[WIP] Make 2PB reservations conflict with shared borrows

[matthewjasper]

Putting this up for discussion.

r? @nikomatsakis

[rust-highfive]

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (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.

travis_time:end:18769107:start=1543361681520406826,finish=1543361682652815024,duration=1132408198
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#Pull-Requests-and-Security-Restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-5.0
---
[00:23:33]    Compiling proc_macro v0.0.0 (/checkout/src/libproc_macro)
[00:23:42]    Compiling syntax_ext v0.0.0 (/checkout/src/libsyntax_ext)
[00:30:28]    Compiling rustc_mir v0.0.0 (/checkout/src/librustc_mir)
[00:30:28]    Compiling rustc_typeck v0.0.0 (/checkout/src/librustc_typeck)
[00:31:40] error[E0502]: cannot borrow `block_data.statements` as mutable because it is also borrowed as immutable
[00:31:40]    --> src/librustc_mir/transform/add_retag.rs:185:29
[00:31:40]     |
[00:31:40] 167 |                 match block_data.statements[i].kind {
[00:31:40] ...
[00:31:40] ...
[00:31:40] 185 |                             block_data.statements.insert(i, Statement {
[00:31:40] 186 |                                 source_info,
[00:31:40] 186 |                                 source_info,
[00:31:40] 187 |                                 kind: StatementKind::EscapeToRaw(src.clone()),
[00:31:40]     |                                                                  --- immutable borrow used here, in later iteration of loop
[00:31:40] 
[00:31:40] error[E0502]: cannot borrow `block_data.statements` as mutable because it is also borrowed as immutable
[00:31:40]    --> src/librustc_mir/transform/add_retag.rs:197:25
[00:31:40]     |
[00:31:40] 167 |                 match block_data.statements[i].kind {
[00:31:40] ...
[00:31:40] ...
[00:31:40] 197 |                         block_data.statements.insert(i+1, Statement {
[00:31:40] 198 |                             source_info,
[00:31:40] 198 |                             source_info,
[00:31:40] 199 |                             kind: StatementKind::Retag { fn_entry: false, place: place.clone() },
[00:31:40]     |                                                                                  ----- immutable borrow used here, in later iteration of loop
[00:31:48] error: aborting due to 2 previous errors
[00:31:48] 
[00:31:48] For more information about this error, try `rustc --explain E0502`.
[00:31:48] error: Could not compile `rustc_mir`.
[00:31:48] error: Could not compile `rustc_mir`.
[00:31:48] warning: build failed, waiting for other jobs to finish...
[00:32:46] error: build failed
[00:32:46] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "--message-format" "json"
[00:32:46] expected success, got: exit code: 101
[00:32:46] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:32:46] Build completed unsuccessfully in 0:29:23
[00:32:46] Makefile:28: recipe for target 'all' failed
[00:32:46] make: *** [all] Error 1
35580 ./.git/modules/src/libcompiler_builtins/modules/compiler-rt/objects
35572 ./.git/modules/src/libcompiler_builtins/modules/compiler-rt/objects/pack
34948 ./src/llvm/test/tools
33444 ./obj/build/x86_64-unknown-linux-gnu/stage0-std

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)

[pnkfelix]

cc #56254

[pietroalbini]

@bors try

[bors]

⌛ Trying commit 3908328e3066dc1fd52f3e49a2a868ff30dbf32e with merge 096db501f6baee6fe429975a0e15765891c33e70...

[bors]

💔 Test failed - status-travis

[matthewjasper]

We're not backporting this.