feat(cli): add shell completion command (bash)

- introduce 'vix completion' command
- generate bash completion script from dispatcher entries
- remove dependency on bash-completion (_init_completion)
- enable tab completion for commands and 'vix help <cmd>'
- integrate completion into CLI help output

Usage:
  source <(vix completion bash)

Author: GaspardKirira

include/vix/cli/commands/CompletionCommand.hpp

@@ -0,0 +1,29 @@
+/**
+ *
+ *  @file CompletionCommand.hpp
+ *  @author Gaspard Kirira
+ *
+ *  Copyright 2025, Gaspard Kirira.  All rights reserved.
+ *  https://github.com/vixcpp/vix
+ *  Use of this source code is governed by a MIT license
+ *  that can be found in the License file.
+ *
+ *  Vix.cpp
+ *
+ */
+#ifndef VIX_COMPLETION_COMMAND_HPP
+#define VIX_COMPLETION_COMMAND_HPP
+
+#include <vector>
+#include <string>
+
+namespace vix::commands
+{
+  struct CompletionCommand
+  {
+    static int run(const std::vector<std::string> &args);
+    static int help();
+  };
+}
+
+#endif

src/CLI.cpp

@@ -42,6 +42,7 @@
 #include <vix/cli/commands/UpdateCommand.hpp>
 #include <vix/cli/commands/OutdatedCommand.hpp>
 #include <vix/cli/commands/MakeCommand.hpp>
+#include <vix/cli/commands/CompletionCommand.hpp>
 #include <vix/utils/Env.hpp>
 #include <vix/cli/Style.hpp>
 #include <vix/utils/Logger.hpp>
@@ -345,14 +346,17 @@ namespace vix
     {
       if (!dispatcher.has(cmd))
       {
-        std::cerr << "error: unrecognized subcommand\n\n";
+        vix::cli::util::err_line(
+            std::cerr,
+            "unrecognized subcommand " + vix::cli::util::quote(cmd));
 
         auto suggestion = find_closest_command(cmd, dispatcher.entries());
 
         if (suggestion.has_value())
         {
-          std::cerr << "  tip: a similar command exists: '"
-                    << suggestion.value() << "'\n";
+          vix::cli::util::tip_line(
+              std::cerr,
+              "A similar command exists: " + vix::cli::util::quote(suggestion.value()));
         }
 
         return 1;
@@ -371,14 +375,17 @@ namespace vix
 
     if (!dispatcher.has(cmd))
     {
-      std::cerr << "error: unrecognized subcommand\n\n";
+      vix::cli::util::err_line(
+          std::cerr,
+          "unrecognized subcommand " + vix::cli::util::quote(cmd));
 
       auto suggestion = find_closest_command(cmd, dispatcher.entries());
 
       if (suggestion.has_value())
       {
-        std::cerr << "  tip: a similar command exists: '"
-                  << suggestion.value() << "'\n";
+        vix::cli::util::tip_line(
+            std::cerr,
+            "A similar command exists: " + vix::cli::util::quote(suggestion.value()));
       }
 
       return 1;
@@ -444,6 +451,8 @@ namespace vix
         return commands::StoreCommand::help();
       if (cmd == "publish")
         return commands::PublishCommand::help();
+      if (cmd == "completion")
+        return commands::CompletionCommand::help();
       if (cmd == "deps")
       {
         vix::cli::util::warn_line(std::cout, "'vix deps' is deprecated, use 'vix install'");
@@ -552,6 +561,7 @@ namespace vix
     // Help
     out << indent(2) << "Help:\n";
     out << indent(3) << "help [command]    Show command help\n";
+    out << indent(3) << "completion        Generate shell completion script\n";
     out << indent(3) << "version           Show version\n\n";
 
     out << indent(1) << "Global options:\n";

