Fix complex variables of custom coefficient type (#3691)

src/variables.jl

@@ -2104,10 +2104,10 @@ function add_variable(
     real_part = add_variable(model, _real(var), _real(name))
     imag_part = add_variable(model, _imag(var), _imag(name))
     # Efficiently build `real_part + imag_part * im`
-    return GenericAffExpr{ComplexF64,GenericVariableRef{T}}(
-        zero(ComplexF64),
-        real_part => one(ComplexF64),
-        imag_part => convert(ComplexF64, im),
+    return GenericAffExpr{Complex{T},GenericVariableRef{T}}(
+        zero(Complex{T}),
+        real_part => one(Complex{T}),
+        imag_part => convert(Complex{T}, im),
     )
 end
 

test/test_complex.jl

@@ -292,4 +292,22 @@ function test_HermitianPSDCone_general_matrix_error()
     return
 end
 
+function test_complex_generic_number_type()
+    for T in (Float32, Float64, Rational{BigInt}, BigFloat)
+        model = GenericModel{T}()
+        @variable(model, x in ComplexPlane())
+        @test x isa GenericAffExpr{Complex{T},GenericVariableRef{T}}
+    end
+    return
 end
+
+function test_hermitian_generic_number_type()
+    for T in (Float32, Float64, Rational{BigInt}, BigFloat)
+        model = GenericModel{T}()
+        @variable(model, x[1:2, 1:2], Hermitian)
+        @test x[1, 1] isa GenericAffExpr{Complex{T},GenericVariableRef{T}}
+    end
+    return
+end
+
+end  # TestComplexNumberSupport