forked from lix-project/lix
nix-shell: restore backwards-compat with old nixpkgs
Basically an attempt to resume fixing #5543 for a breakage introduced
earlier[1]. Basically, when evaluating an older `nixpkgs` with
`nix-shell` the following error occurs:
λ ma27 [~] → nix-shell -I nixpkgs=channel:nixos-18.03 -p nix
error: anonymous function at /nix/store/zakqwc529rb6xcj8pwixjsxscvlx9fbi-source/pkgs/top-level/default.nix:20:1 called with unexpected argument 'inNixShell'
at /nix/store/zakqwc529rb6xcj8pwixjsxscvlx9fbi-source/pkgs/top-level/impure.nix:82:1:
81|
82| import ./. (builtins.removeAttrs args [ "system" "platform" ] // {
| ^
83| inherit config overlays crossSystem;
This is a problem because one of the main selling points of Nix is that
you can evaluate any old Nix expression and still get the same result
(which also means that it *still evaluates*). In fact we're deprecating,
but not removing a lot of stuff for that reason such as unquoted URLs[2]
or `builtins.toPath`. However this property was essentially thrown away
here.
The change is rather simple: check if `inNixShell` is specified in the
formals of an auto-called function. This means that
{ inNixShell ? false }:
builtins.trace inNixShell
(with import <nixpkgs> { }; makeShell { name = "foo"; })
will show `trace: true` while
args@{ ... }:
builtins.trace args.inNixShell
(with import <nixpkgs> { }; makeShell { name = "foo"; })
will throw the following error:
error: attribute 'inNixShell' missing
This is explicitly needed because the function in
`pkgs/top-level/impure.nix` of e.g. NixOS 18.03 has an ellipsis[3], but
passes the attribute-set on to another lambda with formals that doesn't
have an ellipsis anymore (hence the error from above). This was perhaps
a mistake, but we can't fix it anymore. This also means that there's
AFAICS no proper way to check if the attr-set that's passed to the Nix
code via `EvalState::autoCallFunction` is eventually passed to a lambda
with formals where `inNixShell` is missing.
However, this fix comes with a certain price. Essentially every
`shell.nix` that assumes `inNixShell` to be passed to the formals even
without explicitly specifying it would break with this[4]. However I think
that this is ugly, but preferable:
* Nix 2.3 was declared stable by NixOS up until recently (well, it still
is as long as 21.11 is alive), so most people might not have even
noticed that feature.
* We're talking about a way shorter time-span with this change being
in the wild, so the fallout should be smaller IMHO.
[1] 9d612c393a
[2] https://github.com/NixOS/rfcs/pull/45#issuecomment-488232537
[3] https://github.com/NixOS/nixpkgs/blob/release-18.03/pkgs/top-level/impure.nix#L75
[4] See e.g. the second expression in this commit-message or the changes
for `tests/ca/nix-shell.sh`.
This commit is contained in:
parent
03226aa053
commit
98946e2d9c
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@ -257,11 +257,12 @@ static void main_nix_build(int argc, char * * argv)
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auto autoArgs = myArgs.getAutoArgs(*state);
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auto autoArgsWithInNixShell = autoArgs;
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if (runEnv) {
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auto newArgs = state->buildBindings(autoArgs->size() + 1);
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auto newArgs = state->buildBindings(autoArgsWithInNixShell->size() + 1);
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newArgs.alloc("inNixShell").mkBool(true);
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for (auto & i : *autoArgs) newArgs.insert(i);
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autoArgs = newArgs.finish();
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autoArgsWithInNixShell = newArgs.finish();
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}
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if (packages) {
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@ -316,10 +317,39 @@ static void main_nix_build(int argc, char * * argv)
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Value vRoot;
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state->eval(e, vRoot);
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std::function<bool(const Value & v)> takesNixShellAttr;
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takesNixShellAttr = [&](const Value & v) {
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if (!runEnv) {
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return false;
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}
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bool add = false;
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if (v.type() == nFunction && v.lambda.fun->hasFormals()) {
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for (auto & i : v.lambda.fun->formals->formals) {
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if (state->symbols[i.name] == "inNixShell") {
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add = true;
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break;
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}
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}
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}
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return add;
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};
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for (auto & i : attrPaths) {
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Value & v(*findAlongAttrPath(*state, i, *autoArgs, vRoot).first);
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Value & v(*findAlongAttrPath(
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*state,
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i,
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takesNixShellAttr(vRoot) ? *autoArgsWithInNixShell : *autoArgs,
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vRoot
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).first);
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state->forceValue(v, [&]() { return v.determinePos(noPos); });
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getDerivations(*state, v, "", *autoArgs, drvs, false);
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getDerivations(
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*state,
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v,
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"",
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takesNixShellAttr(v) ? *autoArgsWithInNixShell : *autoArgs,
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drvs,
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false
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);
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}
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}
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@ -1 +1 @@
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{ ... }@args: import ./shell.nix (args // { contentAddressed = true; })
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{ inNixShell ? false, ... }@args: import ./shell.nix (args // { contentAddressed = true; })
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@ -102,3 +102,10 @@ source <(nix print-dev-env -f "$shellDotNix" shellDrv)
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[[ ${arr2[1]} = $'\n' ]]
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[[ ${arr2[2]} = $'x\ny' ]]
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[[ $(fun) = blabla ]]
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# Test nix-shell with ellipsis and no `inNixShell` argument (for backwards compat with old nixpkgs)
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cat >$TEST_ROOT/shell-ellipsis.nix <<EOF
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{ system ? "x86_64-linux", ... }:
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(import $shellDotNix { }).shellDrv
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EOF
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nix-shell $TEST_ROOT/shell-ellipsis.nix --run "true"
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