🔧 MAINTAIN: Add feature flag for lazy loading (#35)

docs/configure.md

@@ -173,7 +173,7 @@ By default, Thebe encourages users to use the `thebe-button` directive to
 insert a thebe button into their documentation. However, you can add your own
 buttons wherever you wish. Simply ensure that an HTML element has this attribute:
 
-```
+```js
 onclick="initThebe()"
 ```
 
@@ -193,7 +193,7 @@ directive:
 You can customize `sphinx-thebe` to use the codemirror theme of your choice.
 To do so, use the following configuration:
 
-```
+```python
 thebe_config = {
    "codemirror-theme": "<cm-theme>"
 }
@@ -202,15 +202,27 @@ thebe_config = {
 See [the CodeMirror theme demo](https://codemirror.net/demo/theme.html) for a list
 of themes that you can use, and what they look like.
 
+## Only load JS on certain pages
+
+By default, `sphinx-thebe` will load the JS/CSS from `thebe` on all of your documentation's pages.
+Alternatively, you may load `thebe` only on pages that use the `thebe-button` directive.
+To do so, use the following configuration:
+
+```python
+thebe_config = {
+   "always_load": False
+}
+```
 
 ## Configuration reference
 
 Here's a reference of all of the configuration values avialable to `sphinx-thebe`.
 Many of these eventually make their was into the `thebe` configuration. You can
 find a [reference for `thebe` configuration here](https://thebelab.readthedocs.io/en/latest/config_reference.html).
 
-```
+```python
 thebe_config = {
+    "always_load": bool (default True)
     "repository_url": "<your-repo-url>",
     "repository_branch": "<your-repo-branch>",
     "selector": "<selector-for-code-cells>",

sphinx_thebe/__init__.py

@@ -23,6 +23,7 @@ def st_static_path(app):
 def init_thebe_default_config(app, env, docnames):
     thebe_config = app.config.thebe_config
     defaults = {
+        "always_load": True,
         "selector": ".thebe",
         "selector_input": "pre",
         "selector_output": ".output",
@@ -32,28 +33,41 @@ def init_thebe_default_config(app, env, docnames):
             thebe_config[key] = val
 
 
-def _check_if_load_thebe(doctree, config_thebe):
+def _bool(b):
+    if isinstance(b, bool):
+        return b
+    else:
+        return b in ["true", "True"]
+
+
+def _do_load_thebe(doctree, config_thebe):
     """Decide whether to load thebe based on the page's context."""
-    # Only load `thebe` if there is a thebe button somewhere
-    if not doctree or (not doctree.traverse(ThebeButtonNode)):
-        return
+    if not doctree:
+        return False
 
+    # If we aren't properly configured
     if not config_thebe:
         logger.warning("Didn't find `thebe_config` in conf.py, add to use thebe")
-        return
+        return False
 
-    return True
+    # Only load `thebe` if there is a thebe button somewhere
+    if doctree.traverse(ThebeButtonNode) or _bool(config_thebe.get("always_load")):
+        return True
+    else:
+        return False
 
 
 def init_thebe_core(app, pagename, templatename, context, doctree):
     """Load thebe assets if there's a thebe button on this page."""
     config_thebe = app.config["thebe_config"]
-    if not _check_if_load_thebe(doctree, config_thebe):
+    if not _do_load_thebe(doctree, config_thebe):
         return
 
     # Add core libraries
     opts = {"async": "async"}
-    app.add_js_file(filename=f"https://unpkg.com/thebe@{THEBE_VERSION}/lib/index.js", **opts)
+    app.add_js_file(
+        filename=f"https://unpkg.com/thebe@{THEBE_VERSION}/lib/index.js", **opts
+    )
 
     # Add configuration variables
     thebe_config = f"""
@@ -68,7 +82,7 @@ def init_thebe_core(app, pagename, templatename, context, doctree):
 def update_thebe_context(app, doctree, docname):
     """Add thebe config nodes to this doctree."""
     config_thebe = app.config["thebe_config"]
-    if not _check_if_load_thebe(doctree, config_thebe):
+    if not _do_load_thebe(doctree, config_thebe):
         return
 
     # Thebe configuration
@@ -208,11 +222,13 @@ def setup(app):
 
     # Update the doctree with thebe-specific information if needed
     app.connect("doctree-resolved", update_thebe_context)
-    # Load the JS/CSS assets for thebe if needed    
+
+    # Load the JS/CSS assets for thebe if needed
     app.connect("html-page-context", init_thebe_core)
 
     # configuration for this tool
     app.add_config_value("thebe_config", {}, "html")
+
     # override=True in case Jupyter Sphinx has already been loaded
     app.add_directive("thebe-button", ThebeButton, override=True)
 

tests/test_build.py

@@ -18,6 +18,7 @@ class SphinxBuild:
         path_html = path_build.joinpath("html")
         path_pg_index = path_html.joinpath("index.html")
         path_pg_config = path_html.joinpath("configure.html")
+        path_pg_chglg = path_html.joinpath("changelog.html")
         cmd_base = ["sphinx-build", ".", "_build/html", "-a", "-W"]
 
         def copy(self, path=None):
@@ -68,3 +69,26 @@ def test_sphinx_thebe(file_regression, sphinx_build):
     launch_buttons = soup_conf.select(".thebe-launch-button")
     lb_text = "\n\n".join([ii.prettify() for ii in launch_buttons])
     file_regression.check(lb_text, basename="launch_buttons", extension=".html")
+
+    # Changelog has no thebe button directive, but should have the JS anyway
+    soup_chlg = BeautifulSoup(
+        Path(sphinx_build.path_pg_chglg).read_text(), "html.parser"
+    )
+    assert "https://unpkg.com/thebe" in soup_chlg.prettify()
+
+
+def test_always_load(file_regression, sphinx_build):
+    """Test building with thebe."""
+    sphinx_build.copy()
+
+    # Basic build with defaults
+    sphinx_build.build(cmd=["-D", "thebe_config.always_load=false"])
+
+    # Thebe should be loaded on a page *with* the directive and not on pages w/o it
+    soup_ix = BeautifulSoup(Path(sphinx_build.path_pg_index).read_text(), "html.parser")
+    assert "https://unpkg.com/thebe" in soup_ix.prettify()
+    # Changelog has no thebe button directive, so shouldn't have JS
+    soup_chlg = BeautifulSoup(
+        Path(sphinx_build.path_pg_chglg).read_text(), "html.parser"
+    )
+    assert "https://unpkg.com/thebe" not in soup_chlg.prettify()