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NixOS · Jan 27, 2023 · f57d7f4 · f57d7f4
1 parent eca5eac
commit f57d7f4
Showing 1 changed file with 6 additions and 5 deletions.
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
@@ -621,23 +621,23 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
             std::string_view s = state->forceString(v, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
             if (context.size() != 1)
                 throw Error(
-                    "flake output attribute '%s' evaluates to the string '%s' which does not denote exactly one store",
+                    "flake output attribute '%s' evaluates a string '%s' which which has multiple entries in its context. It should only have one entry",
                     attrPath, s);
             return {{
                 .path = std::visit(overloaded {
                     [&](NixStringContextElem::Opaque & o) -> DerivedPath {
                        auto sExpected = state->store->printStorePath(o.path);
                        if (s != sExpected)
                            throw Error(
-                               "flake output attribute '%s' evaluates to the string '%s' which should be '%s' but is not",
+                               "flake output attribute '%s' evaluates to the path string '%s', but its context has the different path '%s'",
                                attrPath, s, sExpected);
                        return DerivedPath::Opaque {
                            .path = std::move(o.path),
                        };
                     },
                     [&](NixStringContextElem::DrvDeep & o) -> DerivedPath {
                        throw Error(
-                           "flake output attribute '%s' evaluates to the string '%s' which unsupported String Context",
+                           "flake output attribute '%s' evaluates to the string '%s' whose context context refers to a complete source and binary closure. This is not supported at this time",
                            attrPath, s);
                     },
                     [&](NixStringContextElem::Built & o) -> DerivedPath {
@@ -646,13 +646,14 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
                        if (i == drv.outputs.end())
                            throw Error("derivation '%s' does not have output '%s'", state->store->printStorePath(o.drvPath), o.output);
                        auto optOutputPath = i->second.path(*state->store, drv.name, o.output);
+                       // This is testing for the case of CA derivations
                        auto sExpected = optOutputPath
                            ? state->store->printStorePath(*optOutputPath)
                            : downstreamPlaceholder(*state->store, o.drvPath, o.output);
                        if (s != sExpected)
                            throw Error(
-                               "flake output attribute '%s' evaluates to the string '%s' which should be '%s' but is not",
-                               attrPath, s, sExpected);
+                               "flake output attribute '%s' evaluates to a string '%s' whose context has '%s', but the string is not the right placeholder for this derivation output. It should be '%s'",
+                               attrPath, s, o.to_string(*state.store), sExpected);
                        return DerivedPath::Built {
                            .drvPath = std::move(o.drvPath),
                            .outputs = OutputsSpec::Names { std::move(o.output) },