Recently, I encountered the "NAR info file 'xxxx' is corrupt" error
with my binary cache. The message is not helpful in determining, which
kind of corruption happened. The file, fetched with curl, looked
reasonably.
This commit adds more information to the error message, which should
allow debugging and hopefully fixing the problem.
We finally test the status quo of remote build trust in a number of
ways. We create a new experimental feature on `nix-daemon` to do so.
PR #3921, which improves the situation with trustless remote building,
will build upon these changes. This code / tests was pull out of there
to make this, so everything is easier to review, and in particular we
test before and after so the new behavior in that PR is readily apparent
from the testsuite diff alone.
Issues:
1. Features gated on disabled experimental settings should warn and be
ignored, not silently succeed.
2. Experimental settings in the same config "batch" (file or env var)
as the enabling of the experimental feature should work.
3. For (2), the order should not matter.
These are analogous to the issues @roberth caught with my changes for
arg handling, but they are instead for config handling.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
In many cases we are dealing with a collection of realisations, they are
all outputs of the same derivation. In that case, we don't need
"derivation hashes modulos" to be part of our map key, because the
output names alone will be unique. Those hashes are still part of the
realisation proper, so we aren't loosing any information, we're just
"normalizing our schema" by narrowing the "primary key".
Besides making our data model a bit "tighter" this allows us to avoid a
double `for` loop in `DerivationGoal::waiteeDone`. The inner `for` loop
was previously just to select the output we cared about without knowing
its hash. Now we can just select the output by name directly.
Note that neither protocol is changed as part of this: we are still
transferring `DrvOutputs` over the wire for `BuildResult`s. I would only
consider revising this once #6223 is merged, and we can mention protocol
versions inside factored-out serialization logic. Until then it is
better not change anything because it would come a the cost of code
reuse.
If my memory is correct, @edolstra objected to modifying `wantedOutputs`
upon falling back to doing a build (as we did before), because we should
only modify it in response to new requests --- *actual* wants --- and
not because we are "incidentally" building all the outptus beyond what
may have been requested.
That's a fair point, and the alternative is to replace the boolean soup
with proper enums: Instead of modifying `wantedOuputs` som more, we'll
modify `needsRestart` to indicate we are passed the need.
In https://github.com/NixOS/nix/pull/6311#discussion_r834863823, I
realized since derivation goals' wanted outputs can "grow" due to
overlapping dependencies (See `DerivationGoal::addWantedOutputs`, called
by `Worker::makeDerivationGoalCommon`), the previous bug fix had an
unfortunate side effect of causing more pointless rebuilds.
In paticular, we have this situation:
1. Goal made from `DerivedPath::Built { foo, {a} }`.
2. Goal gives on on substituting, starts building.
3. Goal made from `DerivedPath::Built { foo, {b} }`, in fact is just
modified original goal.
4. Though the goal had gotten as far as building, so all outputs were
going to be produced, `addWantedOutputs` no longer knows that and so
the goal is flagged to be restarted.
This might sound far-fetched with input-addressed drvs, where we usually
basically have all our goals "planned out" before we start doing
anything, but with CA derivation goals and especially RFC 92, where *drv
resolution* means goals are created after some building is completed, it
is more likely to happen.
So the first thing to do was restore the clearing of `wantedOutputs` we
used to do, and then filter the outputs in `buildPathsWithResults` to
only get the ones we care about.
But fix also has its own side effect in that the `DerivedPath` in the
`BuildResult` in `DerivationGoal` cannot be trusted; it is merely the
*first* `DerivedPath` for which this goal was originally created.
To remedy this, I made `BuildResult` be like it was before, and instead
made `KeyedBuildResult` be a subclass wit the path. Only
`buildPathsWithResults` returns `KeyedBuildResult`s, everything else
just becomes like it was before, where the "key" is unambiguous from
context.
I think separating the "primary key" field(s) from the other fields is
good practical in general anyways. (I would like to do the same thing
for `ValidPathInfo`.) Among other things, it allows constructions like
`std::map<Key, ThingWithKey>` where doesn't contain duplicate keys and
just precludes the possibility of those duplicate keys being out of
sync.
We might leverage the above someday to overload `buildPathsWithResults`
to take a *set* of return a *map* per the above.
