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Make more string values work as installables

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As discussed in #7417, it would be good to make more string values work
as installables. That is to say, if an installable refers to a value,
and the value is a string, it used to not work at all, since #7484, it
works somewhat, and this PR make it work some more.

The new cases that are added for `BuiltPath` contexts:

- Fixed input- or content-addressed derivation:

  ```
  nix-repl> hello.out.outPath
  "/nix/store/jppfl2bp1zhx8sgs2mgifmsx6dv16mv2-hello-2.12"

  nix-repl> :p builtins.getContext hello.out.outPath
  { "/nix/store/c7jrxqjhdda93lhbkanqfs07x2bzazbm-hello-2.12.drv" = { outputs = [ "out" ]; }; }

  The string matches the specified single output of that derivation, so
  it should also be valid.

- Floating content-addressed derivation:

  ```
  nix-repl> (hello.overrideAttrs (_: { __contentAddressed = true; })).out.outPath
  "/1a08j26xqc0zm8agps8anxpjji410yvsx4pcgyn4bfan1ddkx2g0"

  nix-repl> :p builtins.getContext (hello.overrideAttrs (_: { __contentAddressed = true; })).out.outPath
  { "/nix/store/qc645pyf9wl37c6qvqzaqkwsm1gp48al-hello-2.12.drv" = { outputs = [ "out" ]; }; }
  ```

  The string is not a path but a placeholder, however it also matches
  the context, and because it is a CA derivation we have no better
  option. This should also be valid.

We may also want to think about richer attrset based values (also
discussed in that issue and #6507), but this change "completes" our
string-based building blocks, from which the others can be desugared
into or at least described/document/taught in terms of.

Progress towards #7417

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
This commit is contained in:
John Ericson 2023-01-10 17:18:59 -05:00
parent 5a23b80b0a
commit d2162e7acd
6 changed files with 110 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

30
src/libcmd/installable-flake.cc
View file

@ -95,31 +95,13 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
// FIXME: use eval cache?
auto v = attr->forceValue();
if (v.type() == nPath) {
auto storePath = v.path().fetchToStore(state->store);
return {{
.path = DerivedPath::Opaque {
.path = std::move(storePath),
},
.info = make_ref<ExtraPathInfo>(),
}};
if (std::optional derivedPathWithInfo = trySinglePathToDerivedPaths(
v,
noPos,
fmt("while evaluating the flake output attribute '%s'", attrPath)))
{
return { *derivedPathWithInfo };
}
else if (v.type() == nString) {
NixStringContext context;
auto s = state->forceString(v, context, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
auto storePath = state->store->maybeParseStorePath(s);
if (storePath && context.count(NixStringContextElem::Opaque { .path = *storePath })) {
return {{
.path = DerivedPath::Opaque {
.path = std::move(*storePath),
},
.info = make_ref<ExtraPathInfo>(),
}};
} else
throw Error("flake output attribute '%s' evaluates to the string '%s' which is not a store path", attrPath, s);
}
else
throw Error("flake output attribute '%s' is not a derivation or path", attrPath);
}