Allow substitutes for builds that have preferLocalBuild set

Not substituting builds with "preferLocalBuild = true" was a bad idea,
because it didn't take the cost of dependencies into account. For
instance, if we can't substitute a fetchgit call, then we have to
download/build git and all its dependencies.

Partially reverts 5558652709f27e8a887580b77b93c705659d7a4b and adds a
new derivation attribute "allowSubstitutes" to specify whether a
derivation may be substituted.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 2facda815..736434ca4 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -120,7 +120,7 @@ void queryMissing(StoreAPI & store, const PathSet & targets,
                 if (invalid.empty()) continue;
 
                 todoDrv.insert(*i);
-                if (settings.useSubstitutes && !willBuildLocally(drv))
+                if (settings.useSubstitutes && substitutesAllowed(drv))
                     query.insert(invalid.begin(), invalid.end());
             }
 
@@ -144,7 +144,7 @@ void queryMissing(StoreAPI & store, const PathSet & targets,
 
             PathSet outputs;
             bool mustBuild = false;
-            if (settings.useSubstitutes && !willBuildLocally(drv)) {
+            if (settings.useSubstitutes && substitutesAllowed(drv)) {
                 foreach (DerivationOutputs::iterator, j, drv.outputs) {
                     if (!wantOutput(j->first, i2.second)) continue;
                     if (!store.isValidPath(j->second.path)) {