Pass inputs to release expressions using -I

This means that you can now write (for instance)

  with <nixpkgs> { ... };

in release.nix, rather than

  { nixpkgs } :

  with nixpkgs { ... };

src/c/hydra-eval-jobs.cc

@@ -9,6 +9,7 @@
 #include "util.hh"
 #include "xml-writer.hh"
 #include "get-drvs.hh"
+#include "common-opts.hh"
 
 using namespace nix;
 
@@ -203,6 +204,10 @@ void run(Strings args)
     EvalState state;
     Path releaseExpr;
     AutoArgs autoArgs;
+
+    /* Prevent undeclared dependencies in the evaluation via
+       $HYDRA_PATH. */
+    unsetenv("HYDRA_PATH");
     
     for (Strings::iterator i = args.begin(); i != args.end(); ) {
         string arg = *i++;
@@ -226,6 +231,8 @@ void run(Strings args)
             if (i == args.end()) throw UsageError("missing argument");
             gcRootsDir = *i++;
         }
+        else if (parseSearchPathArg(arg, i, args.end(), state))
+            ;
         else if (arg[0] == '-')
             throw UsageError(format("unknown flag `%1%'") % arg);
         else

src/lib/Hydra/Helper/AddBuilds.pm

@@ -604,6 +604,9 @@ sub inputsToArgs {
     my @res = ();
 
     foreach my $input (keys %{$inputInfo}) {
+        push @res, "-I", "$input=$inputInfo->{$input}->[0]->{storePath}"
+            if scalar @{$inputInfo->{$input}} == 1 
+               && defined $inputInfo->{$input}->[0]->{storePath};
         foreach my $alt (@{$inputInfo->{$input}}) {
             given ($alt->{type}) {
                 when ("string") {

src/script/hydra-evaluator

@@ -115,7 +115,7 @@ sub checkJobset {
     my @args = ($jobset->nixexprinput, $jobset->nixexprpath, inputsToArgs($inputInfo));
     my $argsHash = sha256_hex("@args");
 
-    if ($jobset->jobsetevals->find({hash => $argsHash})) {
+    if (scalar($jobset->jobsetevals->search({hash => $argsHash})) > 0) {
         print "  already evaluated, skipping\n";
         txn_do($db, sub {
             $jobset->update({lastcheckedtime => time});