Implement a suggestions mechanism

Each `Error` class now includes a set of suggestions, and these are printed by
the top-level handler.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index f970c0e9e..69aa0d094 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -328,8 +328,13 @@ MultiCommand::MultiCommand(const Commands & commands_)
                         completions->add(name);
             }
             auto i = commands.find(s);
-            if (i == commands.end())
-                throw UsageError("'%s' is not a recognised command", s);
+            if (i == commands.end()) {
+                std::set<std::string> commandNames;
+                for (auto & [name, _] : commands)
+                    commandNames.insert(name);
+                auto suggestions = Suggestions::bestMatches(commandNames, s);
+                throw UsageError(suggestions, "'%s' is not a recognised command", s);
+            }
             command = {s, i->second()};
             command->second->parent = this;
         }}