feat: Enable backlinks in API docs

Author: pawamoy

project/docs/css/mkdocstrings.css.jinja

@@ -24,4 +24,49 @@ a.autorefs-external::after {
 a.external:hover::after,
 a.autorefs-external:hover::after {
   background-color: var(--md-accent-fg-color);
-}
+}
+
+/* Tree-like output for backlinks. */
+.doc-backlink-list {
+  --tree-clr: var(--md-default-fg-color);
+  --tree-font-size: 1rem;
+  --tree-item-height: 1;
+  --tree-offset: 1rem;
+  --tree-thickness: 1px;
+  --tree-style: solid;
+  display: grid;
+  list-style: none !important;
+}
+
+.doc-backlink-list li > span:first-child {
+  text-indent: .3rem;
+}
+.doc-backlink-list li {
+  padding-inline-start: var(--tree-offset);
+  border-left: var(--tree-thickness) var(--tree-style) var(--tree-clr);
+  position: relative;
+  margin-left: 0 !important;
+
+  &:last-child {
+    border-color: transparent;
+  }
+  &::before{
+    content: '';
+    position: absolute;
+    top: calc(var(--tree-item-height) / 2 * -1 * var(--tree-font-size) + var(--tree-thickness));
+    left: calc(var(--tree-thickness) * -1);
+    width: calc(var(--tree-offset) + var(--tree-thickness) * 2);
+    height: calc(var(--tree-item-height)  * var(--tree-font-size));
+    border-left: var(--tree-thickness) var(--tree-style) var(--tree-clr);
+    border-bottom: var(--tree-thickness) var(--tree-style) var(--tree-clr);
+  }
+  &::after{
+    content: '';
+    position: absolute;
+    border-radius: 50%;
+    background-color: var(--tree-clr);
+    top: calc(var(--tree-item-height) / 2 * 1rem);
+    left: var(--tree-offset) ;
+    translate: calc(var(--tree-thickness) * -1) calc(var(--tree-thickness) * -1);
+  }
+}

project/mkdocs.yml.jinja

@@ -125,6 +125,7 @@ plugins:
         - https://docs.python.org/3/objects.inv
         paths: [src]
         options:
+          backlinks: tree
           docstring_options:
             ignore_init_summary: true
           docstring_section_style: list

project/pyproject.toml.jinja

@@ -104,7 +104,7 @@ ci = [
     "mkdocs-material>=9.5",
     "mkdocs-minify-plugin>=0.8",
     "mkdocs-section-index>=0.3",
-    "mkdocstrings[python]>=0.25",
+    "mkdocstrings[python]>=0.29",
     # YORE: EOL 3.10: Remove line.
     "tomli>=2.0; python_version < '3.11'",
 ]