src/commands/CompletionCommand.cpp

@@ -0,0 +1,104 @@
+/**
+ *
+ *  @file CompletionCommand.hpp
+ *  @author Gaspard Kirira
+ *
+ *  Copyright 2025, Gaspard Kirira.  All rights reserved.
+ *  https://github.com/vixcpp/vix
+ *  Use of this source code is governed by a MIT license
+ *  that can be found in the License file.
+ *
+ *  Vix.cpp
+ *
+ */
+#include <vix/cli/commands/CompletionCommand.hpp>
+#include <vix/cli/commands/Dispatch.hpp>
+
+#include <iostream>
+#include <vector>
+#include <string>
+#include <algorithm>
+
+namespace vix::commands
+{
+  namespace
+  {
+    std::vector<std::string> collect_commands()
+    {
+      std::vector<std::string> names;
+
+      const auto &entries = vix::cli::dispatch::global().entries();
+      names.reserve(entries.size());
+
+      for (const auto &[name, _] : entries)
+      {
+        names.push_back(name);
+      }
+
+      std::sort(names.begin(), names.end());
+      return names;
+    }
+
+    int print_bash()
+    {
+      const auto commands = collect_commands();
+
+      std::cout << "_vix_completions()\n";
+      std::cout << "{\n";
+      std::cout << "  local cur prev\n";
+      std::cout << "  cur=\"${COMP_WORDS[COMP_CWORD]}\"\n";
+      std::cout << "  prev=\"${COMP_WORDS[COMP_CWORD-1]}\"\n\n";
+
+      std::cout << "  local commands=\"";
+      for (size_t i = 0; i < commands.size(); ++i)
+      {
+        if (i != 0)
+          std::cout << " ";
+        std::cout << commands[i];
+      }
+      std::cout << "\"\n\n";
+
+      std::cout << "  if [[ ${COMP_CWORD} -eq 1 ]]; then\n";
+      std::cout << "    COMPREPLY=( $(compgen -W \"$commands\" -- \"$cur\") )\n";
+      std::cout << "    return 0\n";
+      std::cout << "  fi\n\n";
+
+      std::cout << "  case \"${COMP_WORDS[1]}\" in\n";
+      std::cout << "    help)\n";
+      std::cout << "      COMPREPLY=( $(compgen -W \"$commands\" -- \"$cur\") )\n";
+      std::cout << "      return 0\n";
+      std::cout << "      ;;\n";
+      std::cout << "  esac\n\n";
+
+      std::cout << "  COMPREPLY=()\n";
+      std::cout << "}\n\n";
+
+      std::cout << "complete -o default -F _vix_completions vix\n";
+      return 0;
+    }
+  }
+
+  int CompletionCommand::run(const std::vector<std::string> &args)
+  {
+    if (args.empty() || args[0] == "bash")
+      return print_bash();
+
+    if (args[0] == "--help" || args[0] == "-h")
+      return help();
+
+    std::cerr << "vix completion: unsupported shell '" << args[0] << "'\n";
+    std::cerr << "Supported: bash\n";
+    return 1;
+  }
+
+  int CompletionCommand::help()
+  {
+    std::cout
+        << "vix completion [bash]\n\n"
+        << "Generate shell completion script.\n\n"
+        << "Examples:\n"
+        << "  vix completion bash > ~/.vix-completion.bash\n"
+        << "  source ~/.vix-completion.bash\n";
+    return 0;
+  }
+}

src/commands/Dispatch.cpp

@@ -41,6 +41,7 @@
 #include <vix/cli/commands/OutdatedCommand.hpp>
 #include <vix/cli/commands/MakeCommand.hpp>
 #include <vix/cli/util/Ui.hpp>
+#include <vix/cli/commands/CompletionCommand.hpp>
 
 #include <stdexcept>
 
@@ -62,6 +63,14 @@ namespace vix::cli::dispatch
          []()
          { return vix::commands::NewCommand::help(); }});
 
+    add({"completion",
+         "Info",
+         "Generate shell completion script",
+         [](const Args &a)
+         { return vix::commands::CompletionCommand::run(a); },
+         []()
+         { return vix::commands::CompletionCommand::help(); }});
+
     add({"build",
          "Project",
          "Configure + build project",