Auto merge of #117673 - matthewjasper:thir-unsafeck-stabilization, r=cjgillot

Stabilize THIR unsafeck

- Removes `-Zthir-unsafeck`, stabilizing the behaviour of `-Zthir-unsafeck=on`.
- Removes MIR unsafeck.
- Union patterns are now unsafe unless the field is matched to a wildcard pattern.

Opening for a crater run in case we need a compatibility lint.

9 files changed, 33 insertions, 26 deletions

diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 559874641c3..ce76c2cba93 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -735,9 +735,9 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> {
 
     sess.time("MIR_borrow_checking", || {
         tcx.hir().par_body_owners(|def_id| {
-            // Run THIR unsafety check because it's responsible for stealing
-            // and deallocating THIR when enabled.
-            tcx.ensure().thir_check_unsafety(def_id);
+            // Run unsafety check because it's responsible for stealing and
+            // deallocating THIR.
+            tcx.ensure().check_unsafety(def_id);
             tcx.ensure().mir_borrowck(def_id)
         });
     });
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index c4a1f3a0e51..75410db1e36 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -822,7 +822,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(stack_protector, StackProtector::All);
     tracked!(teach, true);
     tracked!(thinlto, Some(true));
-    tracked!(thir_unsafeck, true);
+    tracked!(thir_unsafeck, false);
     tracked!(tiny_const_eval_limit, true);
     tracked!(tls_model, Some(TlsModel::GeneralDynamic));
     tracked!(translate_remapped_path_to_local_path, false);
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 5c425fef27e..0a1a72b442a 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -720,7 +720,7 @@ pub struct SourceInfo {
     pub span: Span,
 
     /// The source scope, keeping track of which bindings can be
-    /// seen by debuginfo, active lint levels, `unsafe {...}`, etc.
+    /// seen by debuginfo, active lint levels, etc.
     pub scope: SourceScope,
 }
 
@@ -942,7 +942,7 @@ pub struct LocalDecl<'tcx> {
 
 /// Extra information about a some locals that's used for diagnostics and for
 /// classifying variables into local variables, statics, etc, which is needed e.g.
-/// for unsafety checking.
+/// for borrow checking.
 ///
 /// Not used for non-StaticRef temporaries, the return place, or anonymous
 /// function parameters.
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 2810182c0a0..bf5e59ba78d 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -869,15 +869,14 @@ rustc_queries! {
         desc { |tcx| "collecting all inherent impls for `{:?}`", key }
     }
 
-    /// The result of unsafety-checking this `LocalDefId`.
-    query unsafety_check_result(key: LocalDefId) -> &'tcx mir::UnsafetyCheckResult {
+    /// The result of unsafety-checking this `LocalDefId` with the old checker.
+    query mir_unsafety_check_result(key: LocalDefId) -> &'tcx mir::UnsafetyCheckResult {
         desc { |tcx| "unsafety-checking `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { true }
     }
 
-    /// Unsafety-check this `LocalDefId` with THIR unsafeck. This should be
-    /// used with `-Zthir-unsafeck`.
-    query thir_check_unsafety(key: LocalDefId) {
+    /// Unsafety-check this `LocalDefId`.
+    query check_unsafety(key: LocalDefId) {
         desc { |tcx| "unsafety-checking `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { true }
     }
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index 2e8b6c19ec7..b4a02fae454 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -14,7 +14,7 @@ use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
 use rustc_session::lint::Level;
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::symbol::Symbol;
-use rustc_span::Span;
+use rustc_span::{sym, Span};
 
 use std::mem;
 use std::ops::Bound;
@@ -144,11 +144,17 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
             let hir_context = self.tcx.local_def_id_to_hir_id(def);
             let safety_context = mem::replace(&mut self.safety_context, SafetyContext::Safe);
             let mut inner_visitor = UnsafetyVisitor {
+                tcx: self.tcx,
                 thir: inner_thir,
                 hir_context,
                 safety_context,
+                body_target_features: self.body_target_features,
+                assignment_info: self.assignment_info,
+                in_union_destructure: false,
+                param_env: self.param_env,
+                inside_adt: false,
                 warnings: self.warnings,
-                ..*self
+                suggest_unsafe_block: self.suggest_unsafe_block,
             };
             inner_visitor.visit_expr(&inner_thir[expr]);
             // Unsafe blocks can be used in the inner body, make sure to take it into account
@@ -886,14 +892,15 @@ impl UnsafeOpKind {
     }
 }
 
-pub fn thir_check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
-    // THIR unsafeck is gated under `-Z thir-unsafeck`
+pub fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
+    // THIR unsafeck can be disabled with `-Z thir-unsafeck=off`
     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
         return;
     }
 
