Make the IncorrectConstruction errors on bad subcommand name more comprehensible.

Author: phlptp

include/CLI/App.hpp

@@ -368,7 +368,20 @@ class App {
     /// Set an alias for the app
     App *alias(std::string app_name) {
         if(!detail::valid_name_string(app_name)) {
-            throw(IncorrectConstruction("alias is not a valid name string"));
+            if(app_name.empty()) {
+                throw IncorrectConstruction("Empty aliases are not allowed");
+            }
+            if(!detail::valid_first_char(app_name[0])) {
+                throw IncorrectConstruction(
+                    "Alias starts with invalid character, allowed characters are [a-zA-z0-9]+'_','?','@' ");
+            }
+            for(auto c : app_name) {
+                if(!detail::valid_later_char(c)) {
+                    throw IncorrectConstruction(std::string("Alias contains invalid character ('") + c +
+                                                "'), allowed characters are "
+                                                "[a-zA-z0-9]+'_','?','@','.','-' ");
+                }
+            }
         }
 
         if(parent_ != nullptr) {
@@ -1013,7 +1026,17 @@ class App {
     /// Add a subcommand. Inherits INHERITABLE and OptionDefaults, and help flag
     App *add_subcommand(std::string subcommand_name = "", std::string subcommand_description = "") {
         if(!subcommand_name.empty() && !detail::valid_name_string(subcommand_name)) {
-            throw IncorrectConstruction("subcommand name is not valid");
+            if(!detail::valid_first_char(subcommand_name[0])) {
+                throw IncorrectConstruction(
+                    "Subcommand name starts with invalid character, allowed characters are [a-zA-z0-9]+'_','?','@' ");
+            }
+            for(auto c : subcommand_name) {
+                if(!detail::valid_later_char(c)) {
+                    throw IncorrectConstruction(std::string("Subcommand name contains invalid character ('") + c +
+                                                "'), allowed characters are "
+                                                "[a-zA-z0-9]+'_','?','@','.','-' ");
+                }
+            }
         }
         CLI::App_p subcom = std::shared_ptr<App>(new App(std::move(subcommand_description), subcommand_name, this));
         return add_subcommand(std::move(subcom));
@@ -3158,25 +3181,25 @@ struct AppFriend {
 #ifdef CLI11_CPP14
 
     /// Wrap _parse_short, perfectly forward arguments and return
-    template <typename... Args> static decltype(auto) parse_arg(App *app, Args &&... args) {
+    template <typename... Args> static decltype(auto) parse_arg(App *app, Args &&...args) {
         return app->_parse_arg(std::forward<Args>(args)...);
     }
 
     /// Wrap _parse_subcommand, perfectly forward arguments and return
-    template <typename... Args> static decltype(auto) parse_subcommand(App *app, Args &&... args) {
+    template <typename... Args> static decltype(auto) parse_subcommand(App *app, Args &&...args) {
         return app->_parse_subcommand(std::forward<Args>(args)...);
     }
 #else
     /// Wrap _parse_short, perfectly forward arguments and return
     template <typename... Args>
-    static auto parse_arg(App *app, Args &&... args) ->
+    static auto parse_arg(App *app, Args &&...args) ->
         typename std::result_of<decltype (&App::_parse_arg)(App, Args...)>::type {
         return app->_parse_arg(std::forward<Args>(args)...);
     }
 
     /// Wrap _parse_subcommand, perfectly forward arguments and return
     template <typename... Args>
-    static auto parse_subcommand(App *app, Args &&... args) ->
+    static auto parse_subcommand(App *app, Args &&...args) ->
         typename std::result_of<decltype (&App::_parse_subcommand)(App, Args...)>::type {
         return app->_parse_subcommand(std::forward<Args>(args)...);
     }

tests/SubcommandTest.cpp

@@ -811,6 +811,18 @@ TEST_CASE_METHOD(TApp, "RequiredPosInSubcommand", "[subcom]") {
     CHECK_THROWS_AS(run(), CLI::RequiredError);
 }
 
+TEST_CASE_METHOD(TApp, "invalidSubcommandName", "[subcom]") {
+
+    bool gotError{false};
+    try {
+        app.add_subcommand("foo/foo", "Foo a bar");
+    } catch(const CLI::IncorrectConstruction &e) {
+        gotError = true;
+        CHECK_THAT(e.what(), Contains("/"));
+    }
+    CHECK(gotError);
+}
+
 struct SubcommandProgram : public TApp {
 
     CLI::App *start{nullptr};