Restrict &, | mr_empty fallbacks

Author: TotalVerb

base/process.jl

@@ -230,8 +230,6 @@ setenv(cmd::Cmd; dir="") = Cmd(cmd; dir=dir)
 (&)(left::AbstractCmd, right::AbstractCmd) = AndCmds(left, right)
 redir_out(src::AbstractCmd, dest::AbstractCmd) = OrCmds(src, dest)
 redir_err(src::AbstractCmd, dest::AbstractCmd) = ErrOrCmds(src, dest)
-Base.mr_empty(f, op::typeof(&), T::Type{<:Base.AbstractCmd}) =
-    throw(ArgumentError("reducing over an empty collection of type $T with operator & is not allowed"))
 
 # Stream Redirects
 redir_out(dest::Redirectable, src::AbstractCmd) = CmdRedirect(src, dest, STDIN_NO)

base/reduce.jl

@@ -239,8 +239,8 @@ mr_empty(::typeof(abs), op::typeof(scalarmax), T) = abs(zero(T))
 mr_empty(::typeof(abs2), op::typeof(scalarmax), T) = abs2(zero(T))
 mr_empty(::typeof(abs), op::typeof(max), T) = mr_empty(abs, scalarmax, T)
 mr_empty(::typeof(abs2), op::typeof(max), T) = mr_empty(abs2, scalarmax, T)
-mr_empty(f, op::typeof(&), T) = true
-mr_empty(f, op::typeof(|), T) = false
+mr_empty(::typeof(identity), op::typeof(&), ::Type{Bool}) = true
+mr_empty(::typeof(identity), op::typeof(|), ::Type{Bool}) = false
 
 # Allow mr_empty to “see through” promote_sys_size
 let ComposedFunction = typename(typeof(identity ∘ identity)).wrapper

test/reduce.jl

@@ -48,8 +48,8 @@
 @test mapreduce(abs2, +, Float64[]) === 0.0
 @test mapreduce(abs2, Base.scalarmax, Float64[]) === 0.0
 @test mapreduce(abs, max, Float64[]) === 0.0
-@test mapreduce(abs2, &, Float64[]) === true
-@test mapreduce(abs2, |, Float64[]) === false
+@test_throws ArgumentError mapreduce(abs2, &, Float64[])
+@test_throws ArgumentError mapreduce(abs2, |, Float64[])
 
 # mapreduce() type stability
 @test typeof(mapreduce(*, +, Int8[10])) ===
@@ -397,3 +397,7 @@ test18695(r) = sum( t^2 for t in r )
 
 # issue #21107
 @test foldr(-,2:2) == 2
+
+# test neutral element not picked incorrectly for &, |
+@test @inferred(foldl(&, Int[1])) === 1
+@test_throws ArgumentError foldl(&, Int[])