diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index c343809179b0a..f10efd832361c 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -157,6 +157,7 @@ E0308: include_str!("./error_codes/E0308.md"),
 E0309: include_str!("./error_codes/E0309.md"),
 E0310: include_str!("./error_codes/E0310.md"),
 E0312: include_str!("./error_codes/E0312.md"),
+E0316: include_str!("./error_codes/E0316.md"),
 E0317: include_str!("./error_codes/E0317.md"),
 E0321: include_str!("./error_codes/E0321.md"),
 E0322: include_str!("./error_codes/E0322.md"),
@@ -553,9 +554,8 @@ E0783: include_str!("./error_codes/E0783.md"),
     E0311, // thing may not live long enough
     E0313, // lifetime of borrowed pointer outlives lifetime of captured
            // variable
-    E0314, // closure outlives stack frame
-    E0315, // cannot invoke closure outside of its lifetime
-    E0316, // nested quantification of lifetimes
+//  E0314, // closure outlives stack frame
+//  E0315, // cannot invoke closure outside of its lifetime
 //  E0319, // trait impls for defaulted traits allowed just for structs/enums
     E0320, // recursive overflow during dropck
 //  E0372, // coherence not object safe
@@ -584,21 +584,21 @@ E0783: include_str!("./error_codes/E0783.md"),
 //  E0470, removed
 //  E0471, // constant evaluation error (in pattern)
     E0472, // llvm_asm! is unsupported on this target
-    E0473, // dereference of reference outside its lifetime
-    E0474, // captured variable `..` does not outlive the enclosing closure
-    E0475, // index of slice outside its lifetime
+//  E0473, // dereference of reference outside its lifetime
+//  E0474, // captured variable `..` does not outlive the enclosing closure
+//  E0475, // index of slice outside its lifetime
     E0476, // lifetime of the source pointer does not outlive lifetime bound...
-    E0479, // the type `..` (provided as the value of a type parameter) is...
-    E0480, // lifetime of method receiver does not outlive the method call
-    E0481, // lifetime of function argument does not outlive the function call
+//  E0479, // the type `..` (provided as the value of a type parameter) is...
+//  E0480, // lifetime of method receiver does not outlive the method call
+//  E0481, // lifetime of function argument does not outlive the function call
     E0482, // lifetime of return value does not outlive the function call
-    E0483, // lifetime of operand does not outlive the operation
-    E0484, // reference is not valid at the time of borrow
-    E0485, // automatically reference is not valid at the time of borrow
-    E0486, // type of expression contains references that are not valid during..
-    E0487, // unsafe use of destructor: destructor might be called while...
-    E0488, // lifetime of variable does not enclose its declaration
-    E0489, // type/lifetime parameter not in scope here
+//  E0483, // lifetime of operand does not outlive the operation
+//  E0484, // reference is not valid at the time of borrow
+//  E0485, // automatically reference is not valid at the time of borrow
+//  E0486, // type of expression contains references that are not valid during..
+//  E0487, // unsafe use of destructor: destructor might be called while...
+//  E0488, // lifetime of variable does not enclose its declaration
+//  E0489, // type/lifetime parameter not in scope here
     E0490, // a value of type `..` is borrowed for too long
     E0498,  // malformed plugin attribute
     E0514, // metadata version mismatch
diff --git a/compiler/rustc_error_codes/src/error_codes/E0316.md b/compiler/rustc_error_codes/src/error_codes/E0316.md
new file mode 100644
index 0000000000000..4368c321737b2
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0316.md
@@ -0,0 +1,32 @@
+A `where` clause contains a nested quantification over lifetimes.
+
+Erroneous code example:
+
+```compile_fail,E0316
+trait Tr<'a, 'b> {}
+
+fn foo<T>(t: T)
+where
+    for<'a> &'a T: for<'b> Tr<'a, 'b>, // error: nested quantification
+{
+}
+```
+
+Rust syntax allows lifetime quantifications in two places within
+`where` clauses: Quantifying over the trait bound only (as in
+`Ty: for<'l> Trait<'l>`) and quantifying over the whole clause
+(as in `for<'l> &'l Ty: Trait<'l>`). Using both in the same clause
+leads to a nested lifetime quantification, which is not supported.
+
+The following example compiles, because the clause with the nested
+quantification has been rewritten to use only one `for<>`:
+
+```
+trait Tr<'a, 'b> {}
+
+fn foo<T>(t: T)
+where
+    for<'a, 'b> &'a T: Tr<'a, 'b>, // ok
+{
+}
+```
diff --git a/compiler/rustc_resolve/src/late/lifetimes.rs b/compiler/rustc_resolve/src/late/lifetimes.rs
index efa5d7e7b1139..ca7cdc4caf505 100644
--- a/compiler/rustc_resolve/src/late/lifetimes.rs
+++ b/compiler/rustc_resolve/src/late/lifetimes.rs
@@ -1841,14 +1841,6 @@ fn object_lifetime_defaults_for_item(
 }
 
