Regenerate shell-candidates for each completion sessions

That should allow fixing the #665 issue while still avoiding to
run a potentially long shell command on each keystroke.

src/command_manager.cc

@@ -609,6 +609,11 @@ Completions CommandManager::complete(const Context& context,
             return Completions{};
 
         const String& command_name = tokens[cmd_idx].content();
+        if (command_name != m_last_complete_command)
+        {
+            m_last_complete_command = command_name;
+            flags |= CompletionFlags::Start;
+        }
 
         auto command_it = find_command(context, command_name);
         if (command_it == m_commands.end() or
@@ -652,6 +657,11 @@ Completions CommandManager::complete(const Context& context,
     else
     {
         const String& command_name = params[0];
+        if (command_name != m_last_complete_command)
+        {
+            m_last_complete_command = command_name;
+            flags |= CompletionFlags::Start;
+        }
 
         auto command_it = find_command(context, command_name);
         if (command_it != m_commands.end() and command_it->second.completer)

src/command_manager.hh

@@ -126,6 +126,8 @@ public:
 
     Completions complete_command_name(const Context& context, StringView query, bool with_aliases) const;
 
+    void clear_last_complete_command() { m_last_complete_command = String{}; }
+
 private:
     void execute_single_command(CommandParameters params,
                                 Context& context,
@@ -143,6 +145,7 @@ private:
     };
     using CommandMap = UnorderedMap<String, CommandDescriptor, MemoryDomain::Commands>;
     CommandMap m_commands;
+    String m_last_complete_command;
 
     CommandMap::const_iterator find_command(const Context& context,
                                             const String& name) const;

src/commands.cc

@@ -843,7 +843,7 @@ void define_command(const ParametersParser& parser, Context& context, const Shel
                         CommandParameters params,
                         size_t token_to_complete, ByteCount pos_in_token)
         {
-            if (flags == CompletionFlags::Fast) // no shell on fast completion
+            if (flags & CompletionFlags::Fast) // no shell on fast completion
                 return Completions{};
 
             ShellContext shell_context{
@@ -866,9 +866,12 @@ void define_command(const ParametersParser& parser, Context& context, const Shel
             const Context& context, CompletionFlags flags, CommandParameters params,
             size_t token_to_complete, ByteCount pos_in_token) mutable
         {
+            if (flags & CompletionFlags::Start)
+                token = -1;
+
             if (token != token_to_complete)
             {
-                if (flags == CompletionFlags::Fast) // no shell on fast completion
+                if (flags & CompletionFlags::Fast) // no shell on fast completion
                     return Completions{};
 
                 ShellContext shell_context{
@@ -884,9 +887,6 @@ void define_command(const ParametersParser& parser, Context& context, const Shel
                 token = token_to_complete;
             }
 
-            if (token != token_to_complete)
-                return Completions{};
-
             StringView query = params[token_to_complete].substr(0, pos_in_token);
             UsedLetters query_letters = used_letters(query);
             Vector<RankedMatch> matches;

src/completion.hh

@@ -4,6 +4,7 @@
 #include <functional>
 #include <algorithm>
 
+#include "flags.hh"
 #include "units.hh"
 #include "string.hh"
 #include "vector.hh"
@@ -34,9 +35,13 @@ struct Completions
 
 enum class CompletionFlags
 {
-    None,
+    None = 0,
-    Fast
+    Fast = 1 << 0,
+    Start = 1 << 2,
 };
+
+template<> struct WithBitOps<CompletionFlags> : std::true_type {};
+
 using Completer = std::function<Completions (const Context&, CompletionFlags,
                                              StringView, ByteCount)>;
 

src/normal.cc

@@ -335,6 +335,8 @@ void command(Context& context, NormalParams params)
     if (not CommandManager::has_instance())
         return;
 
+    CommandManager::instance().clear_last_complete_command();
+
     context.input_handler().prompt(
         ":", "", get_face("Prompt"), false,
         [](const Context& context, CompletionFlags flags,