nodejs/node · error · RuntimeError

%s cannot provide access to the source

Error message

%s cannot provide access to the source

What it means

BaseLoader.get_source checks the class attribute has_source_access; when it is False the loader cannot expose raw template source and get_source raises RuntimeError naming the loader class. In this codebase ModuleLoader sets has_source_access = False (loaders.py:434) because it serves precompiled bytecode modules, not source.

Source

Thrown at tools/inspector_protocol/jinja2/loaders.py:89

        """Get the template source, filename and reload helper for a template.
        It's passed the environment and template name and has to return a
        tuple in the form ``(source, filename, uptodate)`` or raise a
        `TemplateNotFound` error if it can't locate the template.

        The source part of the returned tuple must be the source of the
        template as unicode string or a ASCII bytestring.  The filename should
        be the name of the file on the filesystem if it was loaded from there,
        otherwise `None`.  The filename is used by python for the tracebacks
        if no loader extension is used.

        The last item in the tuple is the `uptodate` function.  If auto
        reloading is enabled it's always called to check if the template
        changed.  No arguments are passed so the function must store the
        old state somewhere (for example in a closure).  If it returns `False`
        the template will be reloaded.
        """
        if not self.has_source_access:
            raise RuntimeError('%s cannot provide access to the source' %
                               self.__class__.__name__)
        raise TemplateNotFound(template)

    def list_templates(self):
        """Iterates over all templates.  If the loader does not support that
        it should raise a :exc:`TypeError` which is the default behavior.
        """
        raise TypeError('this loader cannot iterate over all templates')

    @internalcode
    def load(self, environment, name, globals=None):
        """Loads a template.  This method looks up the template in the cache
        or loads one by calling :meth:`get_source`.  Subclasses should not
        override this method as loaders working on collections of other
        loaders (such as :class:`PrefixLoader` or :class:`ChoiceLoader`)
        will not call this method but `get_source` directly.
        """
        code = None

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Do not call get_source on loaders where has_source_access is False; use load() to obtain a compiled Template instead.
2. Provide a source-capable loader (e.g. FileSystemLoader) alongside ModuleLoader via ChoiceLoader if source access is required.
3. Check loader.has_source_access before invoking get_source.

Example fix

# before
loader = ModuleLoader('/compiled')
src, fn, uptodate = loader.get_source(env, name)  # RuntimeError

# after
loader = ChoiceLoader([
    ModuleLoader('/compiled'),
    FileSystemLoader('/src'),
])
tmpl = env.get_template(name)  # uses load(), not get_source()

def assert_source_access(loader):
    if not getattr(loader, 'has_source_access', False):
        raise TypeError('loader %s cannot provide source; use load() instead' % type(loader).__name__)

def loader_has_source(loader) -> bool:
    return bool(getattr(loader, 'has_source_access', False))

try:
    source, fn, uptodate = loader.get_source(env, name)
except RuntimeError as e:
    if 'cannot provide access' in str(e):
        tmpl = env.get_template(name)  # fall back to load()
    else:
        raise

When it happens

Trigger: Calling loader.get_source(env, name) on a ModuleLoader (or any loader with has_source_access = False), or any code path that expects source — debugging tools, reload checks, or compile_templates introspection — against such a loader.

Common situations: Shipping precompiled templates via ModuleLoader for performance/distribution, then running tooling (debuggers, source-inspection, auto-reload) that assumes source is available.

Related errors

• no loader for this environment specified
• none of the templates given were found: %s
• {template}
• this loader cannot iterate over all templates
• The environment was not created with async mode enabled.

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/79ec98cba85cf445. Report an issue: GitHub.