Use Unicode line drawing characters for spans

[kmcallister]

See discussion on old PR #21406. @Manishearth expressed interest in reviving this.

[sinistersnare]

+1 sounds nice.

Would this work on any windows terminals, such as the shell that comes with mingw?

Oh just read through the thread again, WGL4. cool!

[liigo]

Always prefer ASCII characters.

[tbelaire]

The plan, from before was to have both a flag --output-plain-ascii, as well as environment variables which can be set to always, auto or never, for each of color, having underlines at all, and having unicode underlines.

[ftxqxd]

Alternatively, we could use U+203E OVERLINE (‾, also part of WGL4) to create a simpler underline effect:

This is different from using an ANSI escape code such as \x1b[4m because it allows the underline colour to be different from the text’s colour.

[shinglyu]

I'm a noob, can I give it a try? I could try writing a unicode version, then implement the --output-plain-ascii flag.

[Manishearth]

@shinglyu sure! You can borrow a lot of stuff from Keegan's impl here, feel free to ask me if you have more questions!

[shinglyu]

@Manishearth : nice to see you again :)

[shinglyu]

@Manishearth : I tried to read the patch #21406, but I had a hard time understanding the codebase. Is there any document/blog post/diagram/etc that explains the folder structure and runtime behavior? Most of the docs I found are explaining the Rust language syntax.

Or should I start by reading the llvm tutorial?

[Manishearth]

src/librustc/session/config.rs contains the stuff for sorting out command line arguments

src/libsyntax/diagnostic.rs has the stuff for printing out a span.

You don't need to understand the rest at this stage, really :)

[shinglyu]

@Manishearth : thanks! I'll take a look.

[shinglyu]

@Manishearth @kmcallister : Changing ascii to UTF-8 is pretty straight forward. But I want to clarify the spec.

From what I understand in the closed PR,

• We have 3 environment variables for output capability
  • RUSTC_OUTPUT_COLOR = always | auto | never
  • RUSTC_OUTPUT_CURSOR_POS = always | auto | never
  • RUSTC_OUTPUT_UTF8 = always | auto | never
  • If any of the three is un-set or is invalid value, use auto
• There are 2 way to set the above three as never:
  • --output-plain-ascii flag
  • RUSTC_OUTPUT_PLAIN_ASCII =

I have some questions:

• If cursor positioning is not enabled, what do we do?
• What are all those flag stability and warning thing?

Thanks!