getDerivations(): Filter out packages with bad derivation names

In particular, this disallows attribute names containing dots or
starting with dots. Hydra already disallowed these. This affects the
following packages in Nixpkgs master:

  2048-in-terminal
  2bwm
  389-ds-base
  90secondportraits
  lispPackages.3bmd
  lispPackages.hu.dwim.asdf
  lispPackages.hu.dwim.def

Closes #1342.

src/libexpr/get-drvs.cc

@@ -3,6 +3,7 @@
 #include "eval-inline.hh"
 
 #include <cstring>
+#include <regex>
 
 
 namespace nix {
@@ -262,6 +263,9 @@ static string addToPath(const string & s1, const string & s2)
 }
 
 
+static std::regex attrRegex("[A-Za-z_][A-Za-z0-9-_+]*");
+
+
 static void getDerivations(EvalState & state, Value & vIn,
     const string & pathPrefix, Bindings & autoArgs,
     DrvInfos & drvs, Done & done,
@@ -286,6 +290,8 @@ static void getDerivations(EvalState & state, Value & vIn,
            precedence). */
         for (auto & i : v.attrs->lexicographicOrder()) {
             Activity act(*logger, lvlDebug, format("evaluating attribute ‘%1%’") % i->name);
+            if (!std::regex_match(std::string(i->name), attrRegex))
+                continue;
             string pathPrefix2 = addToPath(pathPrefix, i->name);
             if (combineChannels)
                 getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);