Add deprecation comment in show.jl and deprecation item in NEWS.md

Author: davidavdav

NEWS.md

@@ -66,6 +66,8 @@ Deprecated or removed
 
   * `is` has been deprecated in favor of `===` (which used to be an alias for `is`) ([#17758]).
 
+  * infix operator `$` has been deprecated in favor of infix `⊻` or function `xor()` ([#18977]).
+
 Julia v0.5.0 Release Notes
 ==========================
 

base/show.jl

@@ -449,7 +449,7 @@ const uni_ops = Set{Symbol}([:(+), :(-), :(!), :(¬), :(~), :(<:), :(>:), :(√)
 const expr_infix_wide = Set{Symbol}([
     :(=), :(+=), :(-=), :(*=), :(/=), :(\=), :(^=), :(&=), :(|=), :(÷=), :(%=), :(>>>=), :(>>=), :(<<=),
     :(.=), :(.+=), :(.-=), :(.*=), :(./=), :(.\=), :(.^=), :(.&=), :(.|=), :(.÷=), :(.%=), :(.>>>=), :(.>>=), :(.<<=),
-    :(&&), :(||), :(<:), :(=>), :($=), :(⊻=)])
+    :(&&), :(||), :(<:), :(=>), :($=), :(⊻=)]) # `$=` should be removed after deprecation is removed, issue #18977
 const expr_infix = Set{Symbol}([:(:), :(->), Symbol("::")])
 const expr_infix_any = union(expr_infix, expr_infix_wide)
 const all_ops = union(quoted_syms, uni_ops, expr_infix_any)