From b8acca9c66096574ede0edb543f980c07aaecc87 Mon Sep 17 00:00:00 2001
From: Oscar Dowson <o.dowson@gmail.com>
Date: Wed, 10 Jun 2026 01:20:22 +1200
Subject: [PATCH] [Utilities] fix use of recursion in
 canonicalize!(::ScalarNonlinearFunction)

---
 src/Utilities/functions.jl       | 14 +++++++++++---
 test/Utilities/test_functions.jl | 13 +++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/Utilities/functions.jl b/src/Utilities/functions.jl
index e88ae35416..a512d380db 100644
--- a/src/Utilities/functions.jl
+++ b/src/Utilities/functions.jl
@@ -1072,9 +1072,17 @@ function canonicalize!(
 end
 
 function canonicalize!(f::MOI.ScalarNonlinearFunction)
-    for (i, arg) in enumerate(f.args)
-        if !is_canonical(arg)
-            f.args[i] = canonicalize!(arg)
+    # Don't use recursion here. This gets called for all scalar nonlinear
+    # constraints.
+    stack = MOI.ScalarNonlinearFunction[f]
+    while !isempty(stack)
+        g = pop!(stack)
+        for (i, arg) in enumerate(g.args)
+            if arg isa MOI.ScalarNonlinearFunction
+                push!(stack, arg)
+            elseif !is_canonical(arg)
+                g.args[i] = canonicalize!(arg)
+            end
         end
     end
     return f
diff --git a/test/Utilities/test_functions.jl b/test/Utilities/test_functions.jl
index 1d59ee3773..836ad3dffa 100644
--- a/test/Utilities/test_functions.jl
+++ b/test/Utilities/test_functions.jl
@@ -2044,6 +2044,19 @@ function test_ScalarNonlinearFunction_is_canonical()
         f = MOI.ScalarNonlinearFunction(:sin, Any[f])
     end
     @test MOI.Utilities.is_canonical(f)
+    @test MOI.Utilities.canonicalize!(f) isa MOI.ScalarNonlinearFunction
+    g = MOI.ScalarNonlinearFunction(:^, Any[1.0 * x + 1.0 * x, 2])
+    for _ in 1:100_000
+        g = MOI.ScalarNonlinearFunction(:sin, Any[g])
+    end
+    @test !MOI.Utilities.is_canonical(g)
+    MOI.Utilities.canonicalize!(g)
+    h = MOI.ScalarNonlinearFunction(:^, Any[2.0 * x, 2])
+    for _ in 1:100_000
+        h = MOI.ScalarNonlinearFunction(:sin, Any[h])
+    end
+    @test MOI.Utilities.is_canonical(h)
+    @test isapprox(g, h)
     return
 end