Use the fs accessor for readInvalidDerivation

Extend `FSAccessor::readFile` to allow not checking that the path is a
valid one, and rewrite `readInvalidDerivation` using this extended
`readFile`.

Several places in the code use `readInvalidDerivation`, either because
they need to read a derivation that has been written in the store but
not registered yet, or more generally to prevent a deadlock because
`readDerivation` tries to lock the state, so can't be called from a
place where the lock is already held.
However, `readInvalidDerivation` implicitely assumes that the store is a
`LocalFSStore`, which isn't always the case.

The concrete motivation for this is that it's required for `nix copy
--from someBinaryCache` to work, which is tremendously useful for the
tests.

1 files changed, 9 insertions, 12 deletions

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 7bf9235b2..25e28cffa 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1018,26 +1018,23 @@ Derivation Store::derivationFromPath(const StorePath & drvPath)
     return readDerivation(drvPath);
 }
 
-
-Derivation Store::readDerivation(const StorePath & drvPath)
+Derivation readDerivationCommon(Store& store, const StorePath& drvPath, bool requireValidPath)
 {
-    auto accessor = getFSAccessor();
+    auto accessor = store.getFSAccessor();
     try {
-        return parseDerivation(*this,
-            accessor->readFile(printStorePath(drvPath)),
+        return parseDerivation(store,
+            accessor->readFile(store.printStorePath(drvPath), requireValidPath),
             Derivation::nameFromPath(drvPath));
     } catch (FormatError & e) {
-        throw Error("error parsing derivation '%s': %s", printStorePath(drvPath), e.msg());
+        throw Error("error parsing derivation '%s': %s", store.printStorePath(drvPath), e.msg());
     }
 }
 
+Derivation Store::readDerivation(const StorePath & drvPath)
+{ return readDerivationCommon(*this, drvPath, true); }
+
 Derivation Store::readInvalidDerivation(const StorePath & drvPath)
-{
-    return parseDerivation(
-        *this,
-        readFile(Store::toRealPath(drvPath)),
-        Derivation::nameFromPath(drvPath));
-}
+{ return readDerivationCommon(*this, drvPath, false); }
 
 }