import-url/update: add --no-download flag

add --no-download flag to dvc import-url/dvc update to only create/update .dvc
files without downloading the associated data.

Created .dvc files can be fetched using `dvc pull` or can be
updated using `dvc update --no-download`.

dvc/commands/imp.py

@@ -19,6 +19,7 @@ def run(self):
                 fname=self.args.file,
                 rev=self.args.rev,
                 no_exec=self.args.no_exec,
+                no_download=self.args.no_download,
                 desc=self.args.desc,
                 jobs=self.args.jobs,
             )
@@ -69,11 +70,19 @@ def add_parser(subparsers, parent_parser):
         help="Specify name of the .dvc file this command will generate.",
         metavar="<filename>",
     )
-    import_parser.add_argument(
+    no_download_exec_group = import_parser.add_mutually_exclusive_group()
+    no_download_exec_group.add_argument(
         "--no-exec",
         action="store_true",
         default=False,
-        help="Only create .dvc file without actually downloading it.",
+        help="Only create .dvc file without actually importing target data.",
+    )
+    no_download_exec_group.add_argument(
+        "--no-download",
+        action="store_true",
+        default=False,
+        help="Create .dvc file including target data hash value(s)"
+        " but do not actually download the file(s).",
     )
     import_parser.add_argument(
         "--desc",

dvc/commands/imp_url.py

@@ -17,6 +17,7 @@ def run(self):
                 out=self.args.out,
                 fname=self.args.file,
                 no_exec=self.args.no_exec,
+                no_download=self.args.no_download,
                 remote=self.args.remote,
                 to_remote=self.args.to_remote,
                 desc=self.args.desc,
@@ -66,11 +67,19 @@ def add_parser(subparsers, parent_parser):
         help="Specify name of the .dvc file this command will generate.",
         metavar="<filename>",
     ).complete = completion.DIR
-    import_parser.add_argument(
+    no_download_exec_group = import_parser.add_mutually_exclusive_group()
+    no_download_exec_group.add_argument(
         "--no-exec",
         action="store_true",
         default=False,
-        help="Only create .dvc file without actually downloading it.",
+        help="Only create .dvc file without actually importing target data.",
+    )
+    no_download_exec_group.add_argument(
+        "--no-download",
+        action="store_true",
+        default=False,
+        help="Create .dvc file including target data hash value(s)"
+        " but do not actually download the file(s).",
     )
     import_parser.add_argument(
         "--to-remote",

dvc/commands/update.py

@@ -18,6 +18,7 @@ def run(self):
                 rev=self.args.rev,
                 recursive=self.args.recursive,
                 to_remote=self.args.to_remote,
+                no_download=self.args.no_download,
                 remote=self.args.remote,
                 jobs=self.args.jobs,
             )
@@ -55,6 +56,13 @@ def add_parser(subparsers, parent_parser):
         default=False,
         help="Update all stages in the specified directory.",
     )
+    update_parser.add_argument(
+        "--no-download",
+        action="store_true",
+        default=False,
+        help="Update .dvc file hash value(s)"
+        " but do not download the file(s).",
+    )
     update_parser.add_argument(
         "--to-remote",
         action="store_true",

dvc/output.py

@@ -375,6 +375,11 @@ def __str__(self):
 
         return self.fs.path.relpath(self.fs_path, self.repo.root_dir)
 
+    def clear(self):
+        self.hash_info = HashInfo.from_dict({})
+        self.meta = Meta.from_dict({})
+        self.obj = None
+
     @property
     def protocol(self):
         return self.fs.protocol

dvc/repo/__init__.py

@@ -3,7 +3,7 @@
 from collections import defaultdict
 from contextlib import contextmanager
 from functools import wraps
-from typing import TYPE_CHECKING, Callable, Optional
+from typing import TYPE_CHECKING, Callable, List, Optional
 
 from funcy import cached_property
 
@@ -18,6 +18,7 @@
     from dvc.fs import FileSystem
     from dvc.repo.scm_context import SCMContext
     from dvc.scm import Base
+    from dvc.stage import Stage
 
 logger = logging.getLogger(__name__)
 
