I didn't find any duplicate issue, but this problem has probably been there for a long time.

• The code panic!("{}", 7) compiles and prints thread <main> panicked at "7", ...
• The code panic!("{} {}", 7) doesn't compile as an argument is missing
• The code panic!("{}") does compile and prints thread <main> panicked at "{}", ...

The last one doesn't detect potential mistakes, and is inconsistent with println!("{}") which doesn't compile.