Add initial attempt to keep working dir (#12327)

For Enterprise users with dedicated builders,
keeping the checkout around can make their build much faster,
especially in the case of a monorepo.

This is just a draft PR to start testing this concept.

Locally:

<img width="1137" height="360" alt="Screenshot 2025-07-16 at 2 58 48 PM"
src="https://github.com/user-attachments/assets/1deed038-b7df-4958-877e-828163e7cea3"
/>

Author: ericholscher

common

@@ -1970,6 +1970,7 @@ def add_features(sender, **kwargs):
     # Build related features
     SCALE_IN_PROTECTION = "scale_in_prtection"
     USE_S3_SCOPED_CREDENTIALS_ON_BUILDERS = "use_s3_scoped_credentials_on_builders"
+    DONT_CLEAN_BUILD = "dont_clean_build"
     BUILD_HEALTHCHECK = "build_healthcheck"
     BUILD_NO_ACKS_LATE = "build_no_acks_late"
 
@@ -2026,6 +2027,10 @@ def add_features(sender, **kwargs):
             _("Build: Use S3 scoped credentials for uploading build artifacts."),
         ),
         (
+            DONT_CLEAN_BUILD,
+            _(
+                "Build: Don't clean the build directory. Only for Enterprise users with dedicated builders."
+            ),
             BUILD_HEALTHCHECK,
             _("Build: Use background cURL healthcheck."),
         ),

readthedocs/projects/models.py

@@ -27,6 +27,18 @@
 
 def clean_build(version):
     """Clean the files used in the build of the given version."""
+    from readthedocs.projects.models import Feature
+
+    if version.project.has_feature(
+        Feature.DONT_CLEAN_BUILD,
+    ):
+        log.info(
+            "Skipping cleaning build files for project with DONT_CLEAN_BUILD feature.",
+            project_slug=version.project.slug,
+            version_slug=version.slug,
+        )
+        return
+
     del_dirs = [
         os.path.join(version.project.doc_path, dir_, version.slug)
         for dir_ in ("checkouts", "envs", "conda", "artifacts")

readthedocs/projects/tasks/utils.py

@@ -1,5 +1,6 @@
 """Git-related utilities."""
 
+import os
 import re
 from typing import Iterable
 from urllib.parse import urlparse
@@ -43,6 +44,14 @@ def update(self):
         """Clone and/or fetch remote repository."""
         super().update()
 
+        # Check for existing checkout and skip clone if it exists.
+        from readthedocs.projects.models import Feature
+
+        if self.project.has_feature(Feature.DONT_CLEAN_BUILD) and os.path.exists(
+            os.path.join(self.working_dir, ".git")
+        ):
+            return self.fetch()
+
         self.clone()
         # TODO: We are still using return values in this function that are legacy.
         # This should be either explained or removed.