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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.

@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.

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

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

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

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

@rfcbot fcp merge

Seems like a neat feature to me!

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.

@bors: r+

📌 Commit 7d6227a has been approved by alexcrichton

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

☀️ 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...

All relevant subteam members have reviewed. No concerns remain.

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