-----
Unfortunately, we need to avoid C++20 strictness on designated
initializers.
(BTW
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2287r1.html
this offers some new syntax for this use-case. Hopefully this will be
adopted and we can eventually use it.)
No having that yet, maybe it would be better to not make
`KeyedBuildResult` a subclass to just avoid this.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
As requested by @roberth, it is good to call out the specific instances
we care about, which is `!` for the RPC protocols, and `^` for humans.
This doesn't take advantage of parametricity as much, but since the
human and computer interfaces are good to decouple anyways (we don't
care if they drift further apart over time in the slightest) some
separation and slight duplication is fine.
Also, unit test both round trips.
More progress on issue #5729
The method trivially generalizes to be store-implementation-agnostic, in
fact.
However, we force it to continue to be unimplemented with `RemoteStore`
and `LegacySSHStore` because the implementation we'd get via the
generalization is probably not the one users expect. This keeps our
hands untied to do it right going forward.
For more about the tension between the scheduler logic being
store-type-agnostic and remote stores doing their own scheduling, see
issues #5025 and #5056.
- Create a glossary entry for experimental features.
- Have the man page experimental feature notice link `nix-commmand`.
(Eventually this should be programmed, based on whether the command is
experimental, and if so what experimental feature does it depend on.)
- Document which installables depend on which experimental features.
I tried to use the same style (bold warning and block quote) that the
top of the man page uses.
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
The warning message should produce an installable name that can be
passed to `nix build`, `nix path-info`, etc. again. Since the CLI
expects that the .drv path and the output names are separated by
a caret, the warning message must also separate the .drv path and output
names with a caret.
However, `DerivedPath::Built.to_string()` uses an exclamation point as
the separator instead. This commit adds a `separator` argument to the
to_string method.
This changes the warning message from:
If this command is now failing try again with '/nix/store/foo.drv!*'
to:
If this command is now failing try again with '/nix/store/foo.drv^*'
More progress on issue #5729.
Instead of having it by the default method in `Store` itself, have it be
the implementation in `DummyStore` and `LegacySSHStore`. Then just the
implementations which fail to provide the method pay the "penalty" of
dealing with the icky `unimplemented` function for non-compliance.
Combined with my other recent PRs, this finally makes `Store` have no
`unsupported` calls!
This is somewhat hacky fix just for 2.15. I unintentionally hid them
from the manual, when no one wanted to hide them that (including
myself). I also required the experimental feature to be enabled in an
order-dependent way, which is not good.
The simplest fix for this immanent release is just to always show them,
and always allow them to be set.
Effectively undoes some changes from aa663b7e89
Getting the occasional SQLITE_BUSY is expected when the database is being
accessed concurrently. The retry will likely succeed so it is pointless to warn
immediately. Instead we track how long each retrySQLite block has been running,
and only begin warning after a second has elapsed (and then every 10 seconds
subsequently).
Some of the factoring out was taken from #7912 by @mupdt. Thanks!
No behavior should be changed in this commit.
Co-Authored-By: mupdt <25388474+mupdt@users.noreply.github.com>
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
How signals should be handled depends on what kind of process Nix
is integrated into. The signal handler thread used by the stand-alone
Nix commands / processes may not work well in the context of other
runtime systems, such as those of Python, Perl, or Haskell.
libutil is a dependency of libstore, so it should always be
initialized as such.
libutil is also a dependency of libmain. Being explicit about this
dependency might be good, but not worth the slight code complexity
until the library structure gets more advanced.
Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.
Quote
Why not initLibExpr()? initGC() is essentially that, but
detectStackOverflow is not an instance of the init function concept, as
it may have to be invoked more than once per process.
Furthermore, renaming initGC to initLibExpr is more trouble than it's
worth at this time.
This code is bad. We shouldn't unset variables in programs whose
children may need them. Fixing one issue at a time, so postponing.
See https://github.com/NixOS/nix/issues/7731
Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.
It is required for the sandbox, which is a libstore responsibility;
not just libmain.
Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.
Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.
The goal of this reordering is to make initLibStore self-sufficient
in a following commit.
Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.
