Fix the detection of already built drv outputs

PRs #4370 and #4348 had a bad interaction in that the second broke the fist
one in a not trivial way.

The issue was that since #4348 the logic for detecting whether a
derivation output is already built requires some logic that was specific
to the `LocalStore`.

It happens though that most of this logic could be upstreamed to any `Store`,
which is what this commit does.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 7cdadc1f3..ce95b78b1 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -416,8 +416,13 @@ public:
     /* Query the mapping outputName => outputPath for the given derivation. All
        outputs are mentioned so ones mising the mapping are mapped to
        `std::nullopt`.  */
-    virtual std::map<std::string, std::optional<StorePath>> queryPartialDerivationOutputMap(const StorePath & path)
-    { unsupported("queryPartialDerivationOutputMap"); }
+    virtual std::map<std::string, std::optional<StorePath>> queryPartialDerivationOutputMap(const StorePath & path);
+
+    /*
+     * Similar to `queryPartialDerivationOutputMap`, but doesn't try to resolve
+     * the derivation
+     */
+    virtual std::map<std::string, std::optional<StorePath>> queryDerivationOutputMapNoResolve(const StorePath & path);
 
     /* Query the mapping outputName=>outputPath for the given derivation.
        Assume every output has a mapping and throw an exception otherwise. */