Replace GUI exercise with Logger

[djmitche]

This should be a bit simpler, and notably

• does not require trait objects, which per "Trait Objects" require understanding of Box #1516 should be moved later in the course
• does not require a lot of futzing with string formatting

But all that hard work developing the GUI exercise is not for naught: it remains in the "Modules" segment, where students will get a chance to read some Rust code and reorganize it a little bit.

Fixes #1617.

R=mgeisler as the original author of the GUI exercise.

[djmitche]

dprint fmt on my system doesn't make any changes here. Any idea why it's failing in the PR and not locally?

[mgeisler]

Thanks, I like this a lot! It makes the generics part much more focused and it shows a useful pattern.

dprint fmt on my system doesn't make any changes here. Any idea why it's failing in the PR and not locally?

Not sure! I just tried it here:

% gh pr checkout 1682
remote: Enumerating objects: 17, done.
remote: Counting objects: 100% (17/17), done.
remote: Compressing objects: 100% (7/7), done.
remote: Total 17 (delta 10), reused 16 (delta 10), pack-reused 0
Unpacking objects: 100% (17/17), 3.73 KiB | 954.00 KiB/s, done.
From github.com:google/comprehensive-rust
 * [new ref]         refs/pull/1682/head -> issue1617
Switched to branch 'issue1617'
% dprint fmt
Formatted 1 file.
% git diff                                                           (~/src/comprehensive-rust)
diff --git a/src/modules/exercise.rs b/src/modules/exercise.rs
index 87bf452..09fbb19 100644
--- a/src/modules/exercise.rs
+++ b/src/modules/exercise.rs
@@ -84,8 +84,8 @@ impl Widget for Window {
 
         let inner_width = self.inner_width();
 
-        // TODO: Change draw_into to return Result<(), std::fmt::Error>. Then use the ?-operator
-        // here instead of .unwrap().
+        // TODO: Change draw_into to return Result<(), std::fmt::Error>. Then use the
+        // ?-operator here instead of .unwrap().
         writeln!(buffer, "+-{:-<inner_width$}-+", "").unwrap();
         writeln!(buffer, "| {:^inner_width$} |", &self.title).unwrap();
         writeln!(buffer, "+={:=<inner_width$}=+", "").unwrap();

Ah, I know why!

Wrapping of comments is an unstable rustfmt feature... We therefore run dprint fmt after a rustup default unstable in CI. I also see no output if I switch back to stable temporarily!

Let me try to fix this!

[mgeisler]

I found a way to run rustfmt from Rust nightly, assuming you have rustup on the system. Please see #1694.

[mgeisler]

Thanks a lot!