change BuiltinDeriveFn type to get ExtCtxt by immutable ref and fix signatures

compiler/rustc_builtin_macros/src/deriving/bounds.rs

@@ -6,7 +6,7 @@ use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::Span;
 
 pub fn expand_deriving_copy(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,
@@ -29,7 +29,7 @@ pub fn expand_deriving_copy(
 }
 
 pub fn expand_deriving_const_param_ty(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -9,7 +9,7 @@ use rustc_span::Span;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_clone(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -10,7 +10,7 @@ use rustc_span::Span;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_eq(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs

@@ -8,7 +8,7 @@ use rustc_span::Span;
 use thin_vec::thin_vec;
 
 pub fn expand_deriving_ord(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs

@@ -9,7 +9,7 @@ use rustc_span::Span;
 use thin_vec::thin_vec;
 
 pub fn expand_deriving_partial_eq(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs

@@ -8,7 +8,7 @@ use rustc_span::Span;
 use thin_vec::thin_vec;
 
 pub fn expand_deriving_partial_ord(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -9,7 +9,7 @@ use rustc_span::Span;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_debug(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/decodable.rs

@@ -11,7 +11,7 @@ use rustc_span::Span;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_rustc_decodable(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -13,7 +13,7 @@ use smallvec::SmallVec;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_default(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &ast::MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/encodable.rs

@@ -95,7 +95,7 @@ use rustc_span::Span;
 use thin_vec::{thin_vec, ThinVec};
 
 pub fn expand_deriving_rustc_encodable(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/hash.rs

@@ -8,7 +8,7 @@ use rustc_span::Span;
 use thin_vec::thin_vec;
 
 pub fn expand_deriving_hash(
-    cx: &mut ExtCtxt<'_>,
+    cx: &ExtCtxt<'_>,
     span: Span,
     mitem: &MetaItem,
     item: &Annotatable,

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -40,7 +40,7 @@ pub mod partial_ord;
 pub mod generic;
 
 pub(crate) type BuiltinDeriveFn =
-    fn(&mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable), bool);
+    fn(&ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable), bool);
 
 pub(crate) struct BuiltinDerive(pub(crate) BuiltinDeriveFn);