Improve "Doesn't live long enough" error

[mikhail-m1]

case with temporary variable

issue #36279 part of #35233

r? @jonathandturner

[sophiajt]

Hmm, this doesn't look quite right. It looks like we're getting rid of the temporary value message altogether. Instead, I think we want to use the same style of fixed we used before.

For example, instead of this:

error: borrowed value does not live long enough
  --> <anon>:11:17
   |
11 |     for line in std::io::stdin().lock().lines().map(|l| l.unwrap()) {
   |                 ^^^^^^^^^^^^^^^^ temporary value created here
...
18 |     }
   |     - temporary value dropped before borrower
   |
   = note: values in a scope are dropped in the opposite order they are created

Have this:

error: borrowed value does not live long enough
  --> <anon>:11:17
   |
11 |     for line in std::io::stdin().lock().lines().map(|l| l.unwrap()) {
   |                 ---------------- temporary value created here
...
18 |     }
   |     ^ temporary value dropped before borrower
   |
   = note: values in a scope are dropped in the opposite order they are created

[sophiajt]

Though I noticed that sometimes we don't put the error on the last one. Like this example:

error: `r` does not live long enough
  --> <anon>:21:9
   |
18 |     r.listen(Box::new(|| {
   |                       -- capture occurs here
...
21 |         r.something();
   |         ^ does not live long enough
22 |     }));
23 | }
   | - borrowed value dropped before borrower

Still, I think with the temporary value, the fix I'm showing reads okay

[mikhail-m1]

@jonathandturner I did not noticed the loss of 'temporary' in error. It's easy to fix. But I reread #36279, is it about split temporary and local variables? And was it already completed?
I could rework case with closure, just give me required output.

[sophiajt]

@mikhail-m1 - I think that's an older error before we made the message wording better for temporaries.

I think the only step left for temporaries is to switch which is primary and which is secondary.

[alexcrichton]

@jonathandturner does the most recent iteration look good to you?

[sophiajt]

Looks good!

@bors r+ rollup

[bors]

📌 Commit cfdf763 has been approved by jonathandturner

[bors]

⌛ Testing commit cfdf763 with merge acce384...

[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: jonathandturner
Pushing acce384 to master...