borrowck: wf-check fn item substs

Author: aliemjay

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -427,14 +427,24 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                 // const_trait_impl: use a non-const param env when checking that a FnDef type is well formed.
                 // this is because the well-formedness of the function does not need to be proved to have `const`
                 // impls for trait bounds.
-                let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
                 let prev = self.cx.param_env;
                 self.cx.param_env = prev.without_const();
+
+                let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
                 self.cx.normalize_and_prove_instantiated_predicates(
                     def_id,
                     instantiated_predicates,
                     locations,
                 );
+
+                self.cx.prove_predicates(
+                    substs
+                        .types()
+                        .map(|ty| ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))),
+                    locations,
+                    ConstraintCategory::Boring,
+                );
+
                 self.cx.param_env = prev;
             }
         }

library/std/src/collections/hash/map.rs

@@ -3051,8 +3051,8 @@ where
 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
 where
-    K: Eq + Hash + Copy,
-    V: Copy,
+    K: Eq + Hash + Copy + 'a,
+    V: Copy + 'a,
     S: BuildHasher,
 {
     #[inline]

src/test/ui/borrowck/fn-item-check-trait-ref.rs

@@ -0,0 +1,15 @@
+// The method `assert_static` should be callable only for static values,
+// because the impl has an implied bound `where T: 'static`.
+
+// check-fail
+
+trait AnyStatic<Witness>: Sized {
+    fn assert_static(self) {}
+}
+
+impl<T> AnyStatic<&'static T> for T {}
+
+fn main() {
+    (&String::new()).assert_static();
+    //~^ ERROR temporary value dropped while borrowed
+}

src/test/ui/borrowck/fn-item-check-trait-ref.stderr

@@ -0,0 +1,12 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/fn-item-check-trait-ref.rs:13:7
+   |
+LL |     (&String::new()).assert_static();
+   |     --^^^^^^^^^^^^^------------------ temporary value is freed at the end of this statement
+   |     | |
+   |     | creates a temporary which is freed while still in use
+   |     argument requires that borrow lasts for `'static`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0716`.

src/test/ui/borrowck/fn-item-check-type-params.rs

@@ -0,0 +1,57 @@
+// Regression test for #104005.
+//
+// Previously, different borrowck implementations used to disagree here.
+// The status of each is documented on `fn test_*`.
+
+// check-fail
+
+use std::fmt::Display;
+
+trait Displayable {
+    fn display(self) -> Box<dyn Display>;
+}
+
+impl<T: Display> Displayable for (T, Option<&'static T>) {
+    fn display(self) -> Box<dyn Display> {
+        Box::new(self.0)
+    }
+}
+
+fn extend_lt<T, U>(val: T) -> Box<dyn Display>
+where
+    (T, Option<U>): Displayable,
+{
+    Displayable::display((val, None))
+}
+
+// AST: fail
+// HIR: pass
+// MIR: pass
+pub fn test_call<'a>(val: &'a str) {
+    extend_lt(val);
+    //~^ ERROR borrowed data escapes outside of function
+}
+
+// AST: fail
+// HIR: fail
+// MIR: pass
+pub fn test_coercion<'a>() {
+    let _: fn(&'a str) -> _ = extend_lt;
+    //~^ ERROR lifetime may not live long enough
+}
+
+// AST: fail
+// HIR: fail
+// MIR: fail
+pub fn test_arg() {
+    fn want<I, O>(_: I, _: impl Fn(I) -> O) {}
+    want(&String::new(), extend_lt);
+    //~^ ERROR temporary value dropped while borrowed
+}
+
+// An exploit of the unsoundness.
+fn main() {
+    let val = extend_lt(&String::from("blah blah blah"));
+    //~^ ERROR temporary value dropped while borrowed
+    println!("{}", val);
+}

