FIX: resolve an issue where no ticks would be drawn for a colorbar with SymLogNorm and ranging exactly from 0 to linthresh

Co-authored-by: Ruth Comer <[email protected]>

Author: neutrinoceros

lib/matplotlib/tests/test_ticker.py

@@ -506,6 +506,19 @@ def test_set_params(self):
         assert sym._subs == [2.0]
         assert sym.numticks == 8
 
+    @pytest.mark.parametrize(
+            'vmin, vmax, expected',
+            [
+                (0, 1, [0, 1]),
+                (-1, 1, [-1, 0, 1]),
+            ],
+    )
+    def test_values(self, vmin, vmax, expected):
+        # https://github.com/matplotlib/matplotlib/issues/25945
+        sym = mticker.SymmetricalLogLocator(base=10, linthresh=1)
+        ticks = sym.tick_values(vmin=vmin, vmax=vmax)
+        assert_array_equal(ticks, expected)
+
 
 class TestAsinhLocator:
     def test_init(self):

lib/matplotlib/ticker.py

@@ -2496,11 +2496,11 @@ def tick_values(self, vmin, vmax):
         # We could also add ticks at t, but that seems to usually be
         # uninteresting.
         #
-        # "simple" mode is when the range falls entirely within (-t,
-        # t) -- it should just display (vmin, 0, vmax)
-        if -linthresh < vmin < vmax < linthresh:
+        # "simple" mode is when the range falls entirely within [-t, t]
+        #  -- it should just display (vmin, 0, vmax)
+        if -linthresh <= vmin < vmax <= linthresh:
             # only the linear range is present
-            return [vmin, vmax]
+            return sorted({vmin, 0, vmax})
 
         # Lower log range is present
         has_a = (vmin < -linthresh)