Add Constant handler for ufl2unicode now it's a DAGTraverser (#5058)

* Add Constant handler to ufl2unicode
* Make ufl2unicode tests for Constant stronger

Author: connorjward

firedrake/constant.py

@@ -13,8 +13,7 @@
 from ufl.core.ufl_type import UFLType
 from ufl.corealg.multifunction import MultiFunction
 from ufl.formatting.ufl2unicode import (
-    Expression2UnicodeHandler, UC, subscript_number, PrecedenceRules,
-    colorama,
+    Expression2UnicodeHandler, UC, subscript_number, colorama,
 )
 from functools import cached_property
 from ufl.utils.counted import Counted
@@ -192,7 +191,7 @@ def _unicode_format_firedrake_constant(self, o):
 
 
 # This monkey patches ufl2unicode support for Firedrake constants
-Expression2UnicodeHandler.firedrake_constant = _unicode_format_firedrake_constant
+Expression2UnicodeHandler.process.register(Constant, _unicode_format_firedrake_constant)
 
 # This is internally done in UFL by the ufl_type decorator, but we cannot
 # do the same here, because we want to use the class name Constant
@@ -209,4 +208,3 @@ def _unicode_format_firedrake_constant(self, o):
 
 # These caches need rebuilding for the new type to be registered
 MultiFunction._handlers_cache = {}
-ufl.formatting.ufl2unicode._precrules = PrecedenceRules()

tests/firedrake/regression/test_constant.py

@@ -277,17 +277,17 @@ def test_derivative_wrt_constant():
 
 def test_constant_ufl2unicode():
     mesh = UnitIntervalMesh(1)
-    a = Constant(1.0, name="a")
-    b = Constant(2.0, name="b")
+    a = Constant(1.0, name="a", count=0)
+    b = Constant(2.0, name="b", count=1)
     F = a * a * b * b * dx(mesh)
-    _ = ufl2unicode(F)
+    assert ufl2unicode(F) == "∫[rest of domain] ((C₀ C₀) C₁) C₁ 𝐝𝐱"
 
     dFda = derivative(F, u=a)
     dFdb = derivative(F, u=b)
-    _ = ufl2unicode(dFda)
-    _ = ufl2unicode(dFdb)
+    assert ufl2unicode(dFda) == "∫[rest of domain] ((v C₀ + v C₀) C₁) C₁ 𝐝𝐱"
+    assert ufl2unicode(dFdb) == "∫[rest of domain] v (C₀ C₀) C₁ + (v C₀ C₀) C₁ 𝐝𝐱"
 
     dFda_du = derivative(F, u=a, du=IntValue(1))
     dFdb_du = derivative(F, u=b, du=IntValue(1))
-    _ = ufl2unicode(dFda_du)
-    _ = ufl2unicode(dFdb_du)
+    assert ufl2unicode(dFda_du) == "∫[rest of domain] ((C₀ + C₀) C₁) C₁ 𝐝𝐱"
+    assert ufl2unicode(dFdb_du) == "∫[rest of domain] (C₀ C₀) C₁ + (C₀ C₀) C₁ 𝐝𝐱"