Using libstore without loading the config file is risky, as sqlite
may then be misconfigured. See https://github.com/cachix/cachix/issues/475
* Finish converting existing comments for internal API docs
99% of this was just reformatting existing comments. Only two exceptions:
- Expanded upon `BuildResult::status` compat note
- Split up file-level `symbol-table.hh` doc comments to get
per-definition docs
Also fixed a few whitespace goofs, turning leading tabs to spaces and
removing trailing spaces.
Picking up from #8133
* Fix two things from comments
* Use triple-backtick not indent for `dumpPath`
* Convert GNU-style `\`..'` quotes to markdown style in API docs
This will render correctly.
This is non-breaking change in the to-JSON direction. This *is* a
breaking change in the from-JSON direction, but we don't care, as that
is brand new in this PR.
`nix show-derivation --help` currently has the sole public documentation
of this format, it is updated accordingly.
The `write` name is ambiguous and could lead to some funny bugs like
https://github.com/NixOS/nix/pull/8173#issuecomment-1500009480. So
rename it to the more explicit `writeUnbuffered`.
Besides, this method shouldn't be (and isn't) used outside of the class
implementation, so mark it `protected`.
This makes it more symetrical to `BufferedSource` which uses a
`protected readUnbuffered` method.
This function returns true or false depending on whether the Nix client
is trusted or not. Mostly relevant when speaking to a remote store with
a daemon.
We include this information in `nix ping store` and `nix doctor`
Co-Authored-By: John Ericson <John.Ericson@Obsidian.Systems>
They are put in the manual separate pages under the new overarching
description of experimental features.
The settings page just lists the valid experimental feature names (so
people know what a valid setting entry looks like), with links to those
pages. It doesn't attempt to describe each experimental feature as that
is too much information for the configuration settings section.
This introduces the SourcePath type from lazy-trees as an abstraction
for accessing files from inputs that may not be materialized in the
real filesystem (e.g. Git repositories). Currently, however, it's just
a wrapper around CanonPath, so it shouldn't change any behaviour. (On
lazy-trees, SourcePath is a <InputAccessor, CanonPath> tuple.)
Instead of constructing a markdown list in C++ (which involved all sorts
of nasty string literals), export some JSON and assemble it with the
manual build system.
Besides following the precedent set with other dumped data, this is a
better separate of content and presentation; if we decide for example we
want to display this information in a different way, or in a different
section of the manual, it will become much easier to do so.
switch statements must now match all enum values or disable the
warning.
Explicit is good. This has helped us find two bugs, after solving
another one by debugging.
From now on, adding to an enum will raise errors where they are
not explicitly handled, which is good for productivity, and helps
us decide the correct behavior in all usages.
Notably still excluded from this though are the cases where the
warning is disabled by local pragmas.
fromTOML.cc did not build despite a top-level pragma, so I've had
to resort to a makefile solution for that.
Prior to this, there was an ad-hoc whitelist in `main.cc`. Now, every
command states its stability.
In a future PR, we will adjust the manual to take advantage of this new
information in the JSON.
(It will be easier to do that once we have some experimental feature
docs to link too; see #5930 and #7798.)
The code is not local-store-specific, so we should share it with all
stores. More uniform behavior is better, and a less store-specific
functionality is more maintainable.
This fixes a FIXME added in f73d911628 by @edolstra himself.
Documentation on "classic" commands with many sub-commands are
notoriously hard to discover due to lack of overview and anchor links.
Additionally the information on common options and environment variables
is not accessible offline in man pages, and therefore often overlooked
by readers.
With this change, each sub-command of nix-store and nix-env gets its
own page in the manual (listed in the table of contents), and each own
man page.
Also, man pages for each subcommand now (again) list common options
and environment variables. While this makes each page quite long and
some common parameters don't apply, this should still make it easier
to navigate as that additional information was not accessible on the
command line at all.
It is now possible to run 'nix-store --<subcommand> --help` to display
help pages for the given subcommand.
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
This fixes the issue that `nix-build`, without experimental feature
'nix-command' enabled, recommends the experimental CLI `nix log` to view
build logs. Now it'll recommend the stable `nix-store -l` CLI instead.
Fixes https://github.com/NixOS/nix/issues/8118
See the note in the test.
We don't want these flags showing up for commands where they are
irrelevant.
Eventually, this needs a proper fix, but it need not be a blocker for
stabilize: for a quick-n-dirty punt, just put these flags behind the
`nix-command` unstable feature.
