Allow to mark arguments as to be ignored by suggestions.

As pointed out in clap-rs#4853, it might be useful to mark arguments to not be
considered by the suggestions feature.

In particular with the introduction of UnknownArgumentValueParser in clap-rs#5075,
one might want explicitly handle some common confusion (say handle
`--silent` and print `tip: did you mean --quiet`), but not have those in
the suggestion engine. I'm guessing one might want to have an `arg` be visible
but not in suggestion for deprecated flags as well.

I'm trying to do so by adding a `.didyoumena(false)`, that will mark the
argument as to not be considered by suggestion.

There is also some mention of completion of hidden command in clap-rs#4853,
that might be relevant as well.

--

I'm not too familiar with clap internals, and fairly new to rust,
but in particular :

 - I've tried to implement that only for args - I guess we will need to
   extend to subcommands if this goes further
 - I'm not happy with the setting negations nor the naming
   `didyoumean`/`ExcludeDidYouMean`
 - I'm not super happy about the iteration over MKeyMap keys and items.

clap_builder/src/builder/arg.rs

@@ -2349,6 +2349,46 @@ impl Arg {
         }
     }
 
+    /// Do not include the argument in didyoumean suggestions.
+    ///
+    /// # Examples
+    ///
+    /// Setting `ExcludeDidYouMean` will not consider the argument
+    /// when making suggestions for mistyped arguments.
+    ///
+    /// ```rust
+    /// # use clap_builder as clap;
+    /// # use clap::{Command, Arg};
+    /// let m = Command::new("prog")
+    ///     .arg(Arg::new("cfg")
+    ///         .long("config")
+    ///         .didyoumean(false)
+    ///     .get_matches_from(vec![
+    ///         "prog", "--conf"
+    ///     ]);
+    /// # }
+    /// ```
+    ///
+    /// The above example will not display the usual `a similar argument  ...`
+    /// message
+    ///
+    /// ```text
+    /// error: unexpected argument '--conf' found
+    ///
+    /// Usage: prog [OPTIONS]
+    ///
+    /// For more information, try '--help'.
+    /// ```
+    #[inline]
+    #[must_use]
+    pub fn didyoumean(self, yes: bool) -> Self {
+        if yes {
+            self.unset_setting(ArgSettings::ExcludeDidYouMean)
+        } else {
+            self.setting(ArgSettings::ExcludeDidYouMean)
+        }
+    }
+
     /// Do not display the [possible values][crate::builder::ValueParser::possible_values] in the help message.
     ///
     /// This is useful for args with many values, or ones which are explained elsewhere in the
@@ -4153,6 +4193,11 @@ impl Arg {
         self.is_set(ArgSettings::HideEnv)
     }
 
+    /// dont did you mean
+    pub fn is_didyoumean_set(&self) -> bool {
+        !self.is_set(ArgSettings::ExcludeDidYouMean)
+    }
+
     /// Report whether [`Arg::hide_env_values`] is set
     #[cfg(feature = "env")]
     pub fn is_hide_env_values_set(&self) -> bool {

clap_builder/src/builder/arg_settings.rs

@@ -61,6 +61,7 @@ pub(crate) enum ArgSettings {
     HiddenShortHelp,
     HiddenLongHelp,
     Exclusive,
+    ExcludeDidYouMean,
 }
 
 impl ArgSettings {

clap_builder/src/parser/parser.rs

@@ -1503,13 +1503,21 @@ impl<'cmd> Parser<'cmd> {
     ) -> ClapError {
         debug!("Parser::did_you_mean_error: arg={arg}");
         // Didn't match a flag or option
-        let longs = self
-            .cmd
-            .get_keymap()
+        let keymap = self.cmd.get_keymap();
+        let longs = keymap
             .keys()
-            .filter_map(|x| match x {
-                KeyType::Long(l) => Some(l.to_string_lossy().into_owned()),
-                _ => None,
+            .filter_map(|key| {
+                let arg = keymap.get(key)?;
+                match (key, arg) {
+                    (KeyType::Long(l), arg) => {
+                        if arg.is_didyoumean_set() {
+                            Some(l.to_string_lossy().into_owned())
+                        } else {
+                            None
+                        }
+                    }
+                    (_, _) => None,
+                }
             })
             .collect::<Vec<_>>();
         debug!("Parser::did_you_mean_error: longs={longs:?}");

tests/builder/opts.rs

@@ -458,6 +458,22 @@ For more information, try '--help'.
     utils::assert_output(utils::complex_app(), "clap-test --optio=foo", DYM, true);
 }
 
+#[test]
+#[cfg(feature = "suggestions")]
+#[cfg(feature = "error-context")]
+fn did_you_mean_disabled() {
+    static DYM: &str = "\
+error: unexpected argument '--conf' found
+
+Usage: clap-test [OPTIONS]
+
+For more information, try '--help'.
+";
+
+    let c = Command::new("clap-test").arg(Arg::new("cfg").long("config").didyoumean(false));
+    utils::assert_output(c, "clap-test --conf", DYM, true);
+}
+
 #[test]
 fn issue_1047_min_zero_vals_default_val() {
     let m = Command::new("foo")