src/test/ui/borrowck/fn-item-check-type-params.stderr

@@ -0,0 +1,43 @@
+error[E0521]: borrowed data escapes outside of function
+  --> $DIR/fn-item-check-type-params.rs:31:5
+   |
+LL | pub fn test_call<'a>(val: &'a str) {
+   |                  --  --- `val` is a reference that is only valid in the function body
+   |                  |
+   |                  lifetime `'a` defined here
+LL |     extend_lt(val);
+   |     ^^^^^^^^^^^^^^
+   |     |
+   |     `val` escapes the function body here
+   |     argument requires that `'a` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/fn-item-check-type-params.rs:39:12
+   |
+LL | pub fn test_coercion<'a>() {
+   |                      -- lifetime `'a` defined here
+LL |     let _: fn(&'a str) -> _ = extend_lt;
+   |            ^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/fn-item-check-type-params.rs:48:11
+   |
+LL |     want(&String::new(), extend_lt);
+   |     ------^^^^^^^^^^^^^------------- temporary value is freed at the end of this statement
+   |     |     |
+   |     |     creates a temporary which is freed while still in use
+   |     argument requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/fn-item-check-type-params.rs:54:26
+   |
+LL |     let val = extend_lt(&String::from("blah blah blah"));
+   |               -----------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-- temporary value is freed at the end of this statement
+   |               |          |
+   |               |          creates a temporary which is freed while still in use
+   |               argument requires that borrow lasts for `'static`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0521, E0716.
+For more information about an error, try `rustc --explain E0521`.

src/test/ui/higher-rank-trait-bounds/issue-59311.rs

@@ -17,6 +17,7 @@ where
     v.t(|| {});
     //~^ ERROR: higher-ranked lifetime error
     //~| ERROR: higher-ranked lifetime error
+    //~| ERROR: higher-ranked lifetime error
 }
 
 fn main() {}

src/test/ui/higher-rank-trait-bounds/issue-59311.stderr

@@ -6,6 +6,14 @@ LL |     v.t(|| {});
    |
    = note: could not prove `[closure@$DIR/issue-59311.rs:17:9: 17:11] well-formed`
 
+error: higher-ranked lifetime error
+  --> $DIR/issue-59311.rs:17:5
+   |
+LL |     v.t(|| {});
+   |     ^^^^^^^^^^
+   |
+   = note: could not prove `[closure@$DIR/issue-59311.rs:17:9: 17:11] well-formed`
+
 error: higher-ranked lifetime error
   --> $DIR/issue-59311.rs:17:9
    |
@@ -14,5 +22,5 @@ LL |     v.t(|| {});
    |
    = note: could not prove `for<'a> &'a V: 'static`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 

src/test/ui/lifetimes/lifetime-errors/issue_74400.rs

@@ -11,6 +11,8 @@ fn f<T, S>(data: &[T], key: impl Fn(&T) -> S) {
 fn g<T>(data: &[T]) {
     f(data, identity)
     //~^ ERROR the parameter type
+    //~| ERROR the parameter type
+    //~| ERROR the parameter type
     //~| ERROR mismatched types
     //~| ERROR implementation of `FnOnce` is not general
 }

src/test/ui/lifetimes/lifetime-errors/issue_74400.stderr

@@ -9,6 +9,28 @@ help: consider adding an explicit lifetime bound...
 LL | fn g<T: 'static>(data: &[T]) {
    |       +++++++++
 
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL | fn g<T: 'static>(data: &[T]) {
+   |       +++++++++
+
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL | fn g<T: 'static>(data: &[T]) {
+   |       +++++++++
+
 error[E0308]: mismatched types
   --> $DIR/issue_74400.rs:12:5
    |
@@ -32,7 +54,7 @@ LL |     f(data, identity)
    = note: `fn(&'2 T) -> &'2 T {identity::<&'2 T>}` must implement `FnOnce<(&'1 T,)>`, for any lifetime `'1`...
    = note: ...but it actually implements `FnOnce<(&'2 T,)>`, for some specific lifetime `'2`
 
-error: aborting due to 3 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0308, E0310.
 For more information about an error, try `rustc --explain E0308`.