This is fine because they are only relevant for commands which we don't
need to stabilize for a while.
`legacyPackages` of nixpkgs trigger eval errors in `hasContent`, causing
the whole `legacyPackages` being skipped. We should treat it as
has-content in that case.
Instead of having a bunch of optional fields, have a few subclasses
which can have mandatory fields.
Additionally, the new `getExtraPathInfo`, and `nixpkgsFlakeRef`, are
moved to `InstallableValue`.
I did these things because https://github.com/NixOS/rfcs/pull/134 ; with
these things moved to `InstallableValue`, the base `Installable` no
longer depends on libexpr! This is a major step towards that.
Also, add a bunch of doc comments for sake of the internal API docs.
Otherwise, a trace consisting of
frame
frame
frame
non-frame
... would reach the non-frame and print the suggestion, even though
it would have ignored the non-frame anyway.
This resulted in a peculariar situation where --show-trace would have
no apparent effect, as the trace was actually already complete.
Pause logger before starting SSH connections, and resume it after the
connection is established, so that SSH password prompts are not erased
by the logger's updates.
Otherwise, when running as root and user namespaces are enabled,
opening the slave fails with EPERM.
Fixes "opening pseudoterminal slave: Permission denied" followed by a
hang (https://hydra.nixos.org/build/213104244), and "error: getting
sandbox mount namespace: No such file or directory" (#8072), which
happens when the child fails very quickly and consequently reading
/proc/<child>/ns fails.
If we conditionally "declare" the argument, as we did before, based upon
weather the feature is enabled, commands like
nix --experimental-features=foo ... --thing-gated-on-foo
won't work, because the experimental feature isn't enabled until *after*
we start parsing.
Instead, allow arguments to also be associated with experimental
features (just as we did for builtins and settings), and then the
command line parser will filter out the experimental ones.
Since the effects of arguments (handler functions) are performed right
away, we get the required behavior: earlier arguments can enable later
arguments enabled!
There is just one catch: we want to keep non-positional
flags...non-positional. So if
nix --experimental-features=foo ... --thing-gated-on-foo
works, then
nix --thing-gated-on-foo --experimental-features=foo ...
should also work.
This is not my favorite long-term solution, but for now this is
implemented by delaying the requirement of needed experimental features
until *after* all the arguments have been parsed.
We hide them in various ways if the experimental feature isn't enabled.
To do this, we had to move the experimental features list out of
libnixstore, because the setting machinary itself depends on it. To do
that, we made a new `ExperimentalFeatureSettings`.
This provides a platform-independent way to configure the SSL
certificates file in the Nix daemon. Previously we provided
instructions for overriding the environment variable in launchd, but
that obviously doesn't work with systemd. Now we can just tell users
to add
ssl-cert-file = /etc/ssl/my-certificate-bundle.crt
to their nix.conf.
These methods would previously fail on the other `Installable`s, so
moving them to this class is more correct as to where they actually
work.
Additionally, a `InstallableValueCommand` is created to make it easier
(or rather no worse than before) to write commands that just work on
`InstallableValue`s.
Besides being a cleanup to avoid failing default methods, this gets us
closer to https://github.com/NixOS/rfcs/pull/134.
Already, we had classes like `BuiltPathsCommand` and `StorePathsCommand`
which provided alternative `run` virtual functions providing the
implementation with more arguments. This was a very nice and easy way to
make writing command; just fill in the virtual functions and it is
fairly clear what to do.
However, exception to this pattern were `Installable{,s}Command`. These
two classes instead just had a field where the installables would be
stored, and various side-effecting `prepare` and `load` machinery too
fill them in. Command would wish out those fields.
This isn't so clear to use.
What this commit does is make those command classes like the others,
with richer `run` functions.
Not only does this restore the pattern making commands easier to write,
it has a number of other benefits:
- `prepare` and `load` are gone entirely! One command just hands just
hands off to the next.
- `useDefaultInstallables` because `defaultInstallables`. This takes
over `prepare` for the one case that needs it, and provides enough
flexiblity to handle `nix repl`'s idiosyncratic migration.
- We can use `ref` instead of `std::shared_ptr`. The former must be
initialized (so it is like Rust's `Box` rather than `Option<Box>`,
This expresses the invariant that the installable are in fact
initialized much better.
