Restrict scope of automatic usage hint in standard error writer, so the default behaviour is less spammy

jaarg/src/help.rs

@@ -209,19 +209,22 @@ impl<ID> core::fmt::Display for StandardErrorUsageWriter<'_, ID> {
     // Write error
     writeln!(f, "{name}: {error}", name=self.0.program_name, error = self.0.error)?;
 
-    // Write usage
+    // Provide usage hint for missing required arguments
+    if matches!(self.0.error, ParseError::RequiredPositional(_) | ParseError::RequiredParameter(_)) {
+      // Write short usage
       writeln!(f, "{}", StandardShortUsageWriter::new(HelpWriterContext {
         options: self.0.options,
         program_name: self.0.program_name
       }))?;
 
-    // Write full help instruction if a
+      // Write full help instruction if available
       if let Some(help_option) = self.0.options.help_option() {
         writeln!(f, "Run '{name} {help}' to view all available options.",
           name = self.0.program_name,
           // Prefer long name, but otherwise any name is fine
           help = help_option.first_long_name().unwrap_or(help_option.first_name()))?;
       }
+    }
     Ok(())
   }
 }