When diagnosing infinite recursion references to nullptr `Env` can be formed.
This happens only with `ExprBlackHole` is evaluated, which always leads to
`InfiniteRecursionError`.
UBSAN log for one such case:
```
../src/libexpr/eval-inline.hh:94:31: runtime error: reference binding to null pointer of type 'Env'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/libexpr/eval-inline.hh:94:31 in
```
First the motivation: I recently faced a bug that I assume is coming
from the topoSortPaths function where the GC was trying to delete a
path having some alive referrers. I resolved this by manually deleting
the faulty path referrers using nix-store --query --referrers. I sadly
did not manage to reproduce this bug.
This bug alone is not a big deal. However, this bug is
triggering a cascading failure: invalidatePathChecked is throwing a
PathInUse exception. This exception is not catched and fails the whole GC
run. From there, the machine (a builder machine) was unable to GC its
Nix store, which led to an almost full disk with no way to
automatically delete the dead Nix paths.
Instead, I think we should log the error for the specific store path
we're trying to delete, specifying we can't delete this path because
it still has referrers. Once we're done with logging that, the GC run
should continue to delete the dead store paths it can delete.
This is the first part of rewriteDerivation() factored out into its
own method. It's not used anywhere else at the moment, but it's useful
on lazy-trees for rewriting virtual paths.
It's not so common knowledge that forges also expose pull requests as
git refs. But it's actually a cool way of quickly testing someones
contribution, so I found it worth specifically mentioning it.
It seems that I copied the expression for baseDir thoughtlessly and
did not come back to it.
- `baseDir` was only used in the `fromArgs` branch.
- `fromArgs` is true when `packages` is true.
This interferes with the progress bar, resulting in output like
evaluating derivation 'git+file:///home/eelco/Dev/nix-master#packages.x86_64-linux.default'/nix/store/zz8v96j5md952x0mxfix12xqnvq5qv5x-nix-2.26.0pre20241114_a95f6ea.drv
This patch gets rid of UB when verbosity exceeds the maximum logging value of `lvlVomit = 7` and
reaches invalid values (e.g. 8). This is actually triggered in functional tests.
There are too many occurrences to list, but here's one from the UBSAN log:
../src/libstore/gc.cc:610:5: runtime error: load of value 8, which is not a valid value for type 'Verbosity'
This was first tagged as 2.15.0, 1½ years ago; plenty of time for
everyone to catch up.
By now, the warning is causing more confusion than that it is helpful,
because passing a `.drv` or `drvPath` has legitimate use cases.
In these trivial cases the final vector size (or lower bound on the size) is known,
so we can avoid some vector reallocations. This is not very important, but is just
good practice and general hygiene.
This is good practice to avoid pessimisations.
Left comments for the reasoning why ctors should be noexcept.
There are some tricky cases where we intentionally want throwing move ctors/assignments.
But those cases should really be reviewed, since some of those can be replaced
with more idiomatic copy/move-and-swap.
