Auto merge of #75260 - davidtwco:polymorphization-promoted-substs, r=lcnr

polymorphize: unevaluated constants

This PR makes polymorphization visit the promoted MIR of unevaluated constants with available promoted MIR instead of visiting the substitutions of that constant - which will mark all of the generic parameters as used; in addition polymorphization will now visit non-promoted unevaluated constants rather than visit their substs.

r? @lcnr

src/librustc_mir/monomorphize/polymorphize.rs

@@ -15,6 +15,7 @@ use rustc_middle::ty::{
     self,
     fold::{TypeFoldable, TypeVisitor},
     query::Providers,
+    subst::SubstsRef,
     Const, Ty, TyCtxt,
 };
 use rustc_span::symbol::sym;
@@ -209,6 +210,25 @@ struct UsedGenericParametersVisitor<'a, 'tcx> {
     unused_parameters: &'a mut FiniteBitSet<u32>,
 }
 
+impl<'a, 'tcx> UsedGenericParametersVisitor<'a, 'tcx> {
+    /// Invoke `unused_generic_params` on a body contained within the current item (e.g.
+    /// a closure, generator or constant).
+    fn visit_child_body(&mut self, def_id: DefId, substs: SubstsRef<'tcx>) {
+        let unused = self.tcx.unused_generic_params(def_id);
+        debug!(
+            "visit_child_body: unused_parameters={:?} unused={:?}",
+            self.unused_parameters, unused
+        );
+        for (i, arg) in substs.iter().enumerate() {
+            let i = i.try_into().unwrap();
+            if !unused.contains(i).unwrap_or(false) {
+                arg.visit_with(self);
+            }
+        }
+        debug!("visit_child_body: unused_parameters={:?}", self.unused_parameters);
+    }
+}
+
 impl<'a, 'tcx> Visitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
         debug!("visit_local_decl: local_decl={:?}", local_decl);
@@ -249,6 +269,17 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
                 self.unused_parameters.clear(param.index);
                 false
             }
+            ty::ConstKind::Unevaluated(_, _, Some(p)) => {
+                // If there is a promoted, don't look at the substs - since it will always contain
+                // the generic parameters, instead, traverse the promoted MIR.
+                let promoted = self.tcx.promoted_mir(self.def_id);
+                self.visit_body(&promoted[p]);
+                false
+            }
+            ty::ConstKind::Unevaluated(def_id, unevaluated_substs, None) => {
+                self.visit_child_body(def_id.did, unevaluated_substs);
+                false
+            }
             _ => c.super_visit_with(self),
         }
     }
@@ -269,19 +300,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UsedGenericParametersVisitor<'a, 'tcx> {
 
                 // Consider any generic parameters used by any closures/generators as used in the
                 // parent.
-                let unused = self.tcx.unused_generic_params(def_id);
-                debug!(
-                    "visit_ty: unused_parameters={:?} unused={:?}",
-                    self.unused_parameters, unused
-                );
-                for (i, arg) in substs.iter().enumerate() {
-                    let i = i.try_into().unwrap();
-                    if !unused.contains(i).unwrap_or(false) {
-                        arg.visit_with(self);
-                    }
-                }
-                debug!("visit_ty: unused_parameters={:?}", self.unused_parameters);
-
+                self.visit_child_body(def_id, substs);
                 false
             }
             ty::Param(param) => {

src/test/ui/polymorphization/promoted-function-1.rs

@@ -0,0 +1,12 @@
+// build-fail
+// compile-flags: -Zpolymorphize=on
+#![crate_type = "lib"]
+#![feature(rustc_attrs)]
+
+fn foo<'a>(_: &'a ()) {}
+
+#[rustc_polymorphize_error]
+pub fn test<T>() {
+    //~^ ERROR item has unused generic parameters
+    foo(&());
+}

src/test/ui/polymorphization/promoted-function-1.stderr

@@ -0,0 +1,8 @@
+error: item has unused generic parameters
+  --> $DIR/promoted-function-1.rs:9:8
+   |
+LL | pub fn test<T>() {
+   |        ^^^^ - generic parameter `T` is unused
+
+error: aborting due to previous error
+

src/test/ui/polymorphization/promoted-function-2.rs

@@ -0,0 +1,16 @@
+// build-fail
+// compile-flags:-Zpolymorphize=on
+#![crate_type = "lib"]
+#![feature(lazy_normalization_consts, rustc_attrs)]
+//~^ WARN the feature `lazy_normalization_consts` is incomplete
+
+#[rustc_polymorphize_error]
+fn test<T>() {
+    //~^ ERROR item has unused generic parameters
+    let x = [0; 3 + 4];
+}
+
+pub fn caller() {
+    test::<String>();
+    test::<Vec<String>>();
+}

src/test/ui/polymorphization/promoted-function-2.stderr

@@ -0,0 +1,17 @@
+warning: the feature `lazy_normalization_consts` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/promoted-function-2.rs:4:12
+   |
+LL | #![feature(lazy_normalization_consts, rustc_attrs)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #72219 <https://github.com/rust-lang/rust/issues/72219> for more information
+
+error: item has unused generic parameters
+  --> $DIR/promoted-function-2.rs:8:4
+   |
+LL | fn test<T>() {
+   |    ^^^^ - generic parameter `T` is unused
+
+error: aborting due to previous error; 1 warning emitted
+

src/test/ui/polymorphization/promoted-function.rs

@@ -1,4 +1,6 @@
 // run-pass
+// compile-flags:-Zpolymorphize=on
+
 fn fop<T>() {}
 
 fn bar<T>() -> &'static fn() {

src/test/ui/polymorphization/unsized_cast.rs

@@ -17,6 +17,7 @@ fn foo<T: Default>() {
 fn foo2<T: Default>() {
     let _: T = Default::default();
     (|| {
+        //~^ ERROR item has unused generic parameters
         let call: extern "rust-call" fn(_, _) = Fn::call;
         call(&|| {}, ());
         //~^ ERROR item has unused generic parameters

src/test/ui/polymorphization/unsized_cast.stderr

@@ -17,7 +17,7 @@ LL |     (|| Box::new(|| {}) as Box<dyn Fn()>)();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: item has unused generic parameters
-  --> $DIR/unsized_cast.rs:21:15
+  --> $DIR/unsized_cast.rs:22:15
    |
 LL | fn foo2<T: Default>() {
    |         - generic parameter `T` is unused
@@ -25,5 +25,19 @@ LL | fn foo2<T: Default>() {
 LL |         call(&|| {}, ());
    |               ^^^^^
 
-error: aborting due to 3 previous errors
+error: item has unused generic parameters
+  --> $DIR/unsized_cast.rs:19:5
+   |
+LL |   fn foo2<T: Default>() {
+   |           - generic parameter `T` is unused
+LL |       let _: T = Default::default();
+LL | /     (|| {
+LL | |
+LL | |         let call: extern "rust-call" fn(_, _) = Fn::call;
+LL | |         call(&|| {}, ());
+LL | |
+LL | |     })();
+   | |______^
+
+error: aborting due to 4 previous errors