@@ -444,6 +445,44 @@ def used_objs(
 
         return used
 
+    def partial_imports(
+        self,
+        targets=None,
+        all_branches=False,
+        all_tags=False,
+        all_commits=False,
+        all_experiments=False,
+        commit_date: Optional[str] = None,
+        recursive=False,
+        revs=None,
+        num=1,
+    ) -> List["Stage"]:
+        """Get the stages related to the given target and collect dependencies
+        which are missing outputs.
+
+        This is useful to retrieve files which have been imported to the repo
+        using --no-download.
+
+        Returns:
+            A list of partially imported stages
+        """
+        from itertools import chain
+
+        partial_imports = chain.from_iterable(
+            self.index.partial_imports(targets, recursive=recursive)
+            for _ in self.brancher(
+                revs=revs,
+                all_branches=all_branches,
+                all_tags=all_tags,
+                all_commits=all_commits,
+                all_experiments=all_experiments,
+                commit_date=commit_date,
+                num=num,
+            )
+        )
+
+        return list(partial_imports)
+
     @property
     def stages(self):  # obsolete, only for backward-compatibility
         return self.index.stages

dvc/repo/fetch.py

@@ -93,6 +93,18 @@ def fetch(
             downloaded += d
             failed += f
 
+    d, f = _fetch_partial_imports(
+        self,
+        targets,
+        all_branches=all_branches,
+        all_tags=all_tags,
+        all_commits=all_commits,
+        recursive=recursive,
+        revs=revs,
+    )
+    downloaded += d
+    failed += f
+
     if failed:
         raise DownloadError(failed)
 
@@ -107,3 +119,25 @@ def _fetch(repo, obj_ids, **kwargs):
     except FileTransferError as exc:
         failed += exc.amount
     return downloaded, failed
+
+
+def _fetch_partial_imports(repo, targets, **kwargs):
+    from dvc.stage.exceptions import DataSourceChanged
+
+    downloaded = 0
+    failed = 0
+    for stage in repo.partial_imports(targets, **kwargs):
+        try:
+            stage.run()
+        except DataSourceChanged as exc:
+            logger.warning(f"{exc}")
+            failed += 1
+            continue
+        if not any(
+            kwargs.get(kw, None)
+            for kw in ("all_branches", "all_tags", "all_commits", "revs")
+        ):
+            stage.dump()
+
+        downloaded += 1
+    return downloaded, failed

dvc/repo/imp_url.py

@@ -17,6 +17,7 @@ def imp_url(
     fname=None,
     erepo=None,
     frozen=True,
+    no_download=False,
     no_exec=False,
     remote=None,
     to_remote=False,
@@ -31,9 +32,9 @@ def imp_url(
         self, out, always_local=to_remote and not out
     )
 
-    if to_remote and no_exec:
+    if to_remote and (no_exec or no_download):
         raise InvalidArgumentError(
-            "--no-exec can't be combined with --to-remote"
+            "--no-exec/--no-download cannot be combined with --to-remote"
         )
 
     if not to_remote and remote:
@@ -80,7 +81,7 @@ def imp_url(
         stage.save_deps()
         stage.md5 = stage.compute_md5()
     else:
-        stage.run(jobs=jobs)
+        stage.run(jobs=jobs, no_download=no_download)
 
     stage.frozen = frozen
 

dvc/repo/index.py

@@ -246,6 +246,28 @@ def used_objs(
                 used[odb].update(objs)
         return used
 
+    def partial_imports(
+        self,
+        targets: "TargetType" = None,
+        recursive: bool = False,
+    ) -> List["Stage"]:
+        from itertools import chain
+
+        from dvc.utils.collections import ensure_list
+
+        collect_targets: Sequence[Optional[str]] = (None,)
+        if targets:
+            collect_targets = ensure_list(targets)
+
+        pairs = chain.from_iterable(
+            self.stage_collector.collect_granular(
+                target, recursive=recursive, with_deps=True
+            )
+            for target in collect_targets
+        )
+
+        return [stage for stage, _ in pairs if stage.is_partial_import]
+
     # Following methods help us treat the collection as a set-like structure
     # and provides faux-immutability.
     # These methods do not preserve stages order.

dvc/repo/update.py

@@ -10,6 +10,7 @@ def update(
     rev=None,
     recursive=False,
     to_remote=False,
+    no_download=False,
     remote=None,
     jobs=None,
 ):
@@ -21,6 +22,11 @@ def update(
     if isinstance(targets, str):
         targets = [targets]
 
+    if to_remote and no_download:
+        raise InvalidArgumentError(
+            "--to-remote can't be used with --no-download"
+        )
+
     if not to_remote and remote:
         raise InvalidArgumentError(
             "--remote can't be used without --to-remote"
@@ -31,7 +37,13 @@ def update(
         stages.update(self.stage.collect(target, recursive=recursive))
 
     for stage in stages:
-        stage.update(rev, to_remote=to_remote, remote=remote, jobs=jobs)
+        stage.update(
+            rev,
+            to_remote=to_remote,
+            remote=remote,
+            no_download=no_download,
+            jobs=jobs,
+        )
         dvcfile = Dvcfile(self, stage.path)
         dvcfile.dump(stage)