inheritance of contradictory parametric type constraints

[WschW]

Abstract and concrete parametric types can inherit from other parametric types with contradictory type constraints for example:

julia> abstract type A{T<:Int} end

julia> abstract type B{T<:Array} <: A{T} end

julia> struct C{T} <: B{T}
                f::T
              end

None of these types can ever be used

julia> B{Array}
ERROR: TypeError: in A, in T, expected T<:Int64, got Type{Array}
Stacktrace:
 [1] top-level scope at none:0

julia> B{Int}
ERROR: TypeError: in B, in T, expected T<:Array, got Type{Int64}
Stacktrace:
 [1] top-level scope at none:0

julia> C(3)
ERROR: TypeError: in B, in T, expected T<:Array, got Type{Int64}
Stacktrace:
 [1] C(::Int64) at ./REPL[3]:2
 [2] top-level scope at none:0

julia> c([3])
ERROR: UndefVarError: c not defined
Stacktrace:
 [1] top-level scope at none:0

julia> versioninfo()
Julia Version 1.0.1
Commit 0d713926f8 (2018-09-29 19:05 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, haswell)

[JeffBezanson]

Mostly a duplicate of #9441. (#24179 also slightly related)

[JeffBezanson]

Closing as duplicate of #9441.