 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
-    // FIXME(#37666) this works around a limitation in the region inferencer
-    fn hack<F>(&mut self, f: F)
-    where
-        F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
-    {
-        f(self)
-    }
-
     fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
     where
         F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
@@ -2252,7 +2244,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
         };
         self.with(scope, move |old_scope, this| {
             this.check_lifetime_params(old_scope, &generics.params);
-            this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
+            walk(this);
         });
     }
 
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
index 02957e75a7409..e591e073e7bbb 100644
--- a/library/std/src/panicking.rs
+++ b/library/std/src/panicking.rs
@@ -193,7 +193,7 @@ fn default_hook(info: &PanicInfo<'_>) {
         Some(s) => *s,
         None => match info.payload().downcast_ref::<String>() {
             Some(s) => &s[..],
-            None => "Box<Any>",
+            None => "Box<dyn Any>",
         },
     };
     let thread = thread_info::current_thread();
diff --git a/src/librustdoc/clean/auto_trait.rs b/src/librustdoc/clean/auto_trait.rs
index 35ff57f85a562..a3f63ea1046e3 100644
--- a/src/librustdoc/clean/auto_trait.rs
+++ b/src/librustdoc/clean/auto_trait.rs
@@ -664,7 +664,10 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                     }
                 }
                 GenericParamDefKind::Lifetime => {}
-                GenericParamDefKind::Const { .. } => {}
+                GenericParamDefKind::Const { ref mut default, .. } => {
+                    // We never want something like `impl<const N: usize = 10>`
+                    default.take();
+                }
             }
         }
 
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 231f13adeb68c..d1c18821ea644 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -445,11 +445,15 @@ impl Clean<GenericParamDef> for ty::GenericParamDef {
                     },
                 )
             }
-            ty::GenericParamDefKind::Const { .. } => (
+            ty::GenericParamDefKind::Const { has_default, .. } => (
                 self.name,
                 GenericParamDefKind::Const {
                     did: self.def_id,
                     ty: cx.tcx.type_of(self.def_id).clean(cx),
+                    default: match has_default {
+                        true => Some(cx.tcx.const_param_default(self.def_id).to_string()),
+                        false => None,
+                    },
                 },
             ),
         };
@@ -487,12 +491,15 @@ impl Clean<GenericParamDef> for hir::GenericParam<'_> {
                     synthetic,
                 },
             ),
-            hir::GenericParamKind::Const { ref ty, default: _ } => (
+            hir::GenericParamKind::Const { ref ty, default } => (
                 self.name.ident().name,
                 GenericParamDefKind::Const {
                     did: cx.tcx.hir().local_def_id(self.hir_id).to_def_id(),
                     ty: ty.clean(cx),
-                    // FIXME(const_generics_defaults): add `default` field here for docs
+                    default: default.map(|ct| {
+                        let def_id = cx.tcx.hir().local_def_id(ct.hir_id);
+                        ty::Const::from_anon_const(cx.tcx, def_id).to_string()
+                    }),
                 },
             ),
         };
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index fa1639f9dc3dd..6a7c3f8caa49f 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -1220,6 +1220,7 @@ crate enum GenericParamDefKind {
     Const {
         did: DefId,
         ty: Type,
+        default: Option<String>,
     },
 }
 
