From d3e1aad421a88a7a075cac25142c49224b3ecca2 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Fri, 24 Feb 2017 17:25:00 +0100
Subject: [PATCH] nix-shell: Better error message when the shell can't be
 started

---
 src/nix-build/nix-build.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index f4484ba57..b81c98868 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -448,15 +448,17 @@ int main(int argc, char ** argv)
 
                 auto envPtrs = stringsToCharPtrs(envStrs);
 
+                auto shell = getEnv("NIX_BUILD_SHELL", "bash");
+
                 environ = envPtrs.data();
 
                 auto argPtrs = stringsToCharPtrs(args);
 
                 restoreSignals();
 
-                execvp(getEnv("NIX_BUILD_SHELL", "bash").c_str(), argPtrs.data());
+                execvp(shell.c_str(), argPtrs.data());
 
-                throw SysError("executing shell");
+                throw SysError("executing shell ‘%s’", shell);
             }
 
             // Ugly hackery to make "nix-build -A foo.all" produce symlinks