`error!()` is too easily conflatable with `fail!()`

[bstrie]

Before they were both macros, the name of this log level was defensible:

// In days of yore...
log(error, "foo");
fail "foo";

Nowadays, this is a wart in the making:

// Rust Certification Exam, Question 22: how do these differ?
error!("foo");
fail!("foo");

The other log level macros (info, warn, and debug) are fine. I really don't care what we replace error with, though I propose alert! if nobody has any sublime suggestions.

[thestinger]

How about using log!(level, "message")?

[bstrie]

Making log into a macro (...again...) would solve our earlier problem of needing to have info, error, warn, and debug as pervasive constants. It would also allow people to use log to name their own variables, as so many people requested.

Assuming that error! is the most common macro, we could also simply make log!("foo") the same as log!(error, "foo").

[brson]

It's a wart yeah. Nominating.

[catamorphism]

Sub-bug of #3309. De-nominating

[flaper87]

Going back to log(level, msg) makes sense to me, I'm not sure about making log(msg) the same as log!(error, msg), I'd make info the default level instead. Thoughts?

[alexcrichton]

Nominating for backwards-compatible, error logging is something that while not used often should still be used occasionally.

[flaper87]

Actually, Thinking about this a bit further and looking at 20ab30fc583baeb87bb58bb369e97003a76a8a10 I think error! is fine and having the 4 of them makes more sense. What about changing fail! instead?

Some ideas: exit, die, raise

[alexcrichton]

After doing a bit of research on this, I disagree with renaming error! to anything else. The debug/info/warn/error log levels appear to be standard across pretty much all implementations/explanations that I could find:

• http://stackoverflow.com/questions/2031163/when-to-use-log-level-warn-vs-error
• http://docs.python.org/2/library/logging.html
• http://commons.apache.org/proper/commons-logging//apidocs/org/apache/commons/logging/Log.html#fatal%28java.lang.Object,%20java.lang.Throwable%29
• http://docs.racket-lang.org/reference/logging.html

And that was just for an immediate search of "error log level". If at all it seems that we're missing the fatal! and trace! log levels (although I'm not so sure about trace!).

In my opinion, the stackoverflow answer to what the log levels mean is a good summary of what each one is and specifically why error! shouldn't fail/die. I think that the fix for this issue should be better documentation about core macros rather than renaming them.

[catamorphism]

I agree with @alexcrichton . In the interest of avoiding gratuitous code churn, I'm closing this.