fix!: Limit Setting FromStrs to YAML

These exist pretty much just for YAML (#3087).  If anyone else is
building on these, it has a limited shelf-life anyways because of #2717.

BREAKING CHANGE: `FromStr` for settings requires the `yaml` feature.

src/build/app/settings.rs

@@ -1,5 +1,7 @@
 // Std
-use std::{ops::BitOr, str::FromStr};
+use std::ops::BitOr;
+#[cfg(feature = "yaml")]
+use std::str::FromStr;
 
 // Third party
 use bitflags::bitflags;
@@ -1158,11 +1160,12 @@ impl_settings! { AppSettings, AppFlags,
 
 #[cfg(test)]
 mod test {
-    use super::AppSettings;
-
     #[allow(clippy::cognitive_complexity)]
     #[test]
+    #[cfg(feature = "yaml")]
     fn app_settings_fromstr() {
+        use super::AppSettings;
+
         assert_eq!(
             "disablehelpflag".parse::<AppSettings>().unwrap(),
             AppSettings::DisableHelpFlag

src/build/arg/settings.rs

@@ -1,5 +1,7 @@
 // Std
-use std::{ops::BitOr, str::FromStr};
+use std::ops::BitOr;
+#[cfg(feature = "yaml")]
+use std::str::FromStr;
 
 // Third party
 use bitflags::bitflags;
@@ -157,10 +159,11 @@ impl_settings! { ArgSettings, ArgFlags,
 
 #[cfg(test)]
 mod test {
-    use super::ArgSettings;
-
     #[test]
+    #[cfg(feature = "yaml")]
     fn arg_settings_fromstr() {
+        use super::ArgSettings;
+
         assert_eq!(
             "allowhyphenvalues".parse::<ArgSettings>().unwrap(),
             ArgSettings::AllowHyphenValues

src/macros.rs

@@ -879,6 +879,8 @@ macro_rules! impl_settings {
             }
         }
 
+        /// Deprecated in [Issue #3087](https://github.com/clap-rs/clap/issues/3087), maybe [`clap::Parser`][crate::Parser] would fit your use case?
+        #[cfg(feature = "yaml")]
         impl FromStr for $settings {
             type Err = String;
             fn from_str(s: &str) -> Result<Self, <Self as FromStr>::Err> {