nix-collect-garbage `--dry-run` flag has incorrect behaviour #432

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opened 2024-07-05 16:57:12 +00:00 by quantumbjump · 2 comments

quantumbjump commented

2024-07-05 16:57:12 +00:00

Describe the bug

The --dry-run flag in nix-collect-garbage doesn't print out unused nix store paths, as I would expect from a dry run. The code here means that if you pass the --dry-run flag, it completely skips the entire body of the script and just returns 0.

Steps To Reproduce

Have a nix store with some dead paths
Run nix-collect-garbage --dry-run
See no output (implying that there's nothing to garbage collect)
Run nix-collect-garbage
See that it does delete the dead paths

Expected behavior

nix-collect-garbage --dry-run should print the paths that would be deleted, and then not delete them.

`nix --version` output

nix (Lix, like Nix) 2.91.0-dev-pre20240704-d00edfb

Additional context

I'm not well versed in C++, but this seems like it should be a relatively easy fix. The GCOptions struct has a gcReturnDead action, which should return the list of paths that would be deleted instead of actually deleting them. It should be as simple as setting the action to gcReturnDead if the dryRun flag is set, and gcDeleteDead if it isn't.

## Describe the bug The `--dry-run` flag in `nix-collect-garbage` doesn't print out unused nix store paths, as I would expect from a dry run. The code [here](https://git.lix.systems/lix-project/lix/src/branch/main/src/nix-collect-garbage/nix-collect-garbage.cc#L91) means that if you pass the `--dry-run` flag, it completely skips the entire body of the script and just returns 0. ## Steps To Reproduce 1. Have a nix store with some dead paths 2. Run `nix-collect-garbage --dry-run` 3. See no output (implying that there's nothing to garbage collect) 4. Run `nix-collect-garbage` 5. See that it does delete the dead paths ## Expected behavior `nix-collect-garbage --dry-run` should print the paths that *would* be deleted, and then not delete them. ## `nix --version` output `nix (Lix, like Nix) 2.91.0-dev-pre20240704-d00edfb` ## Additional context I'm not well versed in C++, but this seems like it should be a relatively easy fix. The GCOptions struct has a `gcReturnDead` action, which should return the list of paths that would be deleted instead of actually deleting them. It *should* be as simple as setting the action to `gcReturnDead` if the `dryRun` flag is set, and `gcDeleteDead` if it isn't.

quantumbjump added the

bug

label 2024-07-05 16:57:12 +00:00

lix-bot commented

2024-07-05 19:36:37 +00:00

Member

This issue was mentioned on Gerrit on the following CLs:

commit message in cl/1566 ("Fix dry-run flag for nix-collect-garbage")

This issue was mentioned on Gerrit on the following CLs: * commit message in [cl/1566](https://gerrit.lix.systems/c/lix/+/1566) ("Fix dry-run flag for nix-collect-garbage")