Merge pull request #7601 from obsidiansystems/string-installables

Make more string values work as installables

4 files changed, 55 insertions, 25 deletions

diff --git a/src/libcmd/installable-attr-path.cc b/src/libcmd/installable-attr-path.cc
index cf513126d..b35ca2910 100644
--- a/src/libcmd/installable-attr-path.cc
+++ b/src/libcmd/installable-attr-path.cc
@@ -46,7 +46,15 @@ std::pair<Value *, PosIdx> InstallableAttrPath::toValue(EvalState & state)
 
 DerivedPathsWithInfo InstallableAttrPath::toDerivedPaths()
 {
-    auto v = toValue(*state).first;
+    auto [v, pos] = toValue(*state);
+
+    if (std::optional derivedPathWithInfo = trySinglePathToDerivedPaths(
+        *v,
+        pos,
+        fmt("while evaluating the attribute '%s'", attrPath)))
+    {
+        return { *derivedPathWithInfo };
+    }
 
     Bindings & autoArgs = *cmd.getAutoArgs(*state);
 
diff --git a/src/libcmd/installable-flake.cc b/src/libcmd/installable-flake.cc
index 37e59cfdf..eb944240b 100644
--- a/src/libcmd/installable-flake.cc
+++ b/src/libcmd/installable-flake.cc
@@ -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>(),
-            }};
-        }
-
-        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);
+        if (std::optional derivedPathWithInfo = trySinglePathToDerivedPaths(
+            v,
+            noPos,
+            fmt("while evaluating the flake output attribute '%s'", attrPath)))
+        {
+            return { *derivedPathWithInfo };
         }
-
         else
             throw Error("flake output attribute '%s' is not a derivation or path", attrPath);
     }
diff --git a/src/libcmd/installable-value.cc b/src/libcmd/installable-value.cc
index 3a7ede4e2..1eff293cc 100644
--- a/src/libcmd/installable-value.cc
+++ b/src/libcmd/installable-value.cc
@@ -41,4 +41,26 @@ ref<InstallableValue> InstallableValue::require(ref<Installable> installable)
     return ref { castedInstallable };
 }
 
+std::optional<DerivedPathWithInfo> InstallableValue::trySinglePathToDerivedPaths(Value & v, const PosIdx pos, std::string_view errorCtx)
+{
+    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(pos, v, errorCtx),
+            .info = make_ref<ExtraPathInfo>(),
+        }};
+    }
+
+    else return std::nullopt;
+}
+
 }
diff --git a/src/libcmd/installable-value.hh b/src/libcmd/installable-value.hh
index 5ab7eee16..3138ce8ec 100644
--- a/src/libcmd/installable-value.hh
+++ b/src/libcmd/installable-value.hh
@@ -98,6 +98,24 @@ struct InstallableValue : Installable
 
     static InstallableValue & require(Installable & installable);
     static ref<InstallableValue> require(ref<Installable> installable);
+
+protected:
+
+    /**
+     * Handles either a plain path, or a string with a single string
+     * context elem in the right format. The latter case is handled by
+     * `EvalState::coerceToDerivedPath()`; see it for details.
+     *
+     * @param v Value that is hopefully a string or path per the above.
+     *
+     * @param pos Position of value to aid with diagnostics.
+     *
+     * @param errorCtx Arbitrary message for use in potential error message when something is wrong with `v`.
+     *
+     * @result A derived path (with empty info, for now) if the value
+     * matched the above criteria.
+     */
+    std::optional<DerivedPathWithInfo> trySinglePathToDerivedPaths(Value & v, const PosIdx pos, std::string_view errorCtx);
 };
 
 }