Change style of DAG generated in dag_drawer()

MANIFEST.in

@@ -3,6 +3,7 @@ include requirements.txt
 recursive-include qiskit/qasm/libs *.inc
 include qiskit/VERSION.txt
 include qiskit/visualization/circuit/styles/*.json
+include qiskit/visualization/dag/styles/*.json
 recursive-include qiskit/providers/fake_provider/backends_v1 *.json
 
 # Include the tests files.

qiskit/visualization/dag/__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."""

qiskit/visualization/dag/dagstyle.py

@@ -0,0 +1,211 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2019.
+#
+# 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.
+
+"""Matplotlib circuit visualization style."""
+
+from __future__ import annotations
+
+import json
+import os
+from typing import Any
+from pathlib import Path
+from warnings import warn
+from qiskit.visualization import exceptions
+
+
+class StyleDict(dict):
+    """A dictionary for graphviz styles.
+
+    Defines additional abbreviations for key accesses, such as allowing
+    ``"ec"`` instead of writing ``"edgecolor"``.
+    """
+
+    VALID_FIELDS = {
+        "name",
+        "fontsize",
+        "bgcolor",
+        "dpi",
+        "pad",
+        "nodecolor",
+        "inputnodecolor",
+        "inputnodefontcolor",
+        "outputnodecolor",
+        "outputnodefontcolor",
+        "opnodecolor",
+        "opnodefontcolor",
+        "edgecolor",
+        "qubitedgecolor",
+        "clbitedgecolor",
+    }
+
+    ABBREVIATIONS = {
+        "nc": "nodecolor",
+        "ic": "inputnodecolor",
+        "if": "inputnodefontcolor",
+        "oc": "outputnodecolor",
+        "of": "outputnodefontcolor",
+        "opc": "opnodecolor",
+        "opf": "opnodefontcolor",
+        "ec": "edgecolor",
+        "qec": "qubitedgecolor",
+        "clc": "clbitedgecolor",
+    }
+
+    def __setitem__(self, key: Any, value: Any) -> None:
+        # allow using field abbreviations
+        if key in self.ABBREVIATIONS:
+            key = self.ABBREVIATIONS[key]
+
+        if key not in self.VALID_FIELDS:
+            warn(
+                f"style option ({key}) is not supported",
+                UserWarning,
+                2,
+            )
+        return super().__setitem__(key, value)
+
+    def __getitem__(self, key: Any) -> Any:
+        # allow using field abbreviations
+        if key in self.ABBREVIATIONS:
+            key = self.ABBREVIATIONS[key]
+
+        return super().__getitem__(key)
+
+    def update(self, other):
+        super().update((key, value) for key, value in other.items())
+
+
+class DefaultStyle:
+    """Creates a Default Style dictionary
+
+    The style dict contains numerous options that define the style of the
+    output circuit visualization. The style dict is used by the `mpl` or
+    `latex` output. The options available in the style dict are defined below:
+
+    Attributes:
+        name (str): The name of the style.
+        fontsize (str): The font size to use for text.
+        bgcolor (str): The color name to use for the background ('red', 'green', etc.).
+        nodecolor (str): The color to use for all nodes.
+        dpi (int): The DPI to use for the output image.
+        pad (int): A number to adjust padding around output
+            graph.
+        inputnodecolor (str): The color to use for incoming wire nodes. Overrides
+            nodecolor for those nodes.
+        inputnodefontcolor (str): The font color to use for incoming wire nodes.
+            Overrides nodecolor for those nodes.
+        outputnodecolor (str): The color to use for output wire nodes. Overrides
+            nodecolor for those nodes.
+        outputnodefontcolor (str): The font color to use for output wire nodes.
+            Overrides nodecolor for those nodes.
+        opnodecolor (str): The color to use for Instruction nodes. Overrides
+            nodecolor for those nodes.
+        opnodefontcolor (str): The font color to use for Instruction nodes.
+            Overrides nodecolor for those nodes.
+
+        qubitedgecolor (str): The edge color for qubits. Overrides edgecolor for these edges.
+        clbitedgecolor (str): The edge color for clbits. Overrides edgecolor for these edges.
+    """
+
+    def __init__(self):
+        default_style_dict = "color.json"
+        path = Path(__file__).parent / "styles" / default_style_dict
+
+        with open(path, "r") as infile:
+            default_style = json.load(infile)
+
+        # set shortcuts, such as "ec" for "edgecolor"
+        self.style = StyleDict(**default_style)
+
+
+def load_style(style: dict | str = "color") -> StyleDict:
+    """Utility function to load style from json files.
+
+    Args:
+        style: Depending on the type, this acts differently:
+
+            * If a string, it can specify a supported style name (such
+              as "iqp" or "clifford"). It can also specify the name of
+              a custom color scheme stored as JSON file. This JSON file
+              _must_ specify a complete set of colors.
+            * If a dictionary, it may specify the style name via a
+              ``{"name": "<desired style>"}`` entry. If this is not given,
+              the default style will be used. The remaining entries in the
+              dictionary can be used to override certain specs.
+              E.g. ``{"name": "iqp", "ec": "#FF0000"}`` will use the ``"iqp"``
+              color scheme but set the edgecolor to red.
+
+    Returns:
+        A tuple containing the style as dictionary and the default font ratio.
+    """
+
+    # determine the style name which could also be inside a dictionary, like
+    # style={"name": "clifford", <other settings...>}
+    if isinstance(style, dict):
+        style_name = style.get("name", "color")
+    elif isinstance(style, str):
+        if style.endswith(".json"):
+            style_name = style[:-5]
+        else:
+            style_name = style
+    else:
+        raise exceptions.VisualizationError("Invalid style {style}")
+
+    if style_name in ["color"]:
+        current_style = DefaultStyle().style
+    else:
+        # Search for file in 'styles' dir, and then the current directory
+        style_name = style_name + ".json"
+        style_paths = []
+
+        default_path = Path(__file__).parent / "styles" / style_name
+        style_paths.append(default_path)
+
+        # 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:
+            raise exceptions.VisualizationError(f"Invalid style {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)
+
+    return current_style

qiskit/visualization/dag/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."""

qiskit/visualization/dag/styles/color.json

@@ -0,0 +1,6 @@
+{
+  "name": "color",
+  "inputnodecolor": "green",
+  "outputnodecolor": "red",
+  "opnodecolor": "lightblue"
+}

qiskit/visualization/dag/styles/plain.json

@@ -0,0 +1,6 @@
+{
+  "name": "plain",
+  "inputnodecolor": "white",
+  "outputnodecolor": "white",
+  "opnodecolor": "white"
+}