ADDITIONAL SYSTEM INFORMATION :
$ uname -a
Linux aquarius 4.19.0-17-amd64 #1 SMP Debian 4.19.194-2 (2021-06-21) x86_64 GNU/Linux
$ java -version
openjdk version "17" 2021-09-14
OpenJDK Runtime Environment Temurin-17+35 (build 17+35)
OpenJDK 64-Bit Server VM Temurin-17+35 (build 17+35, mixed mode, sharing)


A DESCRIPTION OF THE PROBLEM :
When a java.util.Formatter format string contains %t, but the corresponding argument is not a valid temporal type, the resulting IllegalFormatConversionException has a misleading message. The message does not mention the 't' conversion character at all; instead, only the character following the 't' is in the message.

For example, this:

new Formatter().format("%tc", "dummy");

...produces this exception:

java.util.IllegalFormatConversionException: c != java.lang.String

Of course, the conversion mismatch has nothing to do with the use of 'c'. The message should read:

java.util.IllegalFormatConversionException: t != java.lang.String


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Pass an argument which is neither Long, Date, Calendar, nor TemporalAccessor, along with a format string containing "%t", to a Formatter.format method.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The resulting exception should indicate that the argument is not suitable for a %t conversion.
ACTUAL -
The resulting exception implies that a different conversion character was the problem.

---------- BEGIN SOURCE ----------
import java.util.Formatter;

public class FormatterInvalidArgTest {
    public static void main(String[] args) {
        new Formatter().format("%tc", "dummy");
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Become accustomed to recognizing that "c != <type>" may refer to %tc (and extend that to all date-time conversions).

FREQUENCY : always