     // Closures and inline consts are handled by their owner, if it has a body
-    if tcx.is_typeck_child(def.to_def_id()) {
+    // Also, don't safety check custom MIR
+    if tcx.is_typeck_child(def.to_def_id()) || tcx.has_attr(def, sym::custom_mir) {
         return;
     }
 
diff --git a/compiler/rustc_mir_build/src/lib.rs b/compiler/rustc_mir_build/src/lib.rs
index a776e917de5..430c4ee3da7 100644
--- a/compiler/rustc_mir_build/src/lib.rs
+++ b/compiler/rustc_mir_build/src/lib.rs
@@ -31,7 +31,7 @@ pub fn provide(providers: &mut Providers) {
     providers.mir_built = build::mir_built;
     providers.closure_saved_names_of_captured_variables =
         build::closure_saved_names_of_captured_variables;
-    providers.thir_check_unsafety = check_unsafety::thir_check_unsafety;
+    providers.check_unsafety = check_unsafety::check_unsafety;
     providers.thir_body = thir::cx::thir_body;
     providers.thir_tree = thir::print::thir_tree;
     providers.thir_flat = thir::print::thir_flat;
diff --git a/compiler/rustc_mir_transform/src/check_unsafety.rs b/compiler/rustc_mir_transform/src/check_unsafety.rs
index d94d96c1115..582c2c0c6b6 100644
--- a/compiler/rustc_mir_transform/src/check_unsafety.rs
+++ b/compiler/rustc_mir_transform/src/check_unsafety.rs
@@ -131,7 +131,7 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Coroutine(def_id, _) => {
                     let def_id = def_id.expect_local();
                     let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
-                        self.tcx.unsafety_check_result(def_id);
+                        self.tcx.mir_unsafety_check_result(def_id);
                     self.register_violations(violations, used_unsafe_blocks.items().copied());
                 }
             },
@@ -153,7 +153,7 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
                     if self.tcx.def_kind(def_id) == DefKind::InlineConst {
                         let local_def_id = def_id.expect_local();
                         let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
-                            self.tcx.unsafety_check_result(local_def_id);
+                            self.tcx.mir_unsafety_check_result(local_def_id);
                         self.register_violations(violations, used_unsafe_blocks.items().copied());
                     }
                 }
@@ -390,7 +390,7 @@ impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 }
 
 pub(crate) fn provide(providers: &mut Providers) {
-    *providers = Providers { unsafety_check_result, ..*providers };
+    *providers = Providers { mir_unsafety_check_result, ..*providers };
 }
 
 /// Context information for [`UnusedUnsafeVisitor`] traversal,
@@ -490,7 +490,7 @@ fn check_unused_unsafe(
     unused_unsafes
 }
 
-fn unsafety_check_result(tcx: TyCtxt<'_>, def: LocalDefId) -> &UnsafetyCheckResult {
+fn mir_unsafety_check_result(tcx: TyCtxt<'_>, def: LocalDefId) -> &UnsafetyCheckResult {
     debug!("unsafety_violations({:?})", def);
 
     // N.B., this borrow is valid because all the consumers of
@@ -538,7 +538,8 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
         return;
     }
 
-    let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
+    let UnsafetyCheckResult { violations, unused_unsafes, .. } =
+        tcx.mir_unsafety_check_result(def_id);
     // Only suggest wrapping the entire function body in an unsafe block once
     let mut suggest_unsafe_block = true;
 
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 5562ae7f3bd..164b6b9c4f5 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -285,9 +285,9 @@ fn mir_const_qualif(tcx: TyCtxt<'_>, def: LocalDefId) -> ConstQualifs {
 /// FIXME(oli-obk): it's unclear whether we still need this phase (and its corresponding query).
 /// We used to have this for pre-miri MIR based const eval.
 fn mir_const(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
-    // Unsafety check uses the raw mir, so make sure it is run.
+    // MIR unsafety check uses the raw mir, so make sure it is run.
     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
-        tcx.ensure_with_value().unsafety_check_result(def);
+        tcx.ensure_with_value().mir_unsafety_check_result(def);
     }
 
     // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 8274fd05bc0..0b0b67ef890 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1919,8 +1919,8 @@ written to standard error output)"),
     #[rustc_lint_opt_deny_field_access("use `Session::lto` instead of this field")]
     thinlto: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "enable ThinLTO when possible"),
-    thir_unsafeck: bool = (false, parse_bool, [TRACKED],
-        "use the THIR unsafety checker (default: no)"),
+    thir_unsafeck: bool = (true, parse_bool, [TRACKED],
+        "use the THIR unsafety checker (default: yes)"),
     /// We default to 1 here since we want to behave like
     /// a sequential compiler for now. This'll likely be adjusted
     /// in the future. Note that -Zthreads=0 is the way to get