diff: ERROR: unexpected error - 'not in cache'

Description

When I tried to compare two commits I get an error.

The command is: dvc diff f0c0269 16ba2cd I’m using your sample repo: https://github.com/iterative/example-get-started

Reproduce

Command 1 (compare commit with previous “dvc add” commit):

dvc diff f0c0269 16ba2cd

Output:

ERROR: unexpected error - 'not in cache'                              

Having any troubles? Hit us up at https://dvc.org/support, we are always happy to help!

Command 2 (compare commit with a commit before “dvc add” commit):

dvc diff 3e07290 16ba2cd

Output:

Added:                                                                
    data/data.xml

files summary: 1 added

How to reproduce it:

git clone https://github.com/iterative/example-get-started
cd example-get-started/
dvc diff 16ba2cd f0c0269

Expected

These are the first commits in your sample repo:

* 08a3b89 - (tag: 4-import-data) Import raw data (overwrite) (2021-05-20 23:56:52 -0400) <Olivaw Owlet>
* 16ba2cd - (tag: 3-config-remote) Configure default remote (2021-05-19 20:10:12 -0400) <Olivaw Owlet>
* f0c0269 - (tag: 2-track-data) Add raw data (2021-05-18 16:23:32 -0400) <Olivaw Owlet>
* 3e07290 - (tag: 1-dvc-init) Initialize DVC project (2021-05-17 12:36:52 -0400) <Olivaw Owlet>
* 90b2aea - (tag: 0-git-init) Initialize Git repository (2021-05-16 08:50:12 -0400) <Olivaw Owlet>

If you show changes on the third commit f0c0269 with git show f0c0269 you can see:

commit f0c026993d3dc8aa4d79426acb59b81dbb63e5a2 (tag: 2-track-data)
Author: Olivaw Owlet <[e-mail]>
Date:   Tue May 18 16:23:32 2021 -0400

    Add raw data

diff --git a/data/.gitignore b/data/.gitignore
new file mode 100644
index 0000000..fc12be5
--- /dev/null
+++ b/data/.gitignore
@@ -0,0 +1 @@
+/data.xml
diff --git a/data/data.xml.dvc b/data/data.xml.dvc
new file mode 100644
index 0000000..8fab3a9
--- /dev/null
+++ b/data/data.xml.dvc
@@ -0,0 +1,5 @@
+outs:
+- md5: a304afb96060aad90176268345e10355
+  size: 37891850
+  path: data.xml
+  desc: Initial XML StackOverflow dataset (raw data)

I suppose that means that was the commit where the file data\data.xml was added using dvc.

What I expect:

If I create a commit adding a file with dvc add and I compare the next commit with the previous one I expect the dvc diff two show that the file was added.

That means I expect the command 1 to have to same output as command 2 because the file was added in the commit f0c0269

Environment information

Output of `dvc diff -v f0c0269 16ba2cd:

2021-09-30 17:03:09,704 ERROR: unexpected error - 'not in cache'      
------------------------------------------------------------
Traceback (most recent call last):
  File "/home/josecelano/anaconda3/lib/python3.8/site-packages/dvc/main.py", line 55, in main
    ret = cmd.do_run()
  File "/home/josecelano/anaconda3/lib/python3.8/site-packages/dvc/command/base.py", line 45, in do_run
    return self.run()
  File "/home/josecelano/anaconda3/lib/python3.8/site-packages/dvc/command/diff.py", line 131, in run
    del diff["not in cache"]
KeyError: 'not in cache'
------------------------------------------------------------
2021-09-30 17:03:09,891 DEBUG: Version info for developers:
DVC version: 2.7.3 (pip)
---------------------------------
Platform: Python 3.8.8 on Linux-5.10.0-1045-oem-x86_64-with-glibc2.10
Supports:
	azure (adlfs = 2021.9.1, knack = 0.8.2, azure-identity = 1.6.1),
	http (aiohttp = 3.7.4.post0, aiohttp-retry = 2.4.5),
	https (aiohttp = 3.7.4.post0, aiohttp-retry = 2.4.5)
Cache types: <https://error.dvc.org/no-dvc-cache>
Caches: local
Remotes: https
Workspace directory: ext4 on /dev/mapper/vgubuntu-root
Repo: dvc, git

Having any troubles? Hit us up at https://dvc.org/support, we are always happy to help!
2021-09-30 17:03:09,892 DEBUG: Analytics is enabled.
2021-09-30 17:03:09,926 DEBUG: Trying to spawn '['daemon', '-q', 'analytics', '/tmp/tmpx7a6ek24']'
2021-09-30 17:03:09,927 DEBUG: Spawned '['daemon', '-q', 'analytics', '/tmp/tmpx7a6ek24']'

[dberenbaum]

That means I expect the command 1 to have to same output as command 2 because the file was added in the commit f0c0269

Since the data.xml.dvc exists in f0c0269 but not in 3e07290, these shouldn’t have the same output, right @josecelano? I would expect dvc diff f0c0269 16ba2cd to return nothing. I think https://github.com/Nautilus-Cyberneering/chinese-ideographs/issues/38 sums it up: dvc diff fails when no files have been changed.

For example:

$ dvc diff 16ba2cd 08a3b89
2022-02-17 13:51:57,963 ERROR: unexpected error - 'not in cache'
------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/dave/Code/dvc/dvc/cli/__init__.py", line 78, in main
    ret = cmd.do_run()
  File "/Users/dave/Code/dvc/dvc/cli/command.py", line 22, in do_run
    return self.run()
  File "/Users/dave/Code/dvc/dvc/commands/diff.py", line 131, in run
    del diff["not in cache"]
KeyError: 'not in cache'
------------------------------------------------------------

@efiop The error isn’t related to #6594 or dvc/repo/diff.py.

https://github.com/iterative/dvc/blob/0b18efb7b7cea1d2b76d1ab450266b1551eeee84/dvc/commands/diff.py#L131

This line simply doesn’t handle the case where that key doesn’t exist. Do you want me to submit a PR?

[josecelano]

OK thank you @efiop for your fast reply. It seems this kind of references do not work either:

dvc diff refs/remotes/origin/main^ other-branch

I’m trying to apply a “hack” to get the previous commit.