test: Verify auto-traits for core types

By checking these types, we'll get some other types for free, like
`Command` verifying `Arg`.

This was inspired by #3876

Cargo.toml

@@ -114,6 +114,7 @@ trycmd = { version = "0.13", default-features = false, features = ["color-auto",
 humantime = "2"
 snapbox = "0.2.9"
 shlex = "1.1.0"
+static_assertions = "1.1.0"
 
 [[example]]
 name = "demo"

src/builder/command.rs

@@ -5107,3 +5107,8 @@ where
         _ => None,
     }
 }
+
+#[test]
+fn check_auto_traits() {
+    static_assertions::assert_impl_all!(Command: Send, Sync, Unpin);
+}

src/error/mod.rs

@@ -1147,12 +1147,7 @@ impl Display for Backtrace {
     }
 }
 
-#[cfg(test)]
-mod tests {
-    /// Check `clap::Error` impls Send and Sync.
-    mod clap_error_impl_send_sync {
-        use crate::Error;
-        trait Foo: std::error::Error + Send + Sync + 'static {}
-        impl Foo for Error {}
-    }
+#[test]
+fn check_auto_traits() {
+    static_assertions::assert_impl_all!(Error: Send, Sync, Unpin);
 }

src/parser/error.rs

@@ -54,3 +54,14 @@ impl std::fmt::Display for MatchesError {
         }
     }
 }
+
+#[test]
+fn check_auto_traits() {
+    static_assertions::assert_impl_all!(
+        MatchesError: Send,
+        Sync,
+        std::panic::RefUnwindSafe,
+        std::panic::UnwindSafe,
+        Unpin
+    );
+}

src/parser/matches/arg_matches.rs

@@ -1741,6 +1741,11 @@ fn unwrap_os_string_arg<'v>(id: &Id, value: &'v AnyValue) -> &'v OsStr {
 mod tests {
     use super::*;
 
+    #[test]
+    fn check_auto_traits() {
+        static_assertions::assert_impl_all!(ArgMatches: Send, Sync, Unpin);
+    }
+
     #[test]
     fn test_default_values() {
         #![allow(deprecated)]

tests/derive_ui/next/tuple_struct.stderr

@@ -17,5 +17,5 @@ error[E0599]: no function or associated item named `parse` found for struct `Opt
    |
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following traits define an item `parse`, perhaps you need to implement one of them:
-           candidate #1: `StructOpt`
+           candidate #1: `Parser`
            candidate #2: `TypedValueParser`