[WIP] add check if lints belong to an external macro

[Dylan-DPC-zz]

Closes #48855

r? @Manishearth

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Manishearth (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[Manishearth]

Alright, this is a good first step -- now, the LintStore contains a hashmap of future incompatibility lints; we should always lint for these, regardless of the macro. So check the lint id against that.

[pietroalbini]

Ping from triage @Dylan-DPC! The reviewer requested some changes, could you implement them in the near future?

[Dylan-DPC-zz]

Yes sure. Will add them in a few days 👍

[Dylan-DPC-zz]

@Manishearth I don't have access to the LintStore in the place where i'm checking the lint. Any clues?

[pietroalbini]

Ping from triage @Manishearth! The author needs a bit of help.

[Manishearth]

Sure you do -- .lints()

[shepmaster]

Ping from triage, @Dylan-DPC ! You have test failures to address.

[rust-highfive]

The job x86_64-gnu-llvm-3.9 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.

[00:07:40]    Compiling syntax_ext v0.0.0 (file:///checkout/src/libsyntax_ext)
[00:07:42] error[E0432]: unresolved import `codemap`
[00:07:42]   --> librustc/lint/mod.rs:57:5
[00:07:42]    |
[00:07:42] 57 | use codemap::{ExpnFormat, ExpnInfo, Span };
[00:07:42]    |     ^^^^^^^ Did you mean `syntax::codemap`?
[00:07:45] error: unused import: `Span`
[00:07:45]   --> librustc/lint/mod.rs:57:37
[00:07:45]    |
[00:07:45]    |
[00:07:45] 57 | use codemap::{ExpnFormat, ExpnInfo, Span };
[00:07:45]    |
[00:07:45]    = note: `-D unused-imports` implied by `-D warnings`
[00:07:45] 
[00:07:58] error[E0308]: mismatched types
[00:07:58] error[E0308]: mismatched types
[00:07:58]    --> librustc/lint/context.rs:472:51
[00:07:58]     |
[00:07:58] 472 |                 if !lint::in_external_macro(lint, span) {
[00:07:58]     |                                                   ^^^^ expected struct `syntax_pos::Span`, found type parameter
[00:07:58]     = note: expected type `syntax_pos::Span`
[00:07:58]                found type `S`
[00:07:58] 
[00:07:58] 
[00:07:58] error[E0277]: the trait bound `lint::Lint: lint::context::LintContext<'_>` is not satisfied
[00:07:58]     |
[00:07:58]     |
[00:07:58] 472 |                 if !lint::in_external_macro(lint, span) {
[00:07:58]     |                     ^^^^^^^^^^^^^^^^^^^^^^^ the trait `lint::context::LintContext<'_>` is not implemented for `lint::Lint`
[00:07:58]     |
[00:07:58] note: required by `lint::in_external_macro`
[00:07:58]    --> librustc/lint/mod.rs:625:1
[00:07:58]     |
[00:07:58] 625 | pub fn in_external_macro<'a, T: LintContext<'a>>(cx: &T, span: Span) -> bool {
[00:07:58] 
[00:07:58] 
-rustc/x86_64-unknown-linux-gnu/release/deps/libserialize-946eff7380f27f57.rlib --extern rustc_apfloat=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/librustc_apfloat-b7c66a9cab3ff5a6.rlib --extern proc_macro=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/libproc_macro-8d928be2ff984c7f.so --extern log=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/liblog-4f0866e958f59455.rlib --extern rustc_errors=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/librustc_errors-b789a86e1ab64d11.so -L native=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/build/backtrace-sys-31a3817325787acc/out/.libs -L native=/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/build/miniz-sys-90c24e5cae9d047e/out` (exit code: 101)
[00:08:11] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "--release" "--locked" "--color" "always" "--features" " jemalloc" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "--message-format" "json"
[00:08:11] expected success, got: exit code: 101
[00:08:11] thread 'main' panicked at 'cargo must succeed', bootstrap/compile.rs:1091:9
[00:08:11] travis_fold:end:stage0-rustc

[00:08:11] travis_time:end:stage0-rustc:start=1525535135554418716,finish=1525535323351964844,duration=187797546128
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[pietroalbini]

Ping from triage @Dylan-DPC! You have other failures to address.

[pietroalbini]

Thank you for this PR @Dylan-DPC! Unfortunately we haven't heard from you on this in a while, so I'm closing the PR to keep things tidy. Don't worry though, if you'll have time again in the future please reopen this PR, we'll be happy to review it again!

[Dylan-DPC-zz]

Oops sorry, got busy and demotivated to complete this. Sure no problems 😄