From d48c973ece20875391bebde3c167d6e0cc1e666e Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 25 Apr 2017 15:18:05 +0200
Subject: [PATCH] Set default installable

Thus

  $ nix build -f foo.nix

will build foo.nix.

And

  $ nix build

will build default.nix. However, this may not be a good idea because
it's kind of inconsistent, given that "nix build foo" will build the
"foo" attribute from the default installation source (i.e. the
synthesis of $NIX_PATH), rather than ./default.nix. So I may revert
this.
---
 src/nix/installables.cc | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 45517443c..ff345c45d 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -181,6 +181,12 @@ std::vector<std::shared_ptr<Installable>> InstallablesCommand::parseInstallables
 {
     std::vector<std::shared_ptr<Installable>> result;
 
+    if (installables.empty()) {
+        if (file == "")
+            file = ".";
+        installables = Strings{""};
+    }
+
     for (auto & installable : installables) {
 
         if (installable.find("/") != std::string::npos) {
@@ -198,7 +204,7 @@ std::vector<std::shared_ptr<Installable>> InstallablesCommand::parseInstallables
         else if (installable.compare(0, 1, "(") == 0)
             result.push_back(std::make_shared<InstallableExpr>(*this, installable));
 
-        else if (std::regex_match(installable, attrPathRegex))
+        else if (installable == "" || std::regex_match(installable, attrPathRegex))
             result.push_back(std::make_shared<InstallableAttrPath>(*this, installable));
 
         else