From e8265906a4be223442e068f14645b802c5f1b5bf Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Fri, 13 Sep 2024 12:57:05 +1200
Subject: [PATCH 1/2] Fix an illegal simplification in MA.operate!! for
 NonlinearExpr

---
 src/nlp_expr.jl       | 11 ++++++++---
 test/test_nlp_expr.jl |  9 +++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/nlp_expr.jl b/src/nlp_expr.jl
index 6393ea297e0..066610bb8ba 100644
--- a/src/nlp_expr.jl
+++ b/src/nlp_expr.jl
@@ -408,10 +408,15 @@ function _MA.operate!!(
     _throw_if_not_real(x)
     if any(isequal(_MA.Zero()), args)
         return x
-    elseif x.head == :+
-        push!(x.args, *(args...))
-        return x
     end
+    # It may seem like we should do this performance optimization, but it is NOT
+    # safe. See JuMP#3825. The issue is that even though we're calling operate!!
+    # `x` is not mutable, because it may, amoungst other things, be aliased in
+    # one of the args
+    # elseif x.head == :+
+    #     push!(x.args, *(args...))
+    #     return x
+    # end
     return +(x, *(args...))
 end
 
diff --git a/test/test_nlp_expr.jl b/test/test_nlp_expr.jl
index a92d624462e..3ef010f6e26 100644
--- a/test/test_nlp_expr.jl
+++ b/test/test_nlp_expr.jl
@@ -873,6 +873,15 @@ function test_ma_zero_in_operate!!()
     return
 end
 
+function test_ma_operate!!_nested_sum()
+    model = Model()
+    @variable(model, x)
+    y = NonlinearExpr(:+, Any[x])
+    z = MA.operate!!(MA.add_mul, y, y)
+    @test isequal_canonical(z, @force_nonlinear(+(+x, +x)))
+    return
+end
+
 function test_nonlinear_operator_inferred()
     model = Model()
     @variable(model, x)

From b2fbd671a588d70f6832ec548e5102b4a315154f Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Fri, 13 Sep 2024 12:58:53 +1200
Subject: [PATCH 2/2] Update

---
 test/test_nlp_expr.jl | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/test_nlp_expr.jl b/test/test_nlp_expr.jl
index 3ef010f6e26..afc555f7da4 100644
--- a/test/test_nlp_expr.jl
+++ b/test/test_nlp_expr.jl
@@ -878,6 +878,7 @@ function test_ma_operate!!_nested_sum()
     @variable(model, x)
     y = NonlinearExpr(:+, Any[x])
     z = MA.operate!!(MA.add_mul, y, y)
+    @test isequal_canonical(y, @force_nonlinear(+x))
     @test isequal_canonical(z, @force_nonlinear(+(+x, +x)))
     return
 end