From 9145948118c9ed41a99115907f7cc3f74235dbc6 Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Tue, 4 Feb 2025 08:22:27 +1300
Subject: [PATCH] Fix bug copying expressions that do not contain variables

---
 src/copy.jl        |  5 +++++
 test/test_model.jl | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/copy.jl b/src/copy.jl
index ae8c9c8aa15..7ffa2c7b09b 100644
--- a/src/copy.jl
+++ b/src/copy.jl
@@ -45,6 +45,11 @@ end
 
 const ReferenceMap = GenericReferenceMap{Float64}
 
+# Some fallbacks for Base types that we should pass through un-changed
+Base.getindex(::GenericReferenceMap, x::Number) = x
+Base.getindex(::GenericReferenceMap, x::AbstractString) = x
+Base.getindex(::GenericReferenceMap, x::Symbol) = x
+
 function Base.getindex(map::GenericReferenceMap, vref::GenericVariableRef)
     return GenericVariableRef(map.model, map.index_map[index(vref)])
 end
diff --git a/test/test_model.jl b/test/test_model.jl
index 74e5d7046cd..b09956248ae 100644
--- a/test/test_model.jl
+++ b/test/test_model.jl
@@ -1465,4 +1465,18 @@ function test_solver_name_error()
     return
 end
 
+function test_copy_base_types()
+    model = Model()
+    @expression(model, a, 1.0)
+    @expression(model, b, "Bb")
+    @expression(model, c, :c)
+    @expression(model, d, BigInt(1) + BigInt(2) * im)
+    new_model = copy(model)
+    @test new_model[:a] === 1.0
+    @test new_model[:b] == "Bb"
+    @test new_model[:c] == :c
+    @test new_model[:d] == BigInt(1) + BigInt(2) * im
+    return
+end
+
 end  # module TestModels