resolve: Extern prelude is for type namespace only

[petrochenkov]

Fixes#56263 (stable-to-beta regression)

[rust-highfive]

r? @matthewjasper

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[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.

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travis_time:end:0d006fe3:start=1543278764668816830,finish=1543278765752897792,duration=1084080962
$ 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
---
[00:16:33] Compiling rustc_plugin v0.0.0 (/checkout/src/librustc_plugin)
[00:16:35] error[E0308]: match arms have incompatible types
[00:16:35] --> src/librustc_resolve/resolve_imports.rs:163:22
[00:16:35] |
[00:16:35] 163 | let module = match module {
[00:16:35] | ______________________^
[00:16:35] 164 | | ModuleOrUniformRoot::Module(module) => module,
[00:16:35] 165 | | ModuleOrUniformRoot::UniformRoot(uniform_root_kind) => {
[00:16:35] 166 | | assert!(!restricted_shadowing);
[00:16:35] 206 | | }
[00:16:35] 207 | | };
[00:16:35] | |_________^ expected reference, found enum `std::result::Result`
[00:16:35] |
[00:16:35] |
[00:16:35] = note: expected type `&ModuleData<'_>`
[00:16:35] found type `std::result::Result<&NameBinding<'_>, (syntax::ext::base::Determinacy, Weak)>`
[00:16:35] note: match arm with an incompatible type
[00:16:35] --> src/librustc_resolve/resolve_imports.rs:165:68
[00:16:35] |
[00:16:35] 165 | ModuleOrUniformRoot::UniformRoot(uniform_root_kind) => {
[00:16:35] | ____________________________________________________________________^
[00:16:35] 166 | | assert!(!restricted_shadowing);
[00:16:35] 167 | | match uniform_root_kind {
[00:16:35] 168 | | UniformRootKind::ExternPrelude => {
[00:16:35] 205 | | }
[00:16:35] 206 | | }
[00:16:35] | |_____________^
[00:16:35] 

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[bors]

☔ The latest upstream changes (presumably #56262) made this pull request unmergeable. Please resolve the merge conflicts.

[nikomatsakis]

@bors r+ p=1

[bors]

📌 Commit cd2e98d has been approved by nikomatsakis

[nikomatsakis]

cc @rust-lang/compiler

Accepting for beta backport because (a) it's simple and (b) have to move quick as this is a Rust 2018 regression.

[bors]

⌛ Testing commit cd2e98d with merge 400c2bc...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 400c2bc to master...

[nikomatsakis]

Removing beta-accepted so we can discuss in today's @rust-lang/compiler meeting.

[pnkfelix]

discussed in T-compiler meeting. beta-accepted.