experiments: disable feature by default

* experiments only enabled in test environment (DVC_TEST) or when
  core.experiments config option is true

dvc/command/experiments.py

@@ -114,6 +114,9 @@ def run(self):
         from rich.console import Console
         from dvc.utils.pager import pager
 
+        if not self.repo.experiments:
+            return 0
+
         try:
             all_experiments = self.repo.experiments.show(
                 all_branches=self.args.all_branches,
@@ -139,6 +142,9 @@ def run(self):
 
 class CmdExperimentsCheckout(CmdBase):
     def run(self):
+        if not self.repo.experiments:
+            return 0
+
         self.repo.experiments.checkout(
             self.args.experiment, force=self.args.force
         )
@@ -185,6 +191,9 @@ def _round(val):
 
 class CmdExperimentsDiff(CmdBase):
     def run(self):
+        if not self.repo.experiments:
+            return 0
+
         try:
             diff = self.repo.experiments.diff(
                 a_rev=self.args.a_rev,

dvc/config.py

@@ -127,6 +127,7 @@ class RelPath(str):
         Optional("analytics", default=True): Bool,
         Optional("hardlink_lock", default=False): Bool,
         Optional("no_scm", default=False): Bool,
+        Optional("experiments", default=False): Bool,
     },
     "cache": {
         "local": str,

dvc/repo/__init__.py

@@ -127,7 +127,10 @@ def __init__(self, root_dir=None, scm=None, rev=None):
         self.plots = Plots(self)
         self.params = Params(self)
 
-        self.experiments = Experiments(self)
+        try:
+            self.experiments = Experiments(self)
+        except NotImplementedError:
+            self.experiments = None
 
         self._ignore()
 
@@ -196,8 +199,9 @@ def _ignore(self):
         flist = [
             self.config.files["local"],
             self.tmp_dir,
-            self.experiments.exp_dir,
         ]
+        if self.experiments:
+            flist.append(self.experiments.exp_dir)
 
         if path_isin(self.cache.local.cache_dir, self.root_dir):
             flist += [self.cache.local.cache_dir]

dvc/repo/experiments/__init__.py

@@ -8,7 +8,7 @@
 from dvc.exceptions import DvcException
 from dvc.scm.git import Git
 from dvc.stage.serialize import to_lockfile
-from dvc.utils import dict_sha256, relpath
+from dvc.utils import dict_sha256, env2bool, relpath
 from dvc.utils.fs import remove
 
 logger = logging.getLogger(__name__)
@@ -28,6 +28,12 @@ class Experiments:
     EXPERIMENTS_DIR = "experiments"
 
     def __init__(self, repo):
+        if not (
+            env2bool("DVC_TEST")
+            or repo.config["core"].get("experiments", False)
+        ):
+            raise NotImplementedError
+
         self.repo = repo
 
     @cached_property

dvc/repo/reproduce.py

@@ -71,7 +71,7 @@ def reproduce(
         )
 
     experiment = kwargs.pop("experiment", False)
-    if experiment:
+    if experiment and self.experiments:
         try:
             return self.experiments.new(
                 target=target,