* Descriptors now have a "system" field specifying the platform that

the build or run action should be perfomed on.  This ensures that
  descriptors have different hashes on different platforms.

src/Makefile

@@ -1,2 +1,13 @@
+all: nix nix-instantiate
+
+SYSTEM = $(shell ./config.guess)
+
 nix: nix.cc
-	g++ -g -Wall -o nix nix.cc -ldb_cxx-4
+	g++ -g -Wall -o nix nix.cc -ldb_cxx-4 -DSYSTEM=\"$(SYSTEM)\"
+
+nix-instantiate: nix-instantiate.in
+	sed "s/@SYSTEM@/$(SYSTEM)/" < $^ > $@
+	chmod +x $@
+
+clean:
+	rm -f *.o nix nix-instantiate

src/nix-instantiate.in

@@ -4,6 +4,8 @@ use strict;
 use FileHandle;
 use File::Spec;
 
+my $system = "@SYSTEM@";
+
 my $outdir = File::Spec->rel2abs($ARGV[0]);
 my $netdir = File::Spec->rel2abs($ARGV[1]);
 
@@ -49,6 +51,8 @@ sub convert {
     open $IN, "< $descr" or die "cannot open $descr";
     open $OUT, "> $outfile" or die "cannot create $outfile";
 
+    print $OUT "system : $system\n";
+
     while (<$IN>) {
         chomp;
 

src/nix.cc

@@ -34,6 +34,9 @@ static string dbfile = PKGINFO_PATH;
 static string pkgHome = "/pkg";
 
 
+static string thisSystem = SYSTEM;
+
+
 class Error : public exception
 {
     string err;
@@ -177,22 +180,12 @@ string makeRef(string filename)
 }
 
 
-struct Dep
-{
-    string name;
-    string ref;
-    Dep(string _name, string _ref)
-    {
-        name = _name;
-        ref = _ref;
-    }
-};
-
-typedef list<Dep> DepList;
+typedef pair<string, string> Param;
+typedef list<Param> Params;
 
 
 void readPkgDescr(const string & pkgfile,
-    DepList & pkgImports, DepList & fileImports)
+    Params & pkgImports, Params & fileImports, Params & arguments)
 {
     ifstream file;
     file.exceptions(ios::badbit);
@@ -212,12 +205,14 @@ void readPkgDescr(const string & pkgfile,
         string name, op, ref;
         str >> name >> op >> ref;
 
-        checkRef(ref);
-
-        if (op == "<-") 
-            pkgImports.push_back(Dep(name, ref));
-        else if (op == "=")
-            fileImports.push_back(Dep(name, ref));
+        if (op == "<-") {
+            checkRef(ref);
+            pkgImports.push_back(Param(name, ref));
+        } else if (op == "=") {
+            checkRef(ref);
+            fileImports.push_back(Param(name, ref));
+        } else if (op == ":")
+            arguments.push_back(Param(name, ref));
         else throw Error("invalid operator " + op);
     }
 }
@@ -243,37 +238,51 @@ void fetchDeps(string hash, Environment & env)
         throw Error("file " + pkgfile + " is stale");
 
     /* Read the package description file. */
-    DepList pkgImports, fileImports;
-    readPkgDescr(pkgfile, pkgImports, fileImports);
+    Params pkgImports, fileImports, arguments;
+    readPkgDescr(pkgfile, pkgImports, fileImports, arguments);
 
     /* Recursively fetch all the dependencies, filling in the
        environment as we go along. */
-    for (DepList::iterator it = pkgImports.begin();
+    for (Params::iterator it = pkgImports.begin();
          it != pkgImports.end(); it++)
     {
         cerr << "fetching package dependency "
-             << it->name << " <- " << it->ref
+             << it->first << " <- " << it->second
              << endl;
-        env[it->name] = getPkg(it->ref);
+        env[it->first] = getPkg(it->second);
     }
 
