4 files changed, 50 insertions, 37 deletions

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 5a8f600e8d36..fd16dece7d44 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -4,6 +4,7 @@
 #include "globals.hh"
 #include "store-api.hh"
 #include "util.hh"
+#include "misc.hh"
 
 #include <iostream>
 #include <cctype>
@@ -49,6 +50,34 @@ void printGCWarning()
 }
 
 
+void printMissing(const PathSet & paths)
+{
+    unsigned long long downloadSize;
+    PathSet willBuild, willSubstitute, unknown;
+    queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize);
+
+    if (!willBuild.empty()) {
+        printMsg(lvlInfo, format("the following derivations will be built:"));
+        foreach (PathSet::iterator, i, willBuild)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+
+    if (!willSubstitute.empty()) {
+        printMsg(lvlInfo, format("the following paths will be downloaded/copied (%.2f MiB):") %
+            (downloadSize / (1024.0 * 1024.0)));
+        foreach (PathSet::iterator, i, willSubstitute)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+
+    if (!unknown.empty()) {
+        printMsg(lvlInfo, format("don't know how to build the following paths%1%:")
+            % (readOnlyMode ? " (may be caused by read-only store access)" : ""));
+        foreach (PathSet::iterator, i, unknown)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+}
+
+
 static void setLogType(string lt)
 {
     if (lt == "pretty") logType = ltPretty;
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index 95d80bacdae1..c432dc5f7b56 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -26,6 +26,8 @@ namespace nix {
 Path makeRootName(const Path & gcRoot, int & counter);
 void printGCWarning();
 
+void printMissing(const PathSet & paths);
+
 unsigned long long getIntArg(const string & opt,
     Strings::iterator & i, const Strings::iterator & end);
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index c3fe2d08969b..2f2f263f54a1 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -531,8 +531,8 @@ static void queryInstSources(EvalState & state,
 
 static void printMissing(EvalState & state, const DrvInfos & elems)
 {
-    PathSet targets, willBuild, willSubstitute, unknown;
-    for (DrvInfos::const_iterator i = elems.begin(); i != elems.end(); ++i) {
+    PathSet targets;
+    foreach (DrvInfos::const_iterator, i, elems) {
         Path drvPath = i->queryDrvPath(state);
         if (drvPath != "")
             targets.insert(drvPath);
@@ -540,28 +540,7 @@ static void printMissing(EvalState & state, const DrvInfos & elems)
             targets.insert(i->queryOutPath(state));
     }
 
-    unsigned long long downloadSize;
-    queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize);
-
-    if (!willBuild.empty()) {
-        printMsg(lvlInfo, format("the following derivations will be built:"));
-        foreach (PathSet::iterator, i, willBuild)
-            printMsg(lvlInfo, format("  %1%") % *i);
-    }
-
-    if (!willSubstitute.empty()) {
-        printMsg(lvlInfo, format("the following paths will be downloaded/copied (%.2f MiB):") %
-            (downloadSize / (1024.0 * 1024.0)));
-        foreach (PathSet::iterator, i, willSubstitute)
-            printMsg(lvlInfo, format("  %1%") % *i);
-    }
-
-    if (!unknown.empty()) {
-        printMsg(lvlInfo, format("don't know how to build the following paths%1%:")
-            % (readOnlyMode ? " (may be caused by read-only store access)" : ""));
-        foreach (PathSet::iterator, i, unknown)
-            printMsg(lvlInfo, format("  %1%") % *i);
-    }
+    printMissing(targets);
 }
 
 
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index b59ff27bb30c..0030745b4627 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -77,23 +77,26 @@ static Path realisePath(const Path & path)
 /* Realise the given paths. */
 static void opRealise(Strings opFlags, Strings opArgs)
 {
-    if (!opFlags.empty()) throw UsageError("unknown flag");
+    bool dryRun = false;
+    
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--dry-run") dryRun = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
 
-    for (Strings::iterator i = opArgs.begin();
-         i != opArgs.end(); ++i)
+    foreach (Strings::iterator, i, opArgs)
         *i = followLinksToStorePath(*i);
             
-    if (opArgs.size() > 1) {
-        PathSet drvPaths;
-        for (Strings::iterator i = opArgs.begin();
-             i != opArgs.end(); ++i)
-            if (isDerivation(*i))
-                drvPaths.insert(*i);
-        store->buildDerivations(drvPaths);
-    }
+    printMissing(PathSet(opArgs.begin(), opArgs.end()));
+    
+    if (dryRun) return;
+    
+    /* Build all derivations at the same time to exploit parallelism. */
+    PathSet drvPaths;
+    foreach (Strings::iterator, i, opArgs)
+        if (isDerivation(*i)) drvPaths.insert(*i);
+    store->buildDerivations(drvPaths);
 
-    for (Strings::iterator i = opArgs.begin();
-         i != opArgs.end(); ++i)
+    foreach (Strings::iterator, i,opArgs)
         cout << format("%1%\n") % realisePath(*i);
 }