feat: `min-exhaustive-patterns

Author: ShoyuVanilla

crates/hir-ty/src/diagnostics/expr.rs

@@ -4,28 +4,33 @@
 
 use std::fmt;
 
+use chalk_solve::rust_ir::AdtKind;
 use either::Either;
-use hir_def::lang_item::LangItem;
-use hir_def::{resolver::HasResolver, AdtId, AssocItemId, DefWithBodyId, HasModule};
-use hir_def::{ItemContainerId, Lookup};
+use hir_def::{
+    lang_item::LangItem,
+    resolver::{HasResolver, ValueNs},
+    AdtId, AssocItemId, DefWithBodyId, HasModule, ItemContainerId, Lookup,
+};
 use intern::sym;
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
 use rustc_pattern_analysis::constructor::Constructor;
-use syntax::{ast, AstNode};
+use syntax::{
+    ast::{self, UnaryOp},
+    AstNode,
+};
 use tracing::debug;
 use triomphe::Arc;
 use typed_arena::Arena;
 
-use crate::Interner;
 use crate::{
     db::HirDatabase,
     diagnostics::match_check::{
         self,
         pat_analysis::{self, DeconstructedPat, MatchCheckCtx, WitnessPat},
     },
     display::HirDisplay,
-    InferenceResult, Ty, TyExt,
+    Adjust, InferenceResult, Interner, Ty, TyExt, TyKind,
 };
 
 pub(crate) use hir_def::{
@@ -236,7 +241,12 @@ impl ExprValidator {
             return;
         }
 
-        let report = match cx.compute_match_usefulness(m_arms.as_slice(), scrut_ty.clone()) {
+        let known_valid_scrutinee = Some(self.is_known_valid_scrutinee(scrutinee_expr, db));
+        let report = match cx.compute_match_usefulness(
+            m_arms.as_slice(),
+            scrut_ty.clone(),
+            known_valid_scrutinee,
+        ) {
             Ok(report) => report,
             Err(()) => return,
         };
@@ -253,6 +263,45 @@ impl ExprValidator {
         }
     }
 
+    // [rustc's `is_known_valid_scrutinee`](https://github.com/rust-lang/rust/blob/c9bd03cb724e13cca96ad320733046cbdb16fbbe/compiler/rustc_mir_build/src/thir/pattern/check_match.rs#L288)
+    //
+    // While the above function in rustc uses thir exprs, r-a doesn't have them.
+    // So, the logic here is getting same result as "hir lowering + match with lowered thir"
+    // with "hir only"
+    fn is_known_valid_scrutinee(&self, scrutinee_expr: ExprId, db: &dyn HirDatabase) -> bool {
+        if self
+            .infer
+            .expr_adjustments
+            .get(&scrutinee_expr)
+            .is_some_and(|adjusts| adjusts.iter().any(|a| matches!(a.kind, Adjust::Deref(..))))
+        {
+            return false;
+        }
+
+        match &self.body[scrutinee_expr] {
+            Expr::UnaryOp { op: UnaryOp::Deref, .. } => false,
+            Expr::Path(path) => {
+                let value_or_partial = self
+                    .owner
+                    .resolver(db.upcast())
+                    .resolve_path_in_value_ns_fully(db.upcast(), path);
+                value_or_partial.map_or(true, |v| !matches!(v, ValueNs::StaticId(_)))
+            }
+            Expr::Field { expr, .. } => match self.infer.type_of_expr[*expr].kind(Interner) {
+                TyKind::Adt(adt, ..)
+                    if db.adt_datum(self.owner.krate(db.upcast()), *adt).kind == AdtKind::Union =>
+                {
+                    false
+                }
+                _ => self.is_known_valid_scrutinee(*expr, db),
+            },
+            Expr::Index { base, .. } => self.is_known_valid_scrutinee(*base, db),
+            Expr::Cast { expr, .. } => self.is_known_valid_scrutinee(*expr, db),
+            Expr::Missing => false,
+            _ => true,
+        }
+    }
+
     fn validate_block(&mut self, db: &dyn HirDatabase, expr: &Expr) {
         let Expr::Block { statements, .. } = expr else { return };
         let pattern_arena = Arena::new();
@@ -280,7 +329,7 @@ impl ExprValidator {
                 has_guard: false,
                 arm_data: (),
             };
-            let report = match cx.compute_match_usefulness(&[match_arm], ty.clone()) {
+            let report = match cx.compute_match_usefulness(&[match_arm], ty.clone(), None) {
                 Ok(v) => v,
                 Err(e) => {
                     debug!(?e, "match usefulness error");

