Add a description in the completion outputs

Make nix output completions in the form `completion\tdescription`.
This can't be used by bash (afaik), but other shells like zsh or fish
can display it along the completion choices

1 files changed, 11 insertions, 1 deletions

diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index f41242e17..26f1bc11b 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -283,7 +283,17 @@ typedef std::vector<std::pair<std::string, std::string>> Table2;
 
 void printTable(std::ostream & out, const Table2 & table);
 
-extern std::shared_ptr<std::set<std::string>> completions;
+struct Completion {
+    std::string completion;
+    std::string description;
+
+    bool operator<(const Completion & other) const;
+};
+class Completions : public std::set<Completion> {
+public:
+    void add(std::string completion, std::string description = "");
+};
+extern std::shared_ptr<Completions> completions;
 extern bool pathCompletions;
 
 std::optional<std::string> needsCompletion(std::string_view s);