* nix-env: allow ~/.nix-defexpr to be a directory. If it is, then the

Nix expressions in that directory are combined into an attribute set
  {file1 = import file1; file2 = import file2; ...}, i.e. each Nix
  expression is an attribute with the file name as the attribute
  name.  Also recurses into directories.

* nix-env: removed the "--import" (-I) option which set the
  ~/.nix-defexpr symlink.

* nix-channel: don't use "nix-env --import", instead symlink
  ~/.nix-defexpr/channels.  So finally nix-channel --update doesn't
  override any default Nix expressions but combines with them.

  This means that you can have (say) a local Nixpkgs SVN tree and use
  it as a default for nix-env:

  $ ln -s .../path-to-nixpkgs-tree ~/.nix-defexpr/nixpkgs_svn

  and be subscribed to channels (including Nixpkgs) at the same time.
  (If there is any ambiguity, the -A flag can be used to
  disambiguate, e.g. "nix-env -i -A nixpkgs_svn.pan".)

corepkgs/channels/unpack.sh.in

@@ -4,9 +4,6 @@
 @coreutils@/mkdir $out/tmp
 cd $out/tmp
 
-expr=$out/default.nix
-echo '{' > $expr
-
 inputs=($inputs)
 for ((n = 0; n < ${#inputs[*]}; n += 2)); do
     channelName=${inputs[n]}
@@ -15,19 +12,15 @@ for ((n = 0; n < ${#inputs[*]}; n += 2)); do
     @bunzip2@ < $channelTarball | @tar@ xf -
 
     nr=1
-    dirName=$channelName
+    attrName=$(echo $channelName | @tr@ -- '- ' '__')
+    dirName=$attrName
     while test -e ../$dirName; do
         nr=$((nr+1))
-        dirName=$channelName-$nr
+        dirName=$attrName-$nr
     done
 
     @coreutils@/mv * ../$dirName # !!! hacky
-    
-    attrName=$(echo $dirName | @tr@ -- '- ' '__')
-    echo "$attrName = let e = import ./$dirName; in if builtins.isFunction e then e {} else e;" >> $expr
 done
 
-echo '} // {_combineChannels = true;}' >> $expr
-
 cd ..
 @coreutils@/rmdir tmp

doc/manual/nix-env.xml

@@ -142,14 +142,14 @@ linkend="sec-common-options" />.</para>
 <variablelist>
 
   <varlistentry><term><filename>~/.nix-defexpr</filename></term>
+
+  <!-- !!! .nix-defexpr can be a directory now -->
   
     <listitem><para>The default Nix expression used by the
     <option>--install</option>, <option>--upgrade</option>, and
     <option>--query --available</option> operations to obtain
-    derivations.  It is generally a symbolic link to some other
-    location set using the <option>--import</option> operation.  The
-    <option>--file</option> option may be used to override this
-    default.</para></listitem>
+    derivations.  The <option>--file</option> option may be used to
+    override this default.</para></listitem>
     
   </varlistentry>
 
@@ -1061,43 +1061,4 @@ error: no generation older than the current (91) exists</screen>
 
 
   
-<!--######################################################################-->
-
-<refsection><title>Operation <option>--import</option></title>
-
-<refsection><title>Synopsis</title>
-
-<cmdsynopsis>
-  <command>nix-env</command>
-  <group choice='req'>
-    <arg choice='plain'><option>--import</option></arg>
-    <arg choice='plain'><option>-I</option></arg>
-  </group>
-  <arg choice='req'><replaceable>path</replaceable></arg>
-</cmdsynopsis>
-
-</refsection>
-
-
-<refsection><title>Description</title>
-            
-<para>This operation makes <replaceable>path</replaceable> the default
-active Nix expression for the user.  That is, the symlink
-<filename>~/.nix-userenv</filename> is made to point to
-<replaceable>path</replaceable>.</para>
-
-</refsection>
-
-
-<refsection><title>Examples</title>
-
-<screen>
-$ nix-env -I ~/nixpkgs-0.5/</screen>
-
-</refsection>
-    
-</refsection>
-
-
-  
 </refentry>

scripts/nix-channel.in

@@ -18,6 +18,8 @@ $ENV{'NIX_DOWNLOAD_CACHE'} = $channelCache if -W $channelCache;
 my $home = $ENV{"HOME"};
 die '$HOME not set' unless defined $home;
 my $channelsList = "$home/.nix-channels";
+
+my $nixDefExpr = "$home/.nix-defexpr";
     
 
 my @channels;
@@ -136,9 +138,12 @@ sub update {
 
     unlink "$rootFile.tmp";
 
-    # Make it the default Nix expression for `nix-env'.
-    system("@bindir@/nix-env", "--import", "$outPath") == 0
-         or die "cannot pull set default Nix expression to `$outPath'";
+    # Make the channels appear in nix-env.
+    unlink $nixDefExpr if -l $nixDefExpr; # old-skool ~/.nix-defexpr
+    mkdir $nixDefExpr or die "cannot create directory `$nixDefExpr'" if !-e $nixDefExpr;
+    my $channelLink = "$nixDefExpr/channels";
+    unlink $channelLink; # !!! not atomic
+    symlink($outPath, $channelLink) or die "cannot symlink `$channelLink' to `$outPath'";
 }
 