crates/hir-ty/src/diagnostics/match_check/pat_analysis.rs

@@ -69,22 +69,20 @@ pub(crate) struct MatchCheckCtx<'db> {
     body: DefWithBodyId,
     pub(crate) db: &'db dyn HirDatabase,
     exhaustive_patterns: bool,
-    min_exhaustive_patterns: bool,
 }
 
 impl<'db> MatchCheckCtx<'db> {
     pub(crate) fn new(module: ModuleId, body: DefWithBodyId, db: &'db dyn HirDatabase) -> Self {
         let def_map = db.crate_def_map(module.krate());
         let exhaustive_patterns = def_map.is_unstable_feature_enabled(&sym::exhaustive_patterns);
-        let min_exhaustive_patterns =
-            def_map.is_unstable_feature_enabled(&sym::min_exhaustive_patterns);
-        Self { module, body, db, exhaustive_patterns, min_exhaustive_patterns }
+        Self { module, body, db, exhaustive_patterns }
     }
 
     pub(crate) fn compute_match_usefulness(
         &self,
         arms: &[MatchArm<'db>],
         scrut_ty: Ty,
+        known_valid_scrutinee: Option<bool>,
     ) -> Result<UsefulnessReport<'db, Self>, ()> {
         if scrut_ty.contains_unknown() {
             return Err(());
@@ -95,8 +93,7 @@ impl<'db> MatchCheckCtx<'db> {
             }
         }
 
-        // FIXME: Determine place validity correctly. For now, err on the safe side.
-        let place_validity = PlaceValidity::MaybeInvalid;
+        let place_validity = PlaceValidity::from_bool(known_valid_scrutinee.unwrap_or(true));
         // Measured to take ~100ms on modern hardware.
         let complexity_limit = Some(500000);
         compute_match_usefulness(self, arms, scrut_ty, place_validity, complexity_limit)
@@ -328,7 +325,7 @@ impl<'db> PatCx for MatchCheckCtx<'db> {
         self.exhaustive_patterns
     }
     fn is_min_exhaustive_patterns_feature_on(&self) -> bool {
-        self.min_exhaustive_patterns
+        true
     }
 
     fn ctor_arity(

crates/ide-diagnostics/src/handlers/missing_match_arms.rs

@@ -1032,6 +1032,44 @@ fn f() {
         check_diagnostics_no_bails(&code);
     }
 
+    #[test]
+    fn min_exhaustive() {
+        check_diagnostics(
+            r#"
+//- minicore: result
+fn test(x: Result<i32, !>) {
+    match x {
+        Ok(_y) => {}
+    }
+}
+"#,
+        );
+        check_diagnostics(
+            r#"
+//- minicore: result
+fn test(ptr: *const Result<i32, !>) {
+    unsafe {
+        match *ptr {
+            //^^^^ error: missing match arm: `Err(!)` not covered
+            Ok(_x) => {}
+        }
+    }
+}
+"#,
+        );
+        check_diagnostics(
+            r#"
+//- minicore: result
+fn test(x: Result<i32, &'static !>) {
+    match x {
+        //^ error: missing match arm: `Err(_)` not covered
+        Ok(_y) => {}
+    }
+}
+"#,
+        );
+    }
+
     mod rust_unstable {
         use super::*;
 

crates/ide-diagnostics/src/handlers/non_exhaustive_let.rs

@@ -41,6 +41,27 @@ fn main() {
 fn main() {
     let Some(_) | None = Some(5);
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn min_exhaustive() {
+        check_diagnostics(
+            r#"
+//- minicore: result
+fn test(x: Result<i32, !>) {
+    let Ok(_y) = x;
+}
+"#,
+        );
+        check_diagnostics(
+            r#"
+//- minicore: result
+fn test(x: Result<i32, &'static !>) {
+    let Ok(_y) = x;
+      //^^^^^^ error: non-exhaustive pattern: `Err(_)` not covered
+}
 "#,
         );
     }