[slf4j-user] Inconsistent behavior introduced in SLF4J version 1.7.15

[Daniel Trebbien]

Hello,

I have noticed an inconsistency in behavior of the following logging code:

    final Throwable t = new RuntimeException("some runtime exception");
    LOGGER.info("{} {} {}", new Object[] { "abc", "def", t });
    LOGGER.info("{} {}", "abc", t);
    LOGGER.info("{}", (Object) t);

In SLF4J versions 1.7.14 and earlier (tested 1.7.14, 1.7.13, 1.7.10, 1.7.7,
1.7.0, and 1.6.0), the result using the "simple" backend is:

[main] INFO test.Main - abc def java.lang.RuntimeException: some runtime
exception
[main] INFO test.Main - abc java.lang.RuntimeException: some runtime
exception
[main] INFO test.Main - java.lang.RuntimeException: some runtime exception

In SLF4J versions 1.7.15 and newer (tested 1.7.15 and 1.7.25), the result
is:

[main] INFO test.Main - abc def {}
java.lang.RuntimeException: some runtime exception
at test.Main.main(Main.java:10)
[main] INFO test.Main - abc {}
java.lang.RuntimeException: some runtime exception
at test.Main.main(Main.java:10)
[main] INFO test.Main - java.lang.RuntimeException: some runtime exception


To me, the new behavior is unexpected, and it is inconsistent with the
logging variant taking exactly one parameter because although the Throwable
instance is the last parameter, the one and only formatting anchor in the
format string is replaced by the toString() result and the stack trace is
not logged.

Is this a bug?

Daniel Trebbien
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