Introduce librustc_index crate

[csmoe]

Closes #50592

[rust-highfive]

r? @petrochenkov

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[csmoe]

r? @nikomatsakis

[csmoe]

@eddyb almost no changes here, https://github.com/rust-lang/rust/pull/64778/files#diff-1240c4024b5a96328bb0436c2344a020L847, but I cannot figure out where the error came from.

[eddyb]

Presumably rustdoc is using a different copy of the IndexVec type?

[csmoe]

r? @eddyb

[rust-highfive]

The job mingw-check of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-09-29T16:16:03.0765144Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-09-29T16:16:03.9308289Z ##[command]git config gc.auto 0
2019-09-29T16:16:03.9315403Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-09-29T16:16:03.9318231Z ##[command]git config --get-all http.proxy
2019-09-29T16:16:03.9325183Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/64778/merge:refs/remotes/pull/64778/merge
---
2019-09-29T16:25:56.4042948Z 
2019-09-29T16:25:57.5749384Z error[E0599]: no function or associated item named `new` found for type `rustc::mir::Local` in the current scope
2019-09-29T16:25:57.5750635Z    --> src/librustc_codegen_ssa/mir/block.rs:232:43
2019-09-29T16:25:57.5750916Z     |
2019-09-29T16:25:57.5751237Z 232 |             match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
2019-09-29T16:25:57.5751674Z     |                                           ^^^ function or associated item not found in `rustc::mir::Local`
2019-09-29T16:25:57.5752214Z     = help: items from traits can only be used if the trait is in scope
2019-09-29T16:25:57.5752214Z     = help: items from traits can only be used if the trait is in scope
2019-09-29T16:25:57.5752869Z     = note: the following trait is implemented but not in scope, perhaps add a `use` for it:
2019-09-29T16:25:57.5753114Z             `use rustc_index::vec::Idx;`
2019-09-29T16:25:58.9907442Z error: aborting due to 2 previous errors
2019-09-29T16:25:58.9910973Z 
2019-09-29T16:25:58.9922871Z Some errors have detailed explanations: E0432, E0599.
2019-09-29T16:25:58.9932416Z For more information about an error, try `rustc --explain E0432`.
---
2019-09-29T16:26:05.5367857Z == clock drift check ==
2019-09-29T16:26:05.5388208Z   local time: Sun Sep 29 16:26:05 UTC 2019
2019-09-29T16:26:05.7027017Z   network time: Sun, 29 Sep 2019 16:26:05 GMT
2019-09-29T16:26:05.7030562Z == end clock drift check ==
2019-09-29T16:26:07.0126898Z ##[error]Bash exited with code '1'.
2019-09-29T16:26:07.0164760Z ##[section]Starting: Checkout
2019-09-29T16:26:07.0166707Z ==============================================================================
2019-09-29T16:26:07.0166769Z Task         : Get sources
2019-09-29T16:26:07.0166831Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[eddyb]

cc @nikomatsakis

@bors r+

[bors]

📌 Commit 64f61c7 has been approved by eddyb

[bors]

⌛ Testing commit 64f61c7 with merge 22bc9e1...

[bors]

☀️ Test successful - checks-azure
Approved by: eddyb
Pushing 22bc9e1 to master...