#15114 force choice of coercion maps from UCF to CC, CIF, ...

Without this commit:

$ ./sage
sage: foo = E(17,2) + E(17,15)
sage: CC(foo)
1.47801783444132 - 2.43945488809238e-19*I
sage: CIF(foo)
1.478017834441319? + 0.?e-17*I

$ ./sage
sage: foo = E(17,2) + E(17,15)
sage: CIF(foo)
1.47801783444132?
sage: CC(foo)
1.47801783444132 - 2.43945488809238e-19*I

src/sage/rings/complex_mpfr.pyx

@@ -85,6 +85,7 @@ def late_import():
     global AlgebraicNumber_base
     global AlgebraicNumber
     global AlgebraicReal
+    global UniversalCyclotomicField
     global AA, QQbar, SR
     global CLF, RLF, CDF
     if NumberFieldElement_quadratic is None:
@@ -96,6 +97,7 @@ def late_import():
         AlgebraicNumber_base = sage.rings.qqbar.AlgebraicNumber_base
         AlgebraicNumber = sage.rings.qqbar.AlgebraicNumber
         AlgebraicReal = sage.rings.qqbar.AlgebraicReal
+        from sage.rings.universal_cyclotomic_field import UniversalCyclotomicField
         AA = sage.rings.qqbar.AA
         QQbar = sage.rings.qqbar.QQbar
         import sage.symbolic.ring
@@ -558,6 +560,13 @@ class ComplexField_class(ring.Field):
                 return None
         if S in [AA, QQbar, CLF, RLF]:
             return self._generic_coerce_map(S)
+        # Needed to discover the correct coerce map. Without this, the maps
+        # (direct or via QQbar, with slightly different behavior wrt imaginary
+        # parts of real elements) that get picked for conversion from UCF both
+        # to CC and to other types of complex fields depend in which order the
+        # coercions are discovered.
+        if isinstance(S, UniversalCyclotomicField):
+            return self._generic_coerce_map(S)
         return self._coerce_map_via([CLF], S)
 
     def _repr_(self):

src/sage/rings/universal_cyclotomic_field.py

@@ -256,7 +256,7 @@ class UCFtoQQbar(Morphism):
         -0.500000000000000? + 0.866025403784439?*I
 
         sage: CC(UCF.gen(7,2) + UCF.gen(7,6))
-        0.400968867902419 + 0.193096429713794*I
+        0.400968867902419 + 0.193096429713793*I
 
         sage: complex(E(7)+E(7,2))
         (0.40096886790241915+1.7567593946498534j)