Use prettier arrow in stack traces (to highlight the line with the error)

[holly-cummins]

TLDR: the 'after'

EDIT: After testing on Windows, I've changed the arrow.

What problem were we solving?

In @phillip-kruger's recent demo of the advanced exception context, I noticed that we use an ascii-art arrow.

"Hmm," I thought. "With so many nice arrows in the unicode spec these days, why don't we use one of them instead?" With hindsight, I should have asked @phillip-kruger if he’d tried this already, but I thought “I won’t bother him with a conversation for a one-character change, I’ll just do the PR and we can discuss it there.” Then I started testing, and realised why Philip maybe opted for the ascii art. But by then it was too late, and I was invested.

There are two risks with this change:

• Will the character be available in the terminal and browser font on the developer's system?
• Can we make the code in the line with the arrow align properly with the rest?

It turns out both are a problem, but I think I got there in the end.

Cross-platform test results

MacOS

Windows

Linux

The workings-out

Character width issues

Even on a single machine, I got character-alignment problems. It turns out that fixed-width fonts do not have a consistent width for the arrows. It will presumably vary by OS, and it also varies between browser and terminal. I liked the heavy arrow ⮕, but that was subtly misaligned in the browser:

... and hopelessly misaligned in the terminal:

⟶ is nice and prominent, perfect in the console,

But terrible in the browser

In my experiments, ⇨ works in the browser:

and also the terminal

It's a bit more visible than ⇾, which also worked for me in terms of width:

Character set issues

Once I found an arrow that rendered well in both terminal and browser on Mac, we tried it on Windows, and ... no good.

So I went back to the drawing board.

How to test

Here's some text which can be pasted into a terminal to test on other OSes:

Exception in GreetingResource.java:14
          12      @Produces(MediaType.TEXT_PLAIN)
          13      public String hello() {
        ⇨ 14          if (Math.random( )> 0.01) { throw new RuntimeException("test");}
          15          return "Hello from Quarkus RESTyes";
          16      }

(Testing in the browser would need a build of the patch.)

Other options

For reference, here are all the arrows I considered, along with a . to show alignment. Only the fourth one works on Windows:

⟶ .
⭢ .
⮕ .
→ .
⇨ .
⇢ .
⇾ .

[phillip-kruger]

Very cool !! Thanks. I did not think of that at all :)

[gsmet]

TBH, while not pretty, I think the previous behavior was a bit more visible (at least for me and my bad eyes). But I won't fight it :).

Also, we need to check how it behaves on Windows (as it has been quite a pain when going non-ascii in the term).

[holly-cummins]

TBH, while not pretty, I think the previous behavior was a bit more visible (at least for me and my bad eyes). But I won't fight it :).

Yes, I agree it's a touch less visible now. I was sad that I couldn't get the width of the chunky arrow to work, since it was most visible.

Also, we need to check how it behaves on Windows (as it has been quite a pain when going non-ascii in the term).

100% I'm polling around a few developers who I think might have windows machines. :)

[holly-cummins]

@gastaldi has kindly tested on Windows, and concerns were justified:

[gastaldi]

Here is a screenshot in Edge (Windows 11):

[quarkus-bot]

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