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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
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Ericson2314 committed May 12, 2023
1 parent c4aa186 commit 401d471
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Showing 4 changed files with 65 additions and 12 deletions.
20 changes: 20 additions & 0 deletions src/libcmd/installable-attr-path.cc
Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,26 @@ DerivedPathsWithInfo InstallableAttrPath::toDerivedPaths()
{
auto v = toValue(*state).first;

if (v->type() == nPath) {
auto storePath = v->path().fetchToStore(state->store);
return {{
.path = DerivedPath::Opaque {
.path = std::move(storePath),
},
.info = make_ref<ExtraPathInfo>(),
}};
}

else if (v->type() == nString) {
return {{
.path = state->coerceToDerivedPath(
noPos,
*v,
""),
.info = make_ref<ExtraPathInfo>(),
}};
}

Bindings & autoArgs = *cmd.getAutoArgs(*state);

DrvInfos drvInfos;
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19 changes: 7 additions & 12 deletions src/libcmd/installable-flake.cc
Original file line number Diff line number Diff line change
Expand Up @@ -106,18 +106,13 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
}

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);
return {{
.path = state->coerceToDerivedPath(
noPos,
v,
fmt("while evaluating the flake output attribute '%s'", attrPath)),
.info = make_ref<ExtraPathInfo>(),
}};
}

else
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15 changes: 15 additions & 0 deletions tests/build.sh
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,21 @@ nix build -f multiple-outputs.nix --json 'e^*' --no-link | jq --exit-status '
(.outputs | keys == ["a_a", "b", "c"]))
'

# test buidling from non-drv attr path

nix build -f multiple-outputs.nix --json 'e.a_a.outPath' --no-link | jq --exit-status '
(.[0] |
(.drvPath | match(".*multiple-outputs-e.drv")) and
(.outputs | keys == ["a_a"]))
'

# Illegal type of string context
expect 1 nix build -f multiple-outputs.nix --json 'e.a_a.drvPath' --no-link

nix build --impure --json --expr 'builtins.unsafeDiscardOutputDependency (import ./multiple-outputs.nix).e.a_a.drvPath' --no-link | jq --exit-status '
(.[0] | .path | match(".*multiple-outputs-e.drv"))
'

# Test building from raw store path to drv not expression.

drv=$(nix eval -f multiple-outputs.nix --raw a.drvPath)
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23 changes: 23 additions & 0 deletions tests/flakes/build-paths.sh
Original file line number Diff line number Diff line change
Expand Up @@ -41,10 +41,25 @@ cat > $flake1Dir/flake.nix <<EOF
a8 = builtins.storePath $dep;
a9 = "$dep";
drvCall = with import ./config.nix; mkDerivation {
name = "simple";
builder = ./simple.builder.sh;
PATH = "";
goodPath = path;
};
a10 = builtins.unsafeDiscardOutputDependency self.drvCall.drvPath;
a11 = self.drvCall.drvPath;
a12 = self.drvCall.outPath;
};
}
EOF

cp ../simple.nix ../simple.builder.sh ../config.nix $flake1Dir/

echo bar > $flake1Dir/foo

nix build --json --out-link $TEST_ROOT/result $flake1Dir#a1
Expand All @@ -64,3 +79,11 @@ nix build --impure --json --out-link $TEST_ROOT/result $flake1Dir#a8
diff common.sh $TEST_ROOT/result

(! nix build --impure --json --out-link $TEST_ROOT/result $flake1Dir#a9)

nix build --json --out-link $TEST_ROOT/result $flake1Dir#a10
[[ $(readlink -e $TEST_ROOT/result) = *simple.drv ]]

(! nix build --json --out-link $TEST_ROOT/result $flake1Dir#a11)

nix build --json --out-link $TEST_ROOT/result $flake1Dir#a12
[[ -e $TEST_ROOT/result/hello ]]

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