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libcmd/installables: force re-evaluation of cached failures

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I think that it's not very helpful to get "cached failures" in a wrong
`flake.nix`. This can be very confusing when debugging a Nix expression.
See for instance NixOS/nixpkgs#118115.

In fact, the eval cache allows a forced reevaluation which is used for
e.g. `nix eval`.

This change makes sure that this is the case for `nix build` as well. So
rather than

    λ ma27 [~/Projects/exp] → ../nix/outputs/out/bin/nix build -L --rebuild --experimental-features 'nix-command flakes'
    error: cached failure of attribute 'defaultPackage.x86_64-linux'

the evaluation of already-evaluated (and failed) attributes looks like
this now:

    λ ma27 [~/Projects/exp] → ../nix/outputs/out/bin/nix build -L --rebuild --experimental-features 'nix-command flakes'
    error: attribute 'hell' missing

           at /nix/store/mrnvi9ss8zn5wj6gpn4bcd68vbh42mfh-source/flake.nix:6:35:

                5|
                6|     packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hell;
                 |                                   ^
                7|
    (use '--show-trace' to show detailed location information)
This commit is contained in:
Maximilian Bosch 2021-04-03 12:04:57 +02:00
parent 76980a1f3d
commit 6905291daf
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GPG key ID: 091DBF4D1FC46B8E
3 changed files with 8 additions and 4 deletions
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6
src/libcmd/installables.cc
View file

@ -503,7 +503,11 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
auto root = cache->getRoot();
for (auto & attrPath : getActualAttrPaths()) {
auto attr = root->findAlongAttrPath(parseAttrPath(*state, attrPath));
auto attr = root->findAlongAttrPath(
parseAttrPath(*state, attrPath),
true
);
if (!attr) continue;
if (!attr->isDerivation())

4
src/libexpr/eval-cache.cc
View file

@ -486,11 +486,11 @@ std::shared_ptr<AttrCursor> AttrCursor::getAttr(std::string_view name)
return getAttr(root->state.symbols.create(name));
}
std::shared_ptr<AttrCursor> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath)
std::shared_ptr<AttrCursor> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force)
{
auto res = shared_from_this();
for (auto & attr : attrPath) {
res = res->maybeGetAttr(attr);
res = res->maybeGetAttr(attr, force);
if (!res) return {};
}
return res;

2
src/libexpr/eval-cache.hh
View file

@ -102,7 +102,7 @@ public:
std::shared_ptr<AttrCursor> getAttr(std::string_view name);
std::shared_ptr<AttrCursor> findAlongAttrPath(const std::vector<Symbol> & attrPath);
std::shared_ptr<AttrCursor> findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force = false);
std::string getString();