* New primop builtins.filterSource, which can be used to filter files

from a source directory.  All files for which a predicate function
  returns true are copied to the store.  Typical example is to leave
  out the .svn directory:

    stdenv.mkDerivation {
      ...
      src = builtins.filterSource
        (path: baseNameOf (toString path) != ".svn")
        ./source-dir;
      # as opposed to
      #   src = ./source-dir;
    }

  This is important because the .svn directory influences the hash in
  a rather unpredictable and variable way.

src/libstore/build.cc

@@ -949,7 +949,7 @@ void DerivationGoal::buildDone()
                as that means that someone else can have interfered
                with the build.  Also, the output should be owned by
                the build user. */
-            if ((st.st_mode & (S_IWGRP | S_IWOTH)) ||
+            if ((!S_ISLNK(st.st_mode) && (st.st_mode & (S_IWGRP | S_IWOTH))) ||
                 (buildUser.enabled() && st.st_uid != buildUser.getUID()))
                 throw BuildError(format("suspicious ownership or permission on `%1%'; rejecting this build output") % path);
 #endif

src/libstore/local-store.cc

@@ -171,33 +171,7 @@ void createStoreTransaction(Transaction & txn)
 }
 
 
-/* Path copying. */
-
-struct CopySink : Sink
-{
-    string s;
-    virtual void operator () (const unsigned char * data, unsigned int len)
-    {
-        s.append((const char *) data, len);
-    }
-};
-
-
-struct CopySource : Source
-{
-    string & s;
-    unsigned int pos;
-    CopySource(string & _s) : s(_s), pos(0) { }
-    virtual void operator () (unsigned char * data, unsigned int len)
-    {
-        s.copy((char *) data, len, pos);
-        pos += len;
-        assert(pos <= s.size());
-    }
-};
-
-
-void copyPath(const Path & src, const Path & dst)
+void copyPath(const Path & src, const Path & dst, PathFilter & filter)
 {
     debug(format("copying `%1%' to `%2%'") % src % dst);
 
@@ -206,10 +180,10 @@ void copyPath(const Path & src, const Path & dst)
        for very large paths, but `copyPath' is mainly used for small
        files. */ 
 
-    CopySink sink;
-    dumpPath(src, sink);
+    StringSink sink;
+    dumpPath(src, sink, filter);
 
-    CopySource source(sink.s);
+    StringSource source(sink.s);
     restorePath(dst, source);
 }
 
@@ -646,13 +620,13 @@ static void invalidatePath(Transaction & txn, const Path & path)
 
 
 Path LocalStore::addToStore(const Path & _srcPath, bool fixed,
-    bool recursive, string hashAlgo)
+    bool recursive, string hashAlgo, PathFilter & filter)
 {
     Path srcPath(absPath(_srcPath));
     debug(format("adding `%1%' to the store") % srcPath);
 
     std::pair<Path, Hash> pr =
-        computeStorePathForPath(srcPath, fixed, recursive, hashAlgo);
+        computeStorePathForPath(srcPath, fixed, recursive, hashAlgo, filter);
     Path & dstPath(pr.first);
     Hash & h(pr.second);
 
@@ -669,9 +643,9 @@ Path LocalStore::addToStore(const Path & _srcPath, bool fixed,
 
             if (pathExists(dstPath)) deletePathWrapped(dstPath);
 
-            copyPath(srcPath, dstPath);
+            copyPath(srcPath, dstPath, filter);
 
-            Hash h2 = hashPath(htSHA256, dstPath);
+            Hash h2 = hashPath(htSHA256, dstPath, filter);
             if (h != h2)
                 throw Error(format("contents of `%1%' changed while copying it to `%2%' (%3% -> %4%)")
                     % srcPath % dstPath % printHash(h) % printHash(h2));

src/libstore/local-store.hh

@@ -50,7 +50,8 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path addToStore(const Path & srcPath, bool fixed = false,
-        bool recursive = false, string hashAlgo = "");
+        bool recursive = false, string hashAlgo = "",
+        PathFilter & filter = defaultPathFilter);
 
     Path addTextToStore(const string & suffix, const string & s,
         const PathSet & references);

src/libstore/remote-store.cc

@@ -213,7 +213,7 @@ void RemoteStore::queryReferrers(const Path & path,
 
 
 Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
-    bool recursive, string hashAlgo)
+    bool recursive, string hashAlgo, PathFilter & filter)
 {
     Path srcPath(absPath(_srcPath));
     
@@ -222,7 +222,7 @@ Path RemoteStore::addToStore(const Path & _srcPath, bool fixed,
     writeInt(fixed ? 1 : 0, to);
     writeInt(recursive ? 1 : 0, to);
     writeString(hashAlgo, to);
-    dumpPath(srcPath, to);
+    dumpPath(srcPath, to, filter);
     processStderr();
     Path path = readStorePath(from);
     return path;

src/libstore/remote-store.hh

@@ -38,7 +38,8 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path addToStore(const Path & srcPath, bool fixed = false,
-        bool recursive = false, string hashAlgo = "");
+        bool recursive = false, string hashAlgo = "",
+        PathFilter & filter = defaultPathFilter);
 
     Path addTextToStore(const string & suffix, const string & s,
         const PathSet & references);

src/libstore/store-api.cc

@@ -94,9 +94,9 @@ Path makeFixedOutputPath(bool recursive,
 
 
 std::pair<Path, Hash> computeStorePathForPath(const Path & srcPath,
-    bool fixed, bool recursive, string hashAlgo)
+    bool fixed, bool recursive, string hashAlgo, PathFilter & filter)
 {
-    Hash h = hashPath(htSHA256, srcPath);
+    Hash h = hashPath(htSHA256, srcPath, filter);
 
     string baseName = baseNameOf(srcPath);
 
@@ -104,7 +104,7 @@ std::pair<Path, Hash> computeStorePathForPath(const Path & srcPath,
     
     if (fixed) {
         HashType ht(parseHashType(hashAlgo));
-        Hash h2 = recursive ? hashPath(ht, srcPath) : hashFile(ht, srcPath);
+        Hash h2 = recursive ? hashPath(ht, srcPath, filter) : hashFile(ht, srcPath);
         dstPath = makeFixedOutputPath(recursive, hashAlgo, h2, baseName);
     }
         

src/libstore/store-api.hh

@@ -79,9 +79,12 @@ public:
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
        If `fixed' is true, then the output of a fixed-output
-       derivation is pre-loaded into the Nix store. */
+       derivation is pre-loaded into the Nix store.  The function
+       object `filter' can be used to exclude files (see
+       libutil/archive.hh). */
     virtual Path addToStore(const Path & srcPath, bool fixed = false,
-        bool recursive = false, string hashAlgo = "") = 0;
+        bool recursive = false, string hashAlgo = "",
+        PathFilter & filter = defaultPathFilter) = 0;
 
     /* Like addToStore, but the contents written to the output path is
        a regular file containing the given string. */
@@ -195,7 +198,8 @@ Path makeFixedOutputPath(bool recursive,
    Returns the store path and the cryptographic hash of the
    contents of srcPath. */
 std::pair<Path, Hash> computeStorePathForPath(const Path & srcPath,
-    bool fixed = false, bool recursive = false, string hashAlgo = "");
+    bool fixed = false, bool recursive = false, string hashAlgo = "",
+    PathFilter & filter = defaultPathFilter);
 
 /* Preparatory part of addTextToStore().