Remove at-compat for type aliases

Was added in #326, now obsolete as no longer required on minimum
supported Julia version 0.6.

README.md

@@ -68,9 +68,6 @@ Currently, the `@compat` macro supports the following syntaxes:
   to declare abstract and primitive types. [#20418]
   This only works when `@compat` is applied directly on the declaration.
 
-* `@compat A{T} = B{T}` or `@compat const A{T} = B{T}` to declare type alias with free
-  parameters. [#20500]. Use `const A = B{T}` or `const A = B` for type alias without free parameters (i.e. no type parameter on the left hand side).
-
 * `@compat Base.IndexStyle(::Type{<:MyArray}) = IndexLinear()` and `@compat Base.IndexStyle(::Type{<:MyArray}) = IndexCartesian()` to define traits for abstract arrays, replacing the former `Base.linearindexing{T<:MyArray}(::Type{T}) = Base.LinearFast()` and `Base.linearindexing{T<:MyArray}(::Type{T}) = Base.LinearSlow()`, respectively.
 
 * `Compat.collect(A)` returns an `Array`, no matter what indices the array `A` has. [#21257]
@@ -550,7 +547,6 @@ includes this fix. Find the minimum version from there.
 [#20407]: https://github.com/JuliaLang/julia/issues/20407
 [#20414]: https://github.com/JuliaLang/julia/issues/20414
 [#20418]: https://github.com/JuliaLang/julia/issues/20418
-[#20500]: https://github.com/JuliaLang/julia/issues/20500
 [#20974]: https://github.com/JuliaLang/julia/issues/20974
 [#21197]: https://github.com/JuliaLang/julia/issues/21197
 [#21257]: https://github.com/JuliaLang/julia/issues/21257

src/compatmacro.jl

@@ -15,16 +15,6 @@ is_index_style(arg) = false
 
 istopsymbol(ex, mod, sym) = ex in (sym, Expr(:(.), mod, Expr(:quote, sym)))
 
-if VERSION < v"0.6.0-dev.2782"
-    function new_style_typealias(ex::ANY)
-        isexpr(ex, :(=)) || return false
-        ex = ex::Expr
-        return length(ex.args) == 2 && isexpr(ex.args[1], :curly)
-    end
-else
-    new_style_typealias(ex) = false
-end
-
 if !isdefined(Base, :UndefKeywordError)
     struct UndefKeywordError <: Exception
         kw
@@ -62,11 +52,6 @@ function _compat(ex::Expr)
     elseif ex.head === :quote && isa(ex.args[1], Symbol)
         # Passthrough
         return ex
-    elseif new_style_typealias(ex)
-        ex.head = :typealias
-    elseif ex.head === :const && length(ex.args) == 1 && new_style_typealias(ex.args[1])
-        ex = ex.args[1]::Expr
-        ex.head = :typealias
     end
     if VERSION < v"0.6.0-dev.2840"
         if ex.head == :(=) && isa(ex.args[1], Expr) && ex.args[1].head == :call

test/runtests.jl

@@ -476,14 +476,6 @@ end
 @test isbitstype(Primitive20418{Int})
 @test sizeof(Primitive20418{Int}) == 2
 
-# PR #20500
-@compat A20500{T<:Integer} = Array{T,20500}
-@compat const A20500_2{T<:Union{Int,Float32}} = Pair{T,T}
-f20500() = A20500
-f20500_2() = A20500_2
-@inferred f20500()
-@inferred f20500_2()
-
 module CompatArray
     using Compat
     const struct_sym = VERSION < v"0.7.0-DEV.1263" ? :type : :struct