-    for (DepList::iterator it = fileImports.begin();
+    for (Params::iterator it = fileImports.begin();
          it != fileImports.end(); it++)
     {
         cerr << "fetching file dependency "
-             << it->name << " = " << it->ref
+             << it->first << " = " << it->second
              << endl;
 
         string file;
 
-        if (!queryDB(dbRefs, it->ref, file))
-            throw Error("unknown file " + it->ref);
+        if (!queryDB(dbRefs, it->second, file))
+            throw Error("unknown file " + it->second);
 
-        if (makeRef(file) != it->ref)
+        if (makeRef(file) != it->second)
             throw Error("file " + file + " is stale");
 
-        env[it->name] = file;
+        env[it->first] = file;
     }
+
+    string buildSystem;
+
+    for (Params::iterator it = arguments.begin();
+         it != arguments.end(); it++)
+    {
+        env[it->first] = it->second;
+        if (it->first == "system")
+            buildSystem = it->second;
+    }
+
+    if (buildSystem != thisSystem)
+        throw Error("descriptor requires a `" + buildSystem +
+            "' but I am a `" + thisSystem + "'");
 }
 
 
@@ -299,7 +308,7 @@ void installPkg(string hash)
     fetchDeps(hash, env);
 
     builder = getFromEnv(env, "build");
-    
+
     /* Construct a path for the installed package. */
     path = pkgHome + "/" + hash;
 

test/tmpl/aterm-2.0.nix

@@ -1,3 +1,5 @@
+id : aterm-2.0
+
 # Original sources.
 src = url(http://www.cwi.nl/projects/MetaEnv/aterm/aterm-2.0.tar.gz)
 

test/tmpl/atk-1.2.0.nix

@@ -1,3 +1,5 @@
+id : atk-1.2.0
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 

test/tmpl/glib-2.2.1.nix

@@ -1,3 +1,5 @@
+id : glib-2.2.1
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 
 src = url(ftp://ftp.gtk.org/pub/gtk/v2.2/glib-2.2.1.tar.bz2)

test/tmpl/gnet-1.1.8.nix

@@ -1,3 +1,5 @@
+id : gnet-1.1.8
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 

test/tmpl/gtk+-2.2.1.nix

@@ -1,3 +1,5 @@
+id : gtk+-2.2.1
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 atk <- ./atk-1.2.0.nix

test/tmpl/gtkspell-2.0.2.nix

@@ -1,3 +1,5 @@
+id : gtkspell-2.0.2
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 atk <- ./atk-1.2.0.nix

test/tmpl/pan-0.13.4.nix

@@ -1,3 +1,5 @@
+id : pan-0.13.4
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 atk <- ./atk-1.2.0.nix

test/tmpl/pan-0.13.91-run.nix

@@ -1,3 +1,5 @@
+id : pan-0.13.91-run
+
 pan <- ./pan-0.13.91.nix
 
 glib <- ./glib-2.2.1.nix

test/tmpl/pan-0.13.91.nix

@@ -1,3 +1,5 @@
+id : pan-0.13.91-run
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 atk <- ./atk-1.2.0.nix

test/tmpl/pango-1.2.1.nix

@@ -1,3 +1,5 @@
+id : pango-1.2.1
+
 pkgconfig <- ./pkgconfig-0.15.0.nix
 glib <- ./glib-2.2.1.nix
 

test/tmpl/pkgconfig-0.15.0.nix

@@ -1,3 +1,5 @@
+id : pkgconfig-0.15.0
+
 src = url(http://www.freedesktop.org/software/pkgconfig/releases/pkgconfig-0.15.0.tar.gz)
 
 build = ../build/pkgconfig-build.sh

test/tmpl/pspell-.12.2.nix

@@ -1,3 +1,5 @@
+id : pspell-.12.2
+
 src = url(http://unc.dl.sourceforge.net/sourceforge/pspell/pspell-.12.2.tar.gz)
 
 build = ../build/pspell-build.sh