tweak the parsing of files for flags with disable_flag_override (#800)

* tweak the parsing of files for flags with disable_flag_override, basically allow true as a valid value to be interpreted as the default in that case

* style: pre-commit.ci fixes

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/CLI/impl/App_inl.hpp

@@ -1396,7 +1396,22 @@ CLI11_INLINE bool App::_parse_single_config(const ConfigItem &item, std::size_t
             if(item.inputs.size() <= 1) {
                 // Flag parsing
                 auto res = config_formatter_->to_flag(item);
-                res = op->get_flag_value(item.name, res);
+                bool converted{false};
+                if(op->get_disable_flag_override()) {
+
+                    try {
+                        auto val = detail::to_flag_value(res);
+                        if(val == 1) {
+                            res = op->get_flag_value(item.name, "{}");
+                            converted = true;
+                        }
+                    } catch(...) {
+                    }
+                }
+
+                if(!converted) {
+                    res = op->get_flag_value(item.name, res);
+                }
 
                 op->add_result(res);
                 return true;

tests/ConfigFileTest.cpp

@@ -435,6 +435,8 @@ TEST_CASE("StringBased: file_error", "[config]") {
     CHECK_THROWS_AS(CLI::ConfigINI().from_file("nonexist_file"), CLI::FileError);
 }
 
+static const int fclear1 = fileClear("TestIniTmp.ini");
+
 TEST_CASE_METHOD(TApp, "IniNotRequired", "[config]") {
 
     TempFile tmpini{"TestIniTmp.ini"};
@@ -595,6 +597,8 @@ TEST_CASE_METHOD(TApp, "IniNotRequiredbadConfigurator", "[config]") {
     REQUIRE_NOTHROW(run());
 }
 
+static const int fclear2 = fileClear("TestIniTmp2.ini");
+
 TEST_CASE_METHOD(TApp, "IniNotRequiredNotDefault", "[config]") {
 
     TempFile tmpini{"TestIniTmp.ini"};
@@ -2020,6 +2024,51 @@ TEST_CASE_METHOD(TApp, "IniFalseFlagsDefDisableOverrideSuccess", "[config]") {
     CHECK(val == 15);
 }
 
+static const int fclear3 = fileClear("TestIniTmp3.ini");
+
+TEST_CASE_METHOD(TApp, "IniDisableFlagOverride", "[config]") {
+
+    TempFile tmpini{"TestIniTmp.ini"};
+    TempFile tmpini2{"TestIniTmp2.ini"};
+    TempFile tmpini3{"TestIniTmp3.ini"};
+
+    app.set_config("--config", tmpini);
+
+    {
+        std::ofstream out{tmpini};
+        out << "[default]" << std::endl;
+        out << "two=2" << std::endl;
+    }
+
+    {
+        std::ofstream out{tmpini2};
+        out << "[default]" << std::endl;
+        out << "two=7" << std::endl;
+    }
+
+    {
+        std::ofstream out{tmpini3};
+        out << "[default]" << std::endl;
+        out << "three=true" << std::endl;
+    }
+
+    int val{0};
+    app.add_flag("--one{1},--two{2},--three{3}", val)->disable_flag_override();
+
+    run();
+    CHECK(tmpini.c_str() == app["--config"]->as<std::string>());
+    CHECK(val == 2);
+
+    args = {"--config", tmpini2};
+    CHECK_THROWS_AS(run(), CLI::ArgumentMismatch);
+
+    args = {"--config", tmpini3};
+    run();
+
+    CHECK(val == 3);
+    CHECK(tmpini3.c_str() == app.get_config_ptr()->as<std::string>());
+}
+
 TEST_CASE_METHOD(TApp, "TomlOutputSimple", "[config]") {
 
     int v{0};

tests/app_helper.hpp

@@ -33,6 +33,8 @@ class TApp {
     }
 };
 
+CLI11_INLINE int fileClear(const std::string &name) { return std::remove(name.c_str()); }
+
 class TempFile {
     std::string _name{};