1 files changed, 72 insertions, 0 deletions
diff --git a/sphinx/environment/collectors/__init__.py b/sphinx/environment/collectors/__init__.py
new file mode 100644
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+++ b/sphinx/environment/collectors/__init__.py
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+"""The data collector components for sphinx.environment."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from docutils import nodes
+
+    from sphinx.application import Sphinx
+    from sphinx.environment import BuildEnvironment
+
+
+class EnvironmentCollector:
+    """An EnvironmentCollector is a specific data collector from each document.
+
+    It gathers data and stores :py:class:`BuildEnvironment
+    <sphinx.environment.BuildEnvironment>` as a database.  Examples of specific
+    data would be images, download files, section titles, metadatas, index
+    entries and toctrees, etc.
+    """
+
+    listener_ids: dict[str, int] | None = None
+
+    def enable(self, app: Sphinx) -> None:
+        assert self.listener_ids is None
+        self.listener_ids = {
+            'doctree-read':     app.connect('doctree-read', self.process_doc),
+            'env-merge-info':   app.connect('env-merge-info', self.merge_other),
+            'env-purge-doc':    app.connect('env-purge-doc', self.clear_doc),
+            'env-get-updated':  app.connect('env-get-updated', self.get_updated_docs),
+            'env-get-outdated': app.connect('env-get-outdated', self.get_outdated_docs),
+        }
+
+    def disable(self, app: Sphinx) -> None:
+        assert self.listener_ids is not None
+        for listener_id in self.listener_ids.values():
+            app.disconnect(listener_id)
+        self.listener_ids = None
+
+    def clear_doc(self, app: Sphinx, env: BuildEnvironment, docname: str) -> None:
+        """Remove specified data of a document.
+
+        This method is called on the removal of the document."""
+        raise NotImplementedError
+
+    def merge_other(self, app: Sphinx, env: BuildEnvironment,
+                    docnames: set[str], other: BuildEnvironment) -> None:
+        """Merge in specified data regarding docnames from a different `BuildEnvironment`
+        object which coming from a subprocess in parallel builds."""
+        raise NotImplementedError
+
+    def process_doc(self, app: Sphinx, doctree: nodes.document) -> None:
+        """Process a document and gather specific data from it.
+
+        This method is called after the document is read."""
+        raise NotImplementedError
+
+    def get_updated_docs(self, app: Sphinx, env: BuildEnvironment) -> list[str]:
+        """Return a list of docnames to re-read.
+
+        This methods is called after reading the whole of documents (experimental).
+        """
+        return []
+
+    def get_outdated_docs(self, app: Sphinx, env: BuildEnvironment,
+                          added: set[str], changed: set[str], removed: set[str]) -> list[str]:
+        """Return a list of docnames to re-read.
+
+        This methods is called before reading the documents.
+        """
+        return []