exp run: --set-param adds new parameters to the params file

[iesahin]

Bug Report

Description

When I add an non-existent parameter after -S, it is added to params.yaml and the pipeline is run. This leads to unexpected results.

Reproduce

git clone https://github.com/iterative/example-get-started
cd example-get-started
dvc pull
virtualenv .venv
. .venv/bin/activate
pip install -r src/requirements.txt
dvc exp run -S feature.n_grams=3
git diff params.yaml

The experiment is run as normal and params.yaml has a new parameter:

diff --git a/params.yaml b/params.yaml
index e5a636f..aed2663 100644
--- a/params.yaml
+++ b/params.yaml
@@ -6,6 +6,7 @@ featurize:
   max_features: 3000
   ngrams: 2
 
+  n_grams: 3
 train:
   seed: 20170428
   n_est: 100
(END)

Note the typo in the parameter name.

The user thinks that they have changed a parameter, and no error is reported.

Expected

I'd expect parameters' existence are checked before making any modifications. So the line with

dvc exp run -S train.n_grams=3

should report that train.n_grams is not a valid parameter.

Environment information

Output of dvc doctor:

$ dvc doctor
DVC version: 2.4.3 (pip)
---------------------------------
Platform: Python 3.8.10 on Linux-5.8.0-59-generic-x86_64-with-glibc2.29
Supports: All remotes
Cache types: hardlink, symlink
Cache directory: ext4 on /dev/nvme0n1p2
Caches: local
Remotes: https
Workspace directory: ext4 on /dev/nvme0n1p2
Repo: dvc, git

[iesahin]

Seems a duplicate of #5477