 

src/libexpr/get-drvs.cc

@@ -171,8 +171,8 @@ static void getDerivations(EvalState & state, Expr e,
         ATermMap drvMap(ATgetLength(es));
         queryAllAttrs(e, drvMap);
 
-        /* !!! undocumented hackery to support
-           corepkgs/channels/unpack.sh. */
+        /* !!! undocumented hackery to support combining channels in
+           nix-env.cc. */
         Expr e2 = drvMap.get(toATerm("_combineChannels"));
         bool combineChannels = e2 && evalBool(state, e2);
         

src/libutil/util.cc

@@ -154,6 +154,7 @@ bool pathExists(const Path & path)
 
 Path readLink(const Path & path)
 {
+    checkInterrupt();
     struct stat st;
     if (lstat(path.c_str(), &st))
         throw SysError(format("getting status of `%1%'") % path);

src/nix-env/nix-env.cc

@@ -22,6 +22,8 @@
 #include <iostream>
 #include <sstream>
 
+#include <sys/types.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 
@@ -72,11 +74,53 @@ void printHelp()
 }
 
 
+static bool isNixExpr(const Path & path)
+{
+    struct stat st;
+    if (stat(path.c_str(), &st) == -1)
+        throw SysError(format("getting information about `%1%'") % path);
+
+    return !S_ISDIR(st.st_mode) || pathExists(path + "/default.nix");
+}
+
+
+static void getAllExprs(EvalState & state,
+    const Path & path, ATermMap & attrs)
+{
+    Strings names = readDirectory(path);
+
+    for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
+        Path path2 = path + "/" + *i;
+        if (isNixExpr(path2))
+            attrs.set(toATerm(*i), makeAttrRHS(
+                    parseExprFromFile(state, absPath(path2)), makeNoPos()));
+        else
+            getAllExprs(state, path2, attrs);
+    }
+}
+
+
+static Expr loadSourceExpr(EvalState & state, const Path & path)
+{
+    if (isNixExpr(path)) return parseExprFromFile(state, absPath(path));
+
+    /* The path is a directory.  Put the Nix expressions in the
+       directory in an attribute set, with the file name of each
+       expression as the attribute name.  Recurse into subdirectories
+       (but keep the attribute set flat, not nested, to make it easier
+       for a user to have a ~/.nix-defexpr directory that includes
+       some system-wide directory). */
+    ATermMap attrs;
+    attrs.set(toATerm("_combineChannels"), makeAttrRHS(eTrue, makeNoPos()));
+    getAllExprs(state, path, attrs);
+    return makeAttrs(attrs);
+}
+
+
 static void loadDerivations(EvalState & state, Path nixExprPath,
     string systemFilter, const ATermMap & autoArgs, DrvInfos & elems)
 {
-    getDerivations(state,
-        parseExprFromFile(state, absPath(nixExprPath)), "", autoArgs, elems);
+    getDerivations(state, loadSourceExpr(state, nixExprPath), "", autoArgs, elems);
 
     /* Filter out all derivations not applicable to the current
        system. */
@@ -365,9 +409,7 @@ static void queryInstSources(EvalState & state,
            (import ./foo.nix)' = `(import ./foo.nix).bar'. */
         case srcNixExprs: {
                 
-
-            Expr e1 = parseExprFromFile(state,
-                absPath(instSource.nixExprPath));
+            Expr e1 = loadSourceExpr(state, instSource.nixExprPath);
 
             for (Strings::const_iterator i = args.begin();
                  i != args.end(); ++i)
@@ -429,7 +471,7 @@ static void queryInstSources(EvalState & state,
                  i != args.end(); ++i)
                 getDerivations(state,
                     findAlongAttrPath(state, *i, instSource.autoArgs,
-                        parseExprFromFile(state, instSource.nixExprPath)),
+                        loadSourceExpr(state, instSource.nixExprPath)),
                     "", instSource.autoArgs, elems);
             break;
         }
@@ -1218,18 +1260,6 @@ static void opDeleteGenerations(Globals & globals,
 }
 
 
-static void opDefaultExpr(Globals & globals,
-    Strings opFlags, Strings opArgs)
-{
-    if (opFlags.size() > 0)
-        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
-    if (opArgs.size() != 1)
-        throw UsageError(format("exactly one argument expected"));
-
-    switchLink(getDefNixExprPath(), absPath(opArgs.front()));
-}
-
-
 static string needArg(Strings::iterator & i,
     Strings & args, const string & arg)
 {
@@ -1286,8 +1316,6 @@ void run(Strings args)
             op = opSet;
         else if (arg == "--query" || arg == "-q")
             op = opQuery;
-        else if (arg == "--import" || arg == "-I") /* !!! bad name */
-            op = opDefaultExpr;
         else if (arg == "--profile" || arg == "-p")
             globals.profile = absPath(needArg(i, args, arg));
         else if (arg == "--file" || arg == "-f")