bug loading MPL style from the configuration (#11750)

* config path fixing

* reno

* add test

* temp file creation

* Avoid using more internal details in style test

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
(cherry picked from commit 19c15b7)

# Conflicts:
#	qiskit/visualization/circuit/qcstyle.py
#	test/python/visualization/test_circuit_drawer.py

qiskit/visualization/circuit/qcstyle.py

@@ -418,3 +418,75 @@ def set_style(current_style, new_style):
             UserWarning,
             2,
         )
+<<<<<<< HEAD
+=======
+        style_name = "default"
+
+    if style_name in ["iqp", "default"]:
+        current_style = DefaultStyle().style
+    else:
+        # Search for file in 'styles' dir, then config_path, and finally the current directory
+        style_name = style_name + ".json"
+        style_paths = []
+
+        default_path = Path(__file__).parent / "styles" / style_name
+        style_paths.append(default_path)
+
+        # check configured paths, if there are any
+        if config:
+            config_path = config.get("circuit_mpl_style_path", "")
+            if config_path:
+                for path in config_path:
+                    style_paths.append(Path(path) / style_name)
+
+        # check current directory
+        cwd_path = Path("") / style_name
+        style_paths.append(cwd_path)
+
+        for path in style_paths:
+            # expand ~ to the user directory and check if the file exists
+            exp_user = path.expanduser()
+            if os.path.isfile(exp_user):
+                try:
+                    with open(exp_user) as infile:
+                        json_style = json.load(infile)
+
+                    current_style = StyleDict(json_style)
+                    break
+                except json.JSONDecodeError as err:
+                    warn(
+                        f"Could not decode JSON in file '{path}': {str(err)}. "
+                        "Will use default style.",
+                        UserWarning,
+                        2,
+                    )
+                    break
+                except (OSError, FileNotFoundError):
+                    warn(
+                        f"Error loading JSON file '{path}'. Will use default style.",
+                        UserWarning,
+                        2,
+                    )
+                    break
+        else:
+            warn(
+                f"Style JSON file '{style_name}' not found in any of these locations: "
+                f"{', '.join(map(str, style_paths))}. "
+                "Will use default style.",
+                UserWarning,
+                2,
+            )
+            current_style = DefaultStyle().style
+
+    # if the style is a dictionary, update the defaults with the new values
+    # this _needs_ to happen after loading by name to cover cases like
+    #   style = {"name": "bw", "edgecolor": "#FF0000"}
+    if isinstance(style, dict):
+        current_style.update(style)
+
+    # this is the default font ratio
+    # if the font- or subfont-sizes are changed, the new size is based on this ratio
+    def_font_ratio = 13 / 8
+
+    return current_style, def_font_ratio
+>>>>>>> 19c15b749 (bug loading MPL style from the configuration (#11750))

qiskit/visualization/circuit/styles/__init__.py

@@ -0,0 +1,13 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2014.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Empty init for data directory."""

releasenotes/notes/fix_11536-c87d192a133b3dc3.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    A bug when loading MPL style from the configuration was fixed.

test/python/visualization/test_circuit_drawer.py

@@ -12,15 +12,22 @@
 
 # pylint: disable=missing-docstring
 
-import unittest
 import os
+<<<<<<< HEAD
+=======
+import pathlib
+import shutil
+import tempfile
+import unittest
+import warnings
+>>>>>>> 19c15b749 (bug loading MPL style from the configuration (#11750))
 from unittest.mock import patch
 
 from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
 from qiskit.test import QiskitTestCase
 from qiskit.utils import optionals
 from qiskit import visualization
-from qiskit.visualization.circuit import text
+from qiskit.visualization.circuit import text, styles
 from qiskit.visualization.exceptions import VisualizationError
 
 if optionals.HAS_MATPLOTLIB:
@@ -49,6 +56,38 @@ def test_default_output(self):
             out = visualization.circuit_drawer(circuit)
             self.assertIsInstance(out, text.TextDrawing)
 
+    @unittest.skipUnless(optionals.HAS_MATPLOTLIB, "Skipped because matplotlib is not available")
+    def test_mpl_config_with_path(self):
+        # It's too easy to get too nested in a test with many context managers.
+        tempdir = tempfile.TemporaryDirectory()  # pylint: disable=consider-using-with
+        self.addCleanup(tempdir.cleanup)
+
+        clifford_style = pathlib.Path(styles.__file__).parent / "clifford.json"
+        shutil.copyfile(clifford_style, pathlib.Path(tempdir.name) / "my_clifford.json")
+
+        circuit = QuantumCircuit(1)
+        circuit.h(0)
+
+        def config(style_name):
+            return {
+                "circuit_drawer": "mpl",
+                "circuit_mpl_style": style_name,
+                "circuit_mpl_style_path": [tempdir.name],
+            }
+
+        with warnings.catch_warnings():
+            warnings.filterwarnings("error", message="Style JSON file.*not found")
+
+            # Test that a non-standard style can be loaded by name.
+            with patch("qiskit.user_config.get_config", return_value=config("my_clifford")):
+                self.assertIsInstance(visualization.circuit_drawer(circuit), figure.Figure)
+
+            # Test that a non-existent style issues a warning, but still draws something.
+            with patch("qiskit.user_config.get_config", return_value=config("NONEXISTENT")):
+                with self.assertWarnsRegex(UserWarning, "Style JSON file.*not found"):
+                    fig = visualization.circuit_drawer(circuit)
+                self.assertIsInstance(fig, figure.Figure)
+
     @unittest.skipUnless(optionals.HAS_MATPLOTLIB, "Skipped because matplotlib is not available")
     def test_user_config_default_output(self):
         with patch("qiskit.user_config.get_config", return_value={"circuit_drawer": "mpl"}):