Allow hard links between the outputs of a derivation

src/libstore/build.cc

@@ -844,6 +844,11 @@ private:
     bool repair;
     map<Path, Path> redirectedBadOutputs;
 
+    /* Set of inodes seen during calls to canonicalisePathMetaData()
+       for this build's outputs.  This needs to be shared between
+       outputs to allow hard links between outputs. */
+    InodesSeen inodesSeen;
+
     /* Magic exit code denoting that setting up the child environment
        failed.  (It's possible that the child actually returns the
        exit code, but ah well.) */
@@ -1493,7 +1498,7 @@ void DerivationGoal::buildDone()
                 /* Canonicalise first.  This ensures that the path
                    we're rewriting doesn't contain a hard link to
                    /etc/shadow or something like that. */
-                canonicalisePathMetaData(path, buildUser.enabled() ? buildUser.getUID() : -1);
+                canonicalisePathMetaData(path, buildUser.enabled() ? buildUser.getUID() : -1, inodesSeen);
 
                 /* FIXME: this is in-memory. */
                 StringSink sink;
@@ -2307,7 +2312,7 @@ void DerivationGoal::computeClosure()
         /* Get rid of all weird permissions.  This also checks that
            all files are owned by the build user, if applicable. */
         canonicalisePathMetaData(path,
-            buildUser.enabled() && rewrittenPaths.find(path) == rewrittenPaths.end() ? buildUser.getUID() : -1);
+            buildUser.enabled() && rewrittenPaths.find(path) == rewrittenPaths.end() ? buildUser.getUID() : -1, inodesSeen);
 
         /* For this output path, find the references to other paths
            contained in it.  Compute the SHA-256 NAR hash at the same

src/libstore/local-store.cc

@@ -500,10 +500,6 @@ void canonicaliseTimestampAndPermissions(const Path & path)
 }
 
 
-typedef std::pair<dev_t, ino_t> Inode;
-typedef set<Inode> InodesSeen;
-
-
 static void canonicalisePathMetaData_(const Path & path, uid_t fromUid, InodesSeen & inodesSeen)
 {
     checkInterrupt();
@@ -561,10 +557,8 @@ static void canonicalisePathMetaData_(const Path & path, uid_t fromUid, InodesSe
 }
 
 
-void canonicalisePathMetaData(const Path & path, uid_t fromUid)
+void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & inodesSeen)
 {
-    InodesSeen inodesSeen;
-
     canonicalisePathMetaData_(path, fromUid, inodesSeen);
 
     /* On platforms that don't have lchown(), the top-level path can't
@@ -580,6 +574,13 @@ void canonicalisePathMetaData(const Path & path, uid_t fromUid)
 }
 
 
+void canonicalisePathMetaData(const Path & path, uid_t fromUid)
+{
+    InodesSeen inodesSeen;
+    canonicalisePathMetaData(path, fromUid, inodesSeen);
+}
+
+
 void LocalStore::checkDerivationOutputs(const Path & drvPath, const Derivation & drv)
 {
     string drvName = storePathToName(drvPath);

src/libstore/local-store.hh

@@ -305,6 +305,10 @@ private:
 };
 
 
+typedef std::pair<dev_t, ino_t> Inode;
+typedef set<Inode> InodesSeen;
+
+
 /* "Fix", or canonicalise, the meta-data of the files in a store path
    after it has been built.  In particular:
    - the last modification date on each file is set to 1 (i.e.,
@@ -313,6 +317,7 @@ private:
      without execute permission; setuid bits etc. are cleared)
    - the owner and group are set to the Nix user and group, if we're
      in a setuid Nix installation. */
+void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & inodesSeen);
 void canonicalisePathMetaData(const Path & path, uid_t fromUid);
 
 void canonicaliseTimestampAndPermissions(const Path & path);