This is possible because since we just have local variables not
fields, we can stop worrying about the not-yet-initialized case.
- Fewer lines of code! (Finally I have a large refactor that makes the
number go down not up...)
- `nix repl` is now implemented in a clearer way.
The last item deserves further mention. `nix repl` is not like the other
installable commands because instead working from once-loaded
installables, it needs to be able to load them again and again.
To properly support this, we make a new superclass
`RawInstallablesCommand`. This class has the argument parsing and
completion logic, but does *not* hand off parsed installables but
instead just the raw string arguments.
This is exactly what `nix repl` needs, and allows us to instead of
having the logic awkwardly split between `prepare`,
`useDefaultInstallables,` and `load`, have everything right next to each
other. I think this will enable future simplifications of that argument
defaulting logic, but I am saving those for a future PR --- best to keep
code motion and more complicated boolean expression rewriting separate
steps.
The "diagnostic ignored `-Woverloaded-virtual`" pragma helps because C++
doesn't like our many `run` methods. In our case, we don't mind the
shadowing it all --- it is *intentional* that the derived class only
provides a `run` method, and doesn't call any of the overridden `run`
methods.
Helps with https://github.com/NixOS/rfcs/pull/134
Add the --base64 and --sri flags for the Base64 and SRI format output.
Add the --base16 flag to explicitly specify the hexadecimal format.
Add the --to-base64 and --to-sri flag to convert a hash to the above
mentioned format.
Hopefully this fixes "unexpected EOF" failures on macOS
(#3137, #3605, #7242, #7702).
The problem appears to be that under some circumstances, macOS
discards the output written to the slave side of the
pseudoterminal. Hence the parent never sees the "sandbox initialized"
message from the child, even though it succeeded. The conditions are:
* The child finishes very quickly. That's why this bug is likely to
trigger in nix-env tests, since that uses a builtin builder. Adding
a short sleep before the child exits makes the problem go away.
* The parent has closed its duplicate of the slave file
descriptor. This shouldn't matter, since the child has a duplicate
as well, but it does. E.g. moving the close to the bottom of
startBuilder() makes the problem go away. However, that's not a
solution because it would make Nix hang if the child dies before
sending the "sandbox initialized" message.
* The system is under high load. E.g. "make installcheck -j16" makes
the issue pretty reproducible, while it's very rare under "make
installcheck -j1".
As a fix/workaround, we now open the pseudoterminal slave in the
child, rather than the parent. This removes the second condition
(i.e. the parent no longer needs to close the slave fd) and I haven't
been able to reproduce the "unexpected EOF" with this.
This allows having multiple separate lockfiles for a single
project, which can be useful for testing against different versions of
nixpkgs; it also allows tracking custom input overrides for remote
flakes without requiring local clones of these flakes.
For example, if I want to build Nix against my locally pinned nixpkgs,
and have a lock file tracking this override independently of future
updates to said nixpkgs:
nix flake lock --output-lock-file /tmp/nix-flake.lock --override-input nixpkgs flake:nixpkgs
nix build --reference-lock-file /tmp/nix-flake.lock
Co-Authored-By: Will Fancher <elvishjerricco@gmail.com>
I saw this random failure in https://hydra.nixos.org/build/211811692:
error: opening /proc/15307/fd: No such process
while running nix-collect-garbage in a readfile-context.sh. This is
because we're not handling ESRCH errors reading /proc/<pid>/fd. So
just move the read inside the try/catch where we do handle it.
`nix copy` operations did not show progress. This is quite confusing.
Add a `progressSink` which displays the progress during `copyPaths`,
pretty much copied from `copyStorePath`.
Fixes https://github.com/NixOS/nix/issues/8000
This was causing random failures in tests/ca/substitute.ca: 'nix copy
--file ./content-addressed.nix' wouldn't get the default installable
'.' applied in InstallablesCommand::load(), so it would do nothing.
The curl download can outlive DrvOutputSubstitutionGoal (if some other
error occurs), so at shutdown setting the promise to an exception will
fail because 'this' is no longer valid in the callback. This can
manifest itself as a segfault, "corrupted double-linked list" or hang.
the term was hard to discover, as its definition and explanation were in
a very long document lacking an overview section.
search did not help because it occurs so often.
