Update

src/macros.jl

@@ -474,3 +474,30 @@ for file in readdir(joinpath(@__DIR__, "macros"))
         include(joinpath(@__DIR__, "macros", file))
     end
 end
+
+# These methods must come after the macros are included, because they use both
+# `@variable` and `@constraint`.
+
+function _build_subexpression(
+    ::Function,
+    model::AbstractModel,
+    expr::AbstractJuMPScalar,
+    name::String,
+)
+    y = @variable(model)
+    set_name(y, name)
+    @constraint(model, y == expr)
+    return y
+end
+
+function _build_subexpression(
+    ::Function,
+    model::AbstractModel,
+    expr::Array{<:AbstractJuMPScalar},
+    name::String,
+)
+    y = [@variable(model) for _ in expr]
+    set_name.(y, name)
+    @constraint(model, y .== expr)
+    return y
+end

src/macros/@expression.jl

@@ -103,30 +103,6 @@ macro expression(input_args...)
     )
 end
 
-function _build_subexpression(
-    ::Function,
-    model::AbstractModel,
-    expr::AbstractJuMPScalar,
-    name::String,
-)
-    y = @variable(model)
-    set_name(y, name)
-    @constraint(model, y == expr)
-    return y
-end
-
-function _build_subexpression(
-    ::Function,
-    model::AbstractModel,
-    expr::Array{<:AbstractJuMPScalar},
-    name::String,
-)
-    y = [@variable(model) for _ in expr]
-    set_name.(y, name)
-    @constraint(model, y .== expr)
-    return y
-end
-
 function _build_subexpression(
     error_fn::Function,
     ::AbstractModel,