Implement ? in catch expressions

[cramertj]

Builds on #39921. Final part of #39849.

r? @nikomatsakis

[bors]

☔ The latest upstream changes (presumably #40133) made this pull request unmergeable. Please resolve the merge conflicts.

[nikomatsakis]

at first read, this all looks good, I'll have to revisit it in more detail when it's rebased

[nikomatsakis]

Ah, a thought. It'd be good to have some tests targeting the CFG etc. The idea would be to have initializations and moves that occur during a catch and check that we track it properly. For example:

let x;let _v = do catch{
x = 5;Ok(());};println!("{}", x);// OK

let x;let _v = do catch{
x = Ok(5)?;Ok(());};println!("{}", x);// ERROR

and similar tests for moves that may or may not occur (and perhaps a few for borrows that start in the catch and extend outside, etc).

[bors]

☔ The latest upstream changes (presumably #40220) made this pull request unmergeable. Please resolve the merge conflicts.

[nikomatsakis]

can you add a comment on this test explaining what the test aims to demonstrate (e.g., that a borrowed valid inside the do catch will propagate out?

I also think it'd be good to possibly break this test into distinct files.

[nikomatsakis]

can you modify the test to demonstrate that cfg_resis usable *within the do catch, if not outside?

Also, add a (run-pass) test like so, where cfg_res is initialized before the ?:

pubfnmain(){let cfg_res;let _:Result<(),()> = do catch{
cfg_res = 5;Err(())?;Ok(())};use(cfg_res);// OK}

[nikomatsakis]

I think I would also like some tests around lifetimes like these:

// Test that a borrow which only conditionally occurs still freezes `i` fnmain(){letmut i = 222;let j;let x = do catch{Err(())?;Ok(&i)};
i = 0;// ERRORprintln!("{}", i);}

// Test that a borrow which only conditionally occurs still freezes `i` fnmain(){letmut i = 222;let j;let x = do catch{Err(())?;
j = &i;Ok(())};
i = 0;// ERROR, I ... guess ... maybe not with NLLprintln!("{}", i);}

[nikomatsakis]

@bors r+

[bors]

📌 Commit bc07fe6 has been approved by nikomatsakis

[bors]

☔ The latest upstream changes (presumably #40598) made this pull request unmergeable. Please resolve the merge conflicts.

[nikomatsakis]

@bors r+

[bors]

📌 Commit 1f43731 has been approved by nikomatsakis

[bors]

⌛ Testing commit 1f43731 with merge 58c701f...