rcx, witnesses),
+                },
+            );
+        }
+    } else {
+        // We used to allow putting the `#[allow(non_exhaustive_omitted_patterns)]` on a match
+        // arm. This no longer makes sense so we warn users, to avoid silently breaking their
+        // usage of the lint.
+        for arm in arms {
+            let (lint_level, lint_level_source) =
+                rcx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, arm.arm_data);
+            if !matches!(lint_level, rustc_session::lint::Level::Allow) {
+                let decorator = NonExhaustiveOmittedPatternLintOnArm {
+                    lint_span: lint_level_source.span(),
+                    suggest_lint_on_match: rcx.whole_match_span.map(|span| span.shrink_to_lo()),
+                    lint_level: lint_level.as_str(),
+                    lint_name: "non_exhaustive_omitted_patterns",
+                };
+
+                use rustc_errors::LintDiagnostic;
+                let mut err = rcx.tcx.dcx().struct_span_warn(arm.pat.data().span, "");
+                decorator.decorate_lint(&mut err);
+                err.emit();
+            }
+        }
+    }
+    Ok(())
+}