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index d5213fd77117a..918a5cb509430 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -177,12 +177,22 @@ impl clean::GenericParamDef {
 
                 Ok(())
             }
-            clean::GenericParamDefKind::Const { ref ty, .. } => {
+            clean::GenericParamDefKind::Const { ref ty, ref default, .. } => {
                 if f.alternate() {
-                    write!(f, "const {}: {:#}", self.name, ty.print(cx))
+                    write!(f, "const {}: {:#}", self.name, ty.print(cx))?;
                 } else {
-                    write!(f, "const {}:&nbsp;{}", self.name, ty.print(cx))
+                    write!(f, "const {}:&nbsp;{}", self.name, ty.print(cx))?;
                 }
+
+                if let Some(default) = default {
+                    if f.alternate() {
+                        write!(f, " = {:#}", default)?;
+                    } else {
+                        write!(f, "&nbsp;=&nbsp;{}", default)?;
+                    }
+                }
+
+                Ok(())
             }
         })
     }
diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index 578e8ce5acbef..d8684641a3045 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -138,7 +138,7 @@ h2, h3, h4 {
 	border-bottom: 1px solid;
 }
 .impl, .method,
-.type, .associatedconstant,
+.type:not(.container-rustdoc), .associatedconstant,
 .associatedtype {
 	flex-basis: 100%;
 	font-weight: 600;
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index bee62915ea9b1..7086dd8c4d258 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -317,7 +317,9 @@ impl FromWithTcx<clean::GenericParamDefKind> for GenericParamDefKind {
                 bounds: bounds.into_iter().map(|x| x.into_tcx(tcx)).collect(),
                 default: default.map(|x| x.into_tcx(tcx)),
             },
-            Const { did: _, ty } => GenericParamDefKind::Const(ty.into_tcx(tcx)),
+            Const { did: _, ty, default } => {
+                GenericParamDefKind::Const { ty: ty.into_tcx(tcx), default }
+            }
         }
     }
 }
diff --git a/src/librustdoc/json/mod.rs b/src/librustdoc/json/mod.rs
index f8bd971081395..0d84bf250c9e3 100644
--- a/src/librustdoc/json/mod.rs
+++ b/src/librustdoc/json/mod.rs
@@ -234,7 +234,7 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
                     )
                 })
                 .collect(),
-            format_version: 5,
+            format_version: 6,
         };
         let mut p = self.out_path.clone();
         p.push(output.index.get(&output.root).unwrap().name.clone().unwrap());
diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
index 72a4d9a183011..6d9a5cb515a48 100644
--- a/src/rustdoc-json-types/lib.rs
+++ b/src/rustdoc-json-types/lib.rs
@@ -324,7 +324,7 @@ pub struct GenericParamDef {
 pub enum GenericParamDefKind {
     Lifetime,
     Type { bounds: Vec<GenericBound>, default: Option<Type> },
-    Const(Type),
+    Const { ty: Type, default: Option<String> },
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
diff --git a/src/test/rustdoc-gui/sidebar.goml b/src/test/rustdoc-gui/sidebar.goml
index 388ca120d770e..7703677154ef9 100644
--- a/src/test/rustdoc-gui/sidebar.goml
+++ b/src/test/rustdoc-gui/sidebar.goml
@@ -11,7 +11,8 @@ assert: (".sidebar-elems > .items > ul > li:nth-child(2)", "Structs")
 assert: (".sidebar-elems > .items > ul > li:nth-child(3)", "Enums")
 assert: (".sidebar-elems > .items > ul > li:nth-child(4)", "Traits")
 assert: (".sidebar-elems > .items > ul > li:nth-child(5)", "Functions")
-assert: (".sidebar-elems > .items > ul > li:nth-child(6)", "Keywords")
+assert: (".sidebar-elems > .items > ul > li:nth-child(6)", "Type Definitions")
+assert: (".sidebar-elems > .items > ul > li:nth-child(7)", "Keywords")
 assert: ("#structs + table td > a", "Foo")
 click: "#structs + table td > a"
 
