Partial preparations for upgrading to Rust nightly-2020-05-26

CC #26661
Fixes #26645

components/derive_common/cg.rs

@@ -7,7 +7,7 @@ use proc_macro2::{Span, TokenStream};
 use quote::TokenStreamExt;
 use syn::{self, AngleBracketedGenericArguments, Binding, DeriveInput, Field};
 use syn::{GenericArgument, GenericParam, Ident, Path};
-use syn::{PathArguments, PathSegment, QSelf, Type, TypeArray};
+use syn::{PathArguments, PathSegment, QSelf, Type, TypeArray, TypeGroup};
 use syn::{TypeParam, TypeParen, TypePath, TypeSlice, TypeTuple};
 use syn::{Variant, WherePredicate};
 use synstructure::{self, BindStyle, BindingInfo, VariantAst, VariantInfo};
@@ -187,6 +187,10 @@ where
             elem: Box::new(map_type_params(&inner.elem, params, f)),
             ..inner.clone()
         }),
+        Type::Group(ref inner) => Type::from(TypeGroup {
+            elem: Box::new(map_type_params(&inner.elem, params, f)),
+            ..inner.clone()
+        }),
         ref ty => panic!("type {:?} cannot be mapped yet", ty),
     }
 }

python/servo/command_base.py

@@ -986,7 +986,13 @@ def ensure_bootstrapped(self, target=None, rustup_components=None):
             installed = check_output(
                 ["rustup", "component", "list", "--installed", "--toolchain", toolchain]
             )
-            for component in set(rustup_components or []) | {"rustc-dev"}:
+            required_components = {
+                # For components/script_plugins, https://github.com/rust-lang/rust/pull/67469
+                "rustc-dev",
+                # https://github.com/rust-lang/rust/issues/72594#issuecomment-633779564
+                "llvm-tools-preview",
+            }
+            for component in set(rustup_components or []) | required_components:
                 if component.encode("utf-8") not in installed:
                     check_call(["rustup", "component", "add", "--toolchain", toolchain, component])