add println!() macro with out any arguments

[sbwtw]

lets add println!() to write "\n".
like java https://docs.oracle.com/javase/7/docs/api/java/io/PrintStream.html#println()

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[alexcrichton]

Thanks for the PR! This seems like a reasonable feature to me, especially given that we've got panic!(). Looks like the failures on travis though are legitimate.

[bluss]

@sbwtw It looks like these two tests failed due to the changes:

failures:
    [compile-fail] compile-fail/empty-comment.rs
    [compile-fail] compile-fail/issue-7970a.rs

You can find them inside src/test in the rust source tree. Both are using println!() and expecting it to fail. I suggest you in both test cases simply define a new macro that uses at least one argument, and use that macro instead of println.

[sbwtw]

@bluss @alexcrichton hi, I have modified the test code.

[sinkuu]

What about letting writeln!(dst) to also write \n?

[sbwtw]

@sinkuu seems good, but I think its better to modify it in another commit.

[alexcrichton]

Thanks @sbwtw! This is tagged with T-libs so we'll get around to discussing this in triage next week hopefully.

[alexcrichton]

@rfcbot fcp merge

Seems like a neat feature to me!

[rfcbot]

FCP proposed with disposition to merge. Review requested from:

• @BurntSushi
• @Kimundi
• @alexcrichton
• @aturon
• @brson
• @sfackler

No concerns currently listed.
See this document for info about what commands tagged team members can give me.

[alexcrichton]

@bors: r+

[bors]

📌 Commit 7d6227a has been approved by alexcrichton

[bors]

⌛ Testing commit 7d6227a with merge 1e4c8b1...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-rustbuild
Approved by: alexcrichton
Pushing 1e4c8b1 to master...

[rfcbot]

All relevant subteam members have reviewed. No concerns remain.

[rfcbot]

It has been one week since all blocks to the FCP were resolved.