diff --git a/src/test/rustdoc-gui/src/lib.rs b/src/test/rustdoc-gui/src/lib.rs
index 272b1d05452e3..5141b6d1920ea 100644
--- a/src/test/rustdoc-gui/src/lib.rs
+++ b/src/test/rustdoc-gui/src/lib.rs
@@ -96,3 +96,6 @@ pub enum AnEnum {
 
 #[doc(keyword = "CookieMonster")]
 pub mod keyword {}
+
+/// Just some type alias.
+pub type SomeType = u32;
diff --git a/src/test/rustdoc-gui/type-weight.rs b/src/test/rustdoc-gui/type-weight.rs
new file mode 100644
index 0000000000000..8b6518e7f317a
--- /dev/null
+++ b/src/test/rustdoc-gui/type-weight.rs
@@ -0,0 +1,2 @@
+goto: file://|DOC_PATH|/test_docs/type.SomeType.html
+assert-all: (".top-block .docblock p", {"font-weight": "400"})
diff --git a/src/test/rustdoc/const-generics/const-generic-defaults.rs b/src/test/rustdoc/const-generics/const-generic-defaults.rs
new file mode 100644
index 0000000000000..efe35bf7aa442
--- /dev/null
+++ b/src/test/rustdoc/const-generics/const-generic-defaults.rs
@@ -0,0 +1,6 @@
+#![crate_name = "foo"]
+#![feature(const_generics_defaults)]
+
+// @has foo/struct.Foo.html '//pre[@class="rust struct"]' \
+//      'pub struct Foo<const M: usize = 10_usize, const N: usize = M, T = i32>(_);'
+pub struct Foo<const M: usize = 10, const N: usize = M, T = i32>(T);
diff --git a/src/test/ui/panics/panic-macro-any-wrapped.rs b/src/test/ui/panics/panic-macro-any-wrapped.rs
index 95ae6ffe8be02..100ac10c76717 100644
--- a/src/test/ui/panics/panic-macro-any-wrapped.rs
+++ b/src/test/ui/panics/panic-macro-any-wrapped.rs
@@ -1,5 +1,5 @@
 // run-fail
-// error-pattern:panicked at 'Box<Any>'
+// error-pattern:panicked at 'Box<dyn Any>'
 // ignore-emscripten no processes
 
 #![allow(non_fmt_panic)]
diff --git a/src/test/ui/panics/panic-macro-any.rs b/src/test/ui/panics/panic-macro-any.rs
index d2a7ba3713a51..a5ba30220e89a 100644
--- a/src/test/ui/panics/panic-macro-any.rs
+++ b/src/test/ui/panics/panic-macro-any.rs
@@ -1,5 +1,5 @@
 // run-fail
-// error-pattern:panicked at 'Box<Any>'
+// error-pattern:panicked at 'Box<dyn Any>'
 // ignore-emscripten no processes
 
 #![feature(box_syntax)]
diff --git a/src/test/ui/where-clauses/where-for-self.stderr b/src/test/ui/where-clauses/where-for-self.stderr
index 84430ffcf887f..d06afc1e42376 100644
--- a/src/test/ui/where-clauses/where-for-self.stderr
+++ b/src/test/ui/where-clauses/where-for-self.stderr
@@ -6,3 +6,4 @@ LL |     where for<'a> &'a T: for<'b> Bar<'b>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0316`.