add -Zunpretty=hir-tree

[nikomatsakis]

This uses the debug impls to dump the raw HIR. Particularly useful when
learning how the compiler works.

cc @qmx

[rust-highfive]

r? @arielb1

(rust_highfive has picked a reviewer for you, use r? to override)

[qmx]

👍 useful

[nikomatsakis]

You can also do -Zdump-tree=22 to lower the contents of node-id 22, or -Zdump-tree=foo to lower a particular path foo. I've found the latter... imperfect... in my testing, but it's just using the existing infrastructure.

Er, I meant --unpretty=hir-tree=22 -Zunstable-options.

I'd really like to change --unpretty to -Zunpretty but this is enough for one day.

[arielb1]

Could you add a run-make test on some sort of "Hello World" program (an Hello World without println!, I suppose), just that we make sure this doesn't randomly break, or do you think that would be too much of a maintenance burden?

[nikomatsakis]

@arielb1 good question. It does seem useful to have a test -- but I am not super keen about periodically updating it with new HIR. I guess we could just check that it emits something non-empty or perhaps something with a few strings (e.g., names of the functions)?

[arielb1]

Sure, just running it, seeing that it doesn't crash, and seeing that e.g. a string literal from the code appears in the HIR should work.

[shepmaster]

Greetings from triage, @nikomatsakis! It's been a week since we last heard from you here — will you be able to add the requested tests sometime soon?

[nikomatsakis]

@shepmaster I will, I'm just slow. =)

[nikomatsakis]

Added a test.

[arielb1]

@bors r+

[bors]

📌 Commit 61f31fd has been approved by arielb1

[bors]

⌛ Testing commit 61f31fd with merge 2591df308e0af291feaf1161a7751f002bcd41da...

[kennytm]

@bors retry — prioritize #46183

[bors]

⌛ Testing commit 61f31fd with merge 6af4515...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: arielb1
Pushing 6af4515 to master...