* Support for fixed-output hashes over directory trees (i.e., over the

NAR dump of the path).

scripts/nix-prefetch-url.in

@@ -25,7 +25,7 @@ if test -z "$hash"; then
         tmpPath1=/tmp/nix-prefetch-url-$$ # !!! security?
     fi
 
-    # Perform the checkout.
+    # Perform the download.
     @curl@ --fail --location --max-redirs 20 "$url" > $tmpPath1
 
     # Compute the hash.
@@ -47,7 +47,7 @@ storeExpr=$( \
     | @bindir@/nix-instantiate -)
 
 # Realise it.
-finalPath=$(@bindir@/nix-store -q --force-realise $storeExpr)
+finalPath=$(@bindir@/nix-store -r $storeExpr)
     
 if ! test -n "$QUIET"; then echo "path is $finalPath" >&2; fi
 

src/libexpr/primops.cc

@@ -194,6 +194,7 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
     
     string outputHash;
     string outputHashAlgo;
+    bool outputHashRecursive = false;
 
     for (ATermIterator i(attrs.keys()); i; ++i) {
         string key = aterm2String(*i);
@@ -228,6 +229,11 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
             else if (key == "name") drvName = s;
             else if (key == "outputHash") outputHash = s;
             else if (key == "outputHashAlgo") outputHashAlgo = s;
+            else if (key == "outputHashMode") {
+                if (s == "recursive") outputHashRecursive = true; 
+                else if (s == "flat") outputHashRecursive = false;
+                else throw Error(format("invalid value `%1%' for `outputHashMode' attribute") % s);
+            }
         }
     }
     
@@ -255,6 +261,7 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
             h = parseHash32(ht, outputHash);
         string s = outputHash;
         outputHash = printHash(h);
+        if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
     }
 
     /* Check the derivation name.  It shouldn't contain whitespace,

src/libstore/build.cc

@@ -1082,17 +1082,17 @@ void DerivationGoal::computeClosure()
            outputs (i.e., the content hash should match the specified
            hash). */ 
         if (i->second.hash != "") {
-            HashType ht = parseHashType(i->second.hashAlgo);
-            if (ht == htUnknown)
-                throw Error(format("unknown hash algorithm `%1%'") % i->second.hashAlgo);
-            Hash h = parseHash(ht, i->second.hash);
-            Hash h2 = hashFile(ht, path);
-            if (h != h2)
-                throw Error(
-                    format("output path `%1% should have %2% hash `%3%', instead has `%4%'")
-                    % path % i->second.hashAlgo % printHash(h) % printHash(h2));
 
-            /* Also, the output path should be a regular file withouth
+            bool recursive = false;
+            string algo = i->second.hashAlgo;
+            
+            if (string(algo, 0, 2) == "r:") {
+                recursive = true;
+                algo = string(algo, 2);
+            }
+
+            if (!recursive) {
+                /* The output path should be a regular file without
                    execute permission. */
                 struct stat st;
                 if (lstat(path.c_str(), &st))
@@ -1103,6 +1103,18 @@ void DerivationGoal::computeClosure()
                         % path);
             }
 
+            /* Check the hash. */
+            HashType ht = parseHashType(algo);
+            if (ht == htUnknown)
+                throw Error(format("unknown hash algorithm `%1%'") % algo);
+            Hash h = parseHash(ht, i->second.hash);
+            Hash h2 = recursive ? hashPath(ht, path) : hashFile(ht, path);
+            if (h != h2)
+                throw Error(
+                    format("output path `%1% should have %2% hash `%3%', instead has `%4%'")
+                    % path % algo % printHash(h) % printHash(h2));
+        }
+
 	canonicalisePathMetaData(path);
 
 	/* For this output path, find the references to other paths contained