Use sphinx.ext.linkcode for more precise source code links (#2101)

* switched links to using sphinx.ext.linkcode

* added release note

* added check for qiskit methods

* remove whitespace

* removed regex subsitution

Co-authored-by: Eric Arellano <14852634+Eric-Arellano@users.noreply.github.com>

* Update tox.ini

Co-authored-by: Eric Arellano <14852634+Eric-Arellano@users.noreply.github.com>

* made updates following Eric's review

* made final line more readable

* cast filename to str

* re-added regex sub

---------

Co-authored-by: Eric Arellano <14852634+Eric-Arellano@users.noreply.github.com>

docs/conf.py

@@ -31,8 +31,12 @@
 Sphinx documentation builder
 """
 
-import os
 import datetime
+import importlib
+import inspect
+import os
+import re
+from pathlib import Path
 # Set env flag so that we can doc functions that may otherwise not be loaded
 # see for example interactive visualizations in qiskit.visualization.
 os.environ['QISKIT_DOCS'] = 'TRUE'
@@ -64,7 +68,7 @@ extensions = [
     'sphinx.ext.autodoc',
     'sphinx.ext.autosummary',
     'sphinx.ext.mathjax',
-    'sphinx.ext.viewcode',
+    "sphinx.ext.linkcode",
     'sphinx.ext.extlinks',
     'jupyter_sphinx',
     'reno.sphinxext',
@@ -146,3 +150,82 @@ intersphinx_mapping = {
     "matplotlib": ("https://matplotlib.org/stable/", None),
     "qiskit": ("https://docs.quantum.ibm.com/api/qiskit/", None),
 }
+
+
+# ----------------------------------------------------------------------------------
+# Source code links
+# ----------------------------------------------------------------------------------
+
+def determine_github_branch() -> str:
+    """Determine the GitHub branch name to use for source code links.
+
+    We need to decide whether to use `stable/<version>` vs. `main` for dev builds.
+    Refer to https://docs.github.com/en/actions/learn-github-actions/variables
+    for how we determine this with GitHub Actions.
+    """
+    # If CI env vars not set, default to `main`. This is relevant for local builds.
+    if "GITHUB_REF_NAME" not in os.environ:
+        return "main"
+
+    # PR workflows set the branch they're merging into.
+    if base_ref := os.environ.get("GITHUB_BASE_REF"):
+        return base_ref
+
+    ref_name = os.environ["GITHUB_REF_NAME"]
+
+    # Check if the ref_name is a tag like `1.0.0` or `1.0.0rc1`. If so, we need
+    # to transform it to a Git branch like `stable/1.0`.
+    version_without_patch = re.match(r"(\d+\.\d+)", ref_name)
+    return (
+        f"stable/{version_without_patch.group()}"
+        if version_without_patch
+        else ref_name
+    )
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+GITHUB_BRANCH = determine_github_branch()
+
+
+def linkcode_resolve(domain, info):
+    if domain != "py":
+        return None
+
+    module_name = info["module"]
+    if "qiskit_aer" not in module_name:
+        return None
+
+    try:
+        module = importlib.import_module(module_name)
+    except ModuleNotFoundError:
+        return None
+
+    obj = module
+    for part in info["fullname"].split("."):
+        try:
+            obj = getattr(obj, part)
+        except AttributeError:
+            return None
+
+    try:
+        full_file_name = inspect.getsourcefile(obj)
+    except TypeError:
+        return None
+    if full_file_name is None:
+        return None
+    try:
+        relative_file_name = Path(full_file_name).resolve().relative_to(REPO_ROOT)
+        file_name = re.sub(r"\.tox\/.+\/site-packages\/", "", str(relative_file_name))
+    except ValueError:
+        return None
+
+    try:
+        source, lineno = inspect.getsourcelines(obj)
+    except (OSError, TypeError):
+        linespec = ""
+    else:
+        ending_lineno = lineno + len(source) - 1
+        linespec = f"#L{lineno}-L{ending_lineno}"
+
+    repo_name = "qiskit" if "qiskit/" in str(file_name) else "qiskit-aer"
+    return f"https://github.com/Qiskit/{repo_name}/tree/{GITHUB_BRANCH}/{file_name}{linespec}"

tox.ini

@@ -10,6 +10,9 @@ setenv =
   LANGUAGE=en_US
   LC_ALL=en_US.utf-8
   SETUPTOOLS_ENABLE_FEATURES=legacy-editable
+passenv=
+  GITHUB_REF_NAME
+  GITHUB_BASE_REF
 whitelist_externals = sh
 deps =
   -r requirements-dev.txt