- clarify wording in the definition
- add an overview of installable types
- add "installable" to glossary
- link to definition from occurrences of the term
- be more precise about where store derivation outputs are processed
- installable Nix expressions must evaluate to a derivation
Co-authored-by: Adam Joseph <54836058+amjoseph-nixpkgs@users.noreply.github.com>
Presently when nix says something like:
```
these 486 paths will be fetched (511.54 MiB download, 6458.64 MiB unpacked):
...path1
...path2
...path3
...
...
...path486
```
It sorts path1, path2, path3, ..., path486 in lexicographic order of the
store path.
After this commit, nix will show path1, path2, path3, ..., path486 sorted by
StorePath name() (basically everything after the hash) rather than the store path.
This makes it easier to review what exactly is being downloaded at a glance,
especially when many paths need to be fetched.
We make sure the env var paths are actually set (ie. not "") before
sending them to the canonicalization function. If we forget to do so,
the user will end up facing a puzzled failed assertion internal error.
We issue a non-failing warning as a stop-gap measure. We could want to
revisit this to issue a detailed failing error message in the future.
Currently the valid key is only present when the path is invalid, which
makes checking path validity more complex than it should be. With this
change, the valid key can always be used to check if a path is valid
The release notes document the change in behavior, I don't include it
here so there is no risk to it getting out of sync.
> Motivation
>> Plumbing CLI should be simple
Store derivation installations are intended as "plumbing": very simple
utilities for advanced users and scripts, and not what regular users
interact with. (Similarly, regular Git users will use branch and tag
names not explicit hashes for most things.)
The plumbing CLI should prize simplicity over convenience; that is its
raison d'etre. If the user provides a path, we should treat it the same
way not caring what sort of path it is.
>> Scripting
This is especially important for the scripting use-case. when arbitrary
paths are sent to e.g. `nix copy` and the script author wants consistent
behavior regardless of what those store paths are. Otherwise the script
author needs to be careful to filter out `.drv` ones, and then run `nix
copy` again with those paths and `--derivation`. That is not good!
>> Surprisingly low impact
Only two lines in the tests need changing, showing that the impact of
this is pretty light.
Many command, like `nix log` will continue to work with just the
derivation passed as before. This because we used to:
- Special case the drv path and replace it with it's outputs (what this
gets rid of).
- Turn those output path *back* into the original drv path.
Now we just skip that entire round trip!
> Context
Issue #7261 lays out a broader vision for getting rid of `--derivation`,
and has this as one of its dependencies. But we can do this with or
without that.
`Installable::toDerivations` is changed to handle the case of a
`DerivedPath::Opaque` ending in `.drv`, which is new: it simply doesn't
need to do any extra work in that case. On this basis, commands like
`nix {show-derivation,log} /nix/store/...-foo.drv` still work as before,
as described above.
When testing older daemons, the post-build-hook will be run against the
old CLI, so we need the old version of the post-build-hook to support
that use-case.
Co-authored-by: Travis A. Everett <travis.a.everett@gmail.com>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
Resolves#7437 for new `nix` commands only by adding a `--stdin` flag.
If paths are also passed on the cli they will be combined with the ones
from standard input.
Whenever a file conflict happens during "nix profile install" an error
is shown that was previously thrown inside builtins.buildEnv.
We catch BuildProfileConflictError here so that we can provide the user
with more useful instructions on what to do next.
Most notably, we give the user concrete commands to use with all
parameters already filled in. This avoids the need for the user to look
up these commands in manual pages.
At the moment an Error is thrown that only holds an error message
regarding `nix-env` and `nix profile`. These tools make use of
builtins.buildEnv, but buildEnv is also used in other places. These
places are unrelated to Nix profiles, so the error shouldn't mention
these tools.
This generic error is now BuildEnvFileConflictError, which holds more
contextual information about the files that were conflicting while
building the environment.
It would be incorrect to say that the `sourceInfo` has an `outPath`
that isn't the root. `sourceInfo` is about the root, whereas only
the flake may not be about the root. Thanks Eelco for pointing that
out.
It is independent of SourceExprCommand, which is about parsing
installables, except for the fact that parsing installables is one of
the many things influenced by read-only mode.
If this documentation is inaccurate in any way please do not hesitate to suggest corrections.
My understanding of this function is strictly from reading the source code and some limited experience implementing fetchers.
