workaround for allocations when broadcasting equations

src/equations/equations.jl

@@ -75,8 +75,14 @@ end
 
 @inline Base.ndims(::AbstractEquations{NDIMS}) where {NDIMS} = NDIMS
 
-# equations act like scalars in broadcasting
-Base.broadcastable(equations::AbstractEquations) = Ref(equations)
+# Equations act like scalars in broadcasting.
+# Using `Ref(equations)` would be more convenient in some circumstances.
+# However, this does not work with Julia v1.9.3 correctly due to a (performance)
+# bug in Julia, see
+# - https://github.com/trixi-framework/Trixi.jl/pull/1618
+# - https://github.com/JuliaLang/julia/issues/51118
+# Thus, we use the workaround below.
+Base.broadcastable(equations::AbstractEquations) = (equations,)
 
 """
     flux(u, orientation_or_normal, equations)