* Give unpacked channels more sensible names than 0, 1, ... They now

get the basename of the channel URL (e.g., nixpkgs-unstable).  The
  top-level Nix expression of the channel is now an attribute set, the
  attributes of which are the individual channels (e.g.,
  {nixpkgs_unstable = ...; strategoxt_unstable = ...}).  This makes
  attribute paths ("nix-env -qaA" and "nix-env -iA") more sensible,
  e.g., "nix-env -iA nixpkgs_unstable.subversion".

configure.ac

@@ -139,6 +139,7 @@ fi
 AC_MSG_RESULT(yes)
 
 NEED_PROG(cat, cat)
+NEED_PROG(tr, tr)
 AC_ARG_WITH(coreutils-bin, AC_HELP_STRING([--with-coreutils-bin=PATH],
   [path of cat, mkdir, etc.]),
   coreutils=$withval, coreutils=$(dirname $cat))

corepkgs/channels/unpack.sh.in

@@ -5,18 +5,29 @@
 cd $out/tmp
 
 expr=$out/default.nix
-echo '[' > $expr
+echo '{' > $expr
 
-nr=0
-for i in $inputs; do
-    echo "unpacking $i"
-    @bunzip2@ < $i | @tar@ xf -
-    @coreutils@/mv * ../$nr # !!! hacky
-    echo "(import ./$nr)" >> $expr
-    nr=$(($nr + 1))
+inputs=($inputs)
+for ((n = 0; n < ${#inputs[*]}; n += 2)); do
+    channelName=${inputs[n]}
+    channelTarball=${inputs[n+1]}
+    echo "unpacking channel $channelName"
+    @bunzip2@ < $channelTarball | @tar@ xf -
+
+    nr=1
+    dirName=$channelName
+    while test -e ../$dirName; do
+        nr=$((nr+1))
+        dirName=$channelName-$nr
     done
 
-echo ']' >> $expr
+    @coreutils@/mv * ../$dirName # !!! hacky
+    
+    attrName=$(echo $dirName | @tr@ -- '- ' '__')
+    echo "$attrName = import ./$dirName {};" >> $expr
+done
+
+echo '} // {_combineChannels = true;}' >> $expr
 
 cd ..
 @coreutils@/rmdir tmp

scripts/nix-channel.in

@@ -89,21 +89,22 @@ sub update {
     # Create a Nix expression that fetches and unpacks the channel Nix
     # expressions.
 
-    my $nixExpr = "[";
+    my $inputs = "[";
     foreach my $url (@channels) {
+        $url =~ /\/([^\/]+)\/?$/;
+        my $channelName = $1;
+        $channelName = "unnamed" unless defined $channelName;
+        print "$channelName\n";
+
         my $fullURL = "$url/nixexprs.tar.bz2";
         print "downloading Nix expressions from `$fullURL'...\n";
         $ENV{"PRINT_PATH"} = 1;
         my ($hash, $path) = `@bindir@/nix-prefetch-url '$fullURL' 2> /dev/null`;
         die "cannot fetch `$fullURL'" if $? != 0;
         chomp $path;
-        $nixExpr .= $path . " ";
+        $inputs .= '"' . $channelName . '"' . " " . $path . " ";
     }
-    $nixExpr .= "]";
-
-    $nixExpr =
-        "(import @datadir@/nix/corepkgs/channels/unpack.nix) " .
-        "{inputs = $nixExpr; system = \"@system@\";}";
+    $inputs .= "]";
 
     # Figure out a name for the GC root.
     my $userName = getpwuid($<);
@@ -113,7 +114,7 @@ sub update {
     
     # Instantiate the Nix expression.
     print "unpacking channel Nix expressions...\n";
-    my $storeExpr = `echo '$nixExpr' | @bindir@/nix-instantiate --add-root '$rootFile'.tmp -`
+    my $storeExpr = `@bindir@/nix-instantiate --add-root '$rootFile'.tmp @datadir@/nix/corepkgs/channels/unpack.nix --argstr system @system@ --arg inputs '$inputs'`
         or die "cannot instantiate Nix expression";
     chomp $storeExpr;
 

src/libexpr/get-drvs.cc

@@ -171,11 +171,20 @@ static void getDerivations(EvalState & state, Expr e,
         ATermMap drvMap(ATgetLength(es));
         queryAllAttrs(e, drvMap);
 
+        /* !!! undocumented hackery to support
+           corepkgs/channels/unpack.sh. */
+        Expr e2 = drvMap.get(toATerm("_combineChannels"));
+        bool combineChannels = e2 && evalBool(state, e2);
+        
         for (ATermMap::const_iterator i = drvMap.begin(); i != drvMap.end(); ++i) {
             startNest(nest, lvlDebug,
                 format("evaluating attribute `%1%'") % aterm2String(i->key));
             string pathPrefix2 = addToPath(pathPrefix, aterm2String(i->key));
-            if (getDerivation(state, i->value, pathPrefix2, drvs, doneExprs)) {
+            if (combineChannels) {
+                if (((string) aterm2String(i->key)) != "_combineChannels")
+                    getDerivations(state, i->value, pathPrefix2, autoArgs, drvs, doneExprs);
+            }
+            else if (getDerivation(state, i->value, pathPrefix2, drvs, doneExprs)) {
                 /* If the value of this attribute is itself an
                    attribute set, should we recurse into it?  => Only
                    if it has a `recurseForDerivations = true'
@@ -185,8 +194,8 @@ static void getDerivations(EvalState & state, Expr e,
                 if (matchAttrs(e, es)) {
                     ATermMap attrs(ATgetLength(es));
                     queryAllAttrs(e, attrs, false);
-                    Expr e2 = attrs.get(toATerm("recurseForDerivations"));
-                    if (e2 && evalBool(state, e2))
+                    if (((e2 = attrs.get(toATerm("recurseForDerivations")))
+                            && evalBool(state, e2)))
                         getDerivations(state, e, pathPrefix2, autoArgs, drvs, doneExprs);
                 }
             }

substitute.mk

@@ -17,6 +17,7 @@
 	 -e "s^@perl\@^$(perl)^g" \
 	 -e "s^@coreutils\@^$(coreutils)^g" \
 	 -e "s^@tar\@^$(tar)^g" \
+	 -e "s^@tr\@^$(tr)^g" \
 	 -e "s^@dot\@^$(dot)^g" \
 	 -e "s^@xmllint\@^$(xmllint)^g" \
 	 -e "s^@xmlflags\@^$(xmlflags)^g" \