Deprecate isimag.

Author: Sacha0

base/complex.jl

@@ -90,12 +90,6 @@ false
 """
 isreal(x::Real) = true
 isreal(z::Complex) = iszero(imag(z))
-"""
-    isimag(z) -> Bool
-
-Test whether `z` is purely imaginary, i.e. has a real part equal to 0.
-"""
-isimag(z::Number) = iszero(real(z))
 isinteger(z::Complex) = isreal(z) & isinteger(real(z))
 isfinite(z::Complex) = isfinite(real(z)) & isfinite(imag(z))
 isnan(z::Complex) = isnan(real(z)) | isnan(imag(z))

base/deprecated.jl

@@ -1276,6 +1276,9 @@ eval(SparseArrays, :(broadcast_zpreserving!(f, C::SparseMatrixCSC, A::Union{Arra
 @deprecate getindex(t::Tuple, r::AbstractArray)       getindex(t, vec(r))
 @deprecate getindex(t::Tuple, b::AbstractArray{Bool}) getindex(t, vec(b))
 
+# Deprecate isimag (#19947).
+@deprecate isimag(z::Number) Base.iszero(real(z))
+
 @deprecate airy(z::Number) airyai(z)
 @deprecate airyx(z::Number) airyaix(z)
 @deprecate airyprime(z::Number) airyaiprime(z)

test/complex.jl

@@ -147,9 +147,9 @@ end
     end
 end
 
-@testset "isimag and isinf" begin
-    @test isimag(complex(0.0,1.0))
-    @test !isimag(complex(1.0,1.0))
+@testset "isinf" begin
+    @test Base.iszero(real(complex(0.0,1.0))) # isimag deprecated
+    @test !Base.iszero(real(complex(1.0,1.0))) # isimag deprecated
     @test isinf(complex(Inf,0))
     @test isinf(complex(-Inf,0))
     @test isinf(complex(0,Inf))