Add a ! operator to Validators for checking a false condition

include/CLI/App.hpp

@@ -291,7 +291,7 @@ class App {
         return this;
     }
 
-    /// specify that the positional arguments are only at the end of the sequence
+    /// Specify that the positional arguments are only at the end of the sequence
     App *positionals_at_end(bool value = true) {
         positionals_at_end_ = value;
         return this;

include/CLI/Validators.hpp

@@ -96,6 +96,29 @@ class Validator {
         };
         return newval;
     }
+
+    /// Create a validator that fails when a given validator succeeds
+    Validator operator!() const {
+        Validator newval;
+        std::string typestring = tname;
+        if(tname.empty()) {
+            typestring = tname_function();
+        }
+        newval.tname = "NOT " + typestring;
+
+        std::string failString = "check " + typestring + " succeeded improperly";
+        // Give references (will make a copy in lambda function)
+        const std::function<std::string(std::string & res)> &f1 = func;
+
+        newval.func = [f1, failString](std::string &test) -> std::string {
+            std::string s1 = f1(test);
+            if(s1.empty())
+                return failString;
+            else
+                return std::string();
+        };
+        return newval;
+    }
 };
 
 // The implementation of the built in validators is using the Validator class;

tests/AppTest.cpp

@@ -1317,6 +1317,24 @@ TEST_F(TApp, FileExists) {
     EXPECT_FALSE(CLI::ExistingFile(myfile).empty());
 }
 
+TEST_F(TApp, NotFileExists) {
+    std::string myfile{"TestNonFileNotUsed.txt"};
+    EXPECT_FALSE(CLI::ExistingFile(myfile).empty());
+
+    std::string filename = "Failed";
+    app.add_option("--file", filename)->check(!CLI::ExistingFile);
+    args = {"--file", myfile};
+
+    EXPECT_NO_THROW(run());
+
+    bool ok = static_cast<bool>(std::ofstream(myfile.c_str()).put('a')); // create file
+    EXPECT_TRUE(ok);
+    EXPECT_THROW(run(), CLI::ValidationError);
+
+    std::remove(myfile.c_str());
+    EXPECT_FALSE(CLI::ExistingFile(myfile).empty());
+}
+
 TEST_F(TApp, VectorFixedString) {
     std::vector<std::string> strvec;
     std::vector<std::string> answer{"mystring", "mystring2", "mystring3"};

tests/SetTest.cpp

@@ -337,6 +337,20 @@ TEST_F(TApp, InSetIgnoreCasePointer) {
     EXPECT_THROW(run(), CLI::ArgumentMismatch);
 }
 
+TEST_F(TApp, NotInSetIgnoreCasePointer) {
+
+    std::set<std::string> *options = new std::set<std::string>{"one", "Two", "THREE"};
+    std::string choice;
+    app.add_option("-q,--quick", choice)->check(!CLI::IsMember(*options, CLI::ignore_case));
+
+    args = {"--quick", "One"};
+    EXPECT_THROW(run(), CLI::ValidationError);
+
+    args = {"--quick", "four"};
+    run();
+    EXPECT_EQ(choice, "four");
+}
+
 TEST_F(TApp, InSetIgnoreUnderscore) {
 
     std::string choice;