handle nested generics in Generics::type_param/region_param

Fixes #44952.

src/librustc/infer/error_reporting/mod.rs

@@ -795,7 +795,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     // Account for the case where `did` corresponds to `Self`, which doesn't have
                     // the expected type argument.
                     if generics.types.len() > 0 {
-                        let type_param = generics.type_param(param);
+                        let type_param = generics.type_param(param, self.tcx);
                         let hir = &self.tcx.hir;
                         hir.as_local_node_id(type_param.def_id).map(|id| {
                             // Get the `hir::TyParam` to verify wether it already has any bounds.

src/librustc/ty/mod.rs

@@ -729,7 +729,7 @@ pub struct Generics {
     pub has_late_bound_regions: Option<Span>,
 }
 
-impl Generics {
+impl<'a, 'gcx, 'tcx> Generics {
     pub fn parent_count(&self) -> usize {
         self.parent_regions as usize + self.parent_types as usize
     }
@@ -742,14 +742,28 @@ impl Generics {
         self.parent_count() + self.own_count()
     }
 
-    pub fn region_param(&self, param: &EarlyBoundRegion) -> &RegionParameterDef {
-        assert_eq!(self.parent_count(), 0);
-        &self.regions[param.index as usize - self.has_self as usize]
+    pub fn region_param(&'tcx self,
+                        param: &EarlyBoundRegion,
+                        tcx: TyCtxt<'a, 'gcx, 'tcx>)
+                        -> &'tcx RegionParameterDef
+    {
+        if let Some(index) = param.index.checked_sub(self.parent_count() as u32) {
+            &self.regions[index as usize - self.has_self as usize]
+        } else {
+            tcx.generics_of(self.parent.expect("parent_count>0 but no parent?"))
+                .region_param(param, tcx)
+        }
     }
 
-    pub fn type_param(&self, param: &ParamTy) -> &TypeParameterDef {
-        assert_eq!(self.parent_count(), 0);
-        &self.types[param.idx as usize - self.has_self as usize - self.regions.len()]
+    pub fn type_param(&'tcx self,
+                      param: &ParamTy,
+                      tcx: TyCtxt<'a, 'gcx, 'tcx>) -> &TypeParameterDef {
+        if let Some(idx) = param.idx.checked_sub(self.parent_count() as u32) {
+            &self.types[idx as usize - self.has_self as usize - self.regions.len()]
+        } else {
+            tcx.generics_of(self.parent.expect("parent_count>0 but no parent?"))
+                .type_param(param, tcx)
+        }
     }
 }
 

src/librustc/ty/util.rs

@@ -515,11 +515,11 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         let result = item_substs.iter().zip(impl_substs.iter())
             .filter(|&(_, &k)| {
                 if let Some(&ty::RegionKind::ReEarlyBound(ref ebr)) = k.as_region() {
-                    !impl_generics.region_param(ebr).pure_wrt_drop
+                    !impl_generics.region_param(ebr, self).pure_wrt_drop
                 } else if let Some(&ty::TyS {
                     sty: ty::TypeVariants::TyParam(ref pt), ..
                 }) = k.as_type() {
-                    !impl_generics.type_param(pt).pure_wrt_drop
+                    !impl_generics.type_param(pt, self).pure_wrt_drop
                 } else {
                     // not a type or region param - this should be reported
                     // as an error.

src/test/ui/lifetimes/lifetime-doesnt-live-long-enough.rs

@@ -28,4 +28,14 @@ struct Foo<T> {
     foo: &'static T
 }
 
+trait X<T> {}
+
+struct Nested<K>(K);
+impl<K> Nested<K> {
+    fn generic_in_parent<'a, L: X<&'a Nested<K>>>() {
+    }
+    fn generic_in_child<'a, 'b, L: X<&'a Nested<M>>, M: 'b>() {
+    }
+}
+
 fn main() {}

src/test/ui/lifetimes/lifetime-doesnt-live-long-enough.stderr

@@ -26,5 +26,38 @@ note: ...so that the reference type `&'static T` does not outlive the data it po
 28 |     foo: &'static T
    |     ^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error[E0309]: the parameter type `K` may not live long enough
+  --> $DIR/lifetime-doesnt-live-long-enough.rs:35:5
+   |
+34 |   impl<K> Nested<K> {
+   |        - help: consider adding an explicit lifetime bound `K: 'a`...
+35 | /     fn generic_in_parent<'a, L: X<&'a Nested<K>>>() {
+36 | |     }
+   | |_____^
+   |
+note: ...so that the reference type `&'a Nested<K>` does not outlive the data it points at
+  --> $DIR/lifetime-doesnt-live-long-enough.rs:35:5
+   |
+35 | /     fn generic_in_parent<'a, L: X<&'a Nested<K>>>() {
+36 | |     }
+   | |_____^
+
+error[E0309]: the parameter type `M` may not live long enough
+  --> $DIR/lifetime-doesnt-live-long-enough.rs:37:5
+   |
+37 |       fn generic_in_child<'a, 'b, L: X<&'a Nested<M>>, M: 'b>() {
+   |       ^                                                -- help: consider adding an explicit lifetime bound `M: 'a`...
+   |  _____|
+   | |
+38 | |     }
+   | |_____^
+   |
+note: ...so that the reference type `&'a Nested<M>` does not outlive the data it points at
+  --> $DIR/lifetime-doesnt-live-long-enough.rs:37:5
+   |
+37 | /     fn generic_in_child<'a, 'b, L: X<&'a Nested<M>>, M: 'b>() {
+38 | |     }
+   | |_____^
+
+error: aborting due to 4 previous errors