Fix usage of structured attrs for nix develop

src/nix/develop.cc

@@ -256,6 +256,11 @@ struct Common : InstallableCommand, MixProfile
         // FIXME: properly unquote 'outputs'.
         StringMap rewrites;
         for (auto & outputName : tokenizeString<std::vector<std::string>>(replaceStrings(outputs->second.quoted, "'", ""))) {
+            std::regex ptrn(R"re(\[([A-z0-9]+)\]=.*)re");
+            std::smatch match;
+            if (std::regex_match(outputName, match, ptrn)) {
+                outputName = match[1];
+            }
             auto from = buildEnvironment.env.find(outputName);
             assert(from != buildEnvironment.env.end());
             // FIXME: unquote

src/nix/get-env.sh

@@ -8,7 +8,13 @@ if [[ -n $stdenv ]]; then
     source $stdenv/setup
 fi
 
-for __output in $outputs; do
+if [ -e .attrs.sh ]; then
+    __olist="${!outputs[@]}"
+else
+    __olist=$outputs
+fi
+
+for __output in $__olist; do
     if [[ -z $__done ]]; then
         export > ${!__output}
         set >> ${!__output}