lint: deny incoherent_fundamental_impls by default

[hdhoang]

Warn the ecosystem of the pending intent-to-disallow in #49799.

There are 4 ICEs on my machine, look unrelated (having happened before in #49146 (comment))

thread 'main' panicked at 'assertion failed: position <= slice.len()', libserialize/leb128.rs:97:1

    [run-pass] run-pass/allocator/xcrate-use2.rs
    [run-pass] run-pass/issue-12133-3.rs
    [run-pass] run-pass/issue-32518.rs
    [run-pass] run-pass/trait-default-method-xc-2.rs

r? @nikomatsakis

[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.

[00:50:25] ............................................................................ii......................
[00:51:12] ........................................i....................................................i.ii...
[00:51:23] ............................test [run-pass] run-pass/saturating-float-casts.rs has been running for over 60 seconds
[00:51:51] ........................................................................
[00:52:13] .iiiiiii............................................................................................
[00:52:52] ....................................................................................................
[00:53:09] ..........................................................................
[00:53:09] test result: ok. 2955 passed; 0 failed; 19 ignored; 0 measured; 0 filtered out
[00:53:09] 
---
[01:25:31] 
[01:25:31] failures:
[01:25:31] 
[01:25:31] ---- /checkout/src/doc/rustc/src/lints/listing/warn-by-default.md - Warn_by_default_lints::incoherent_fundamental_impls (line 125) stdout ----
[01:25:31]  error: conflicting implementations of trait `main::Trait1<std::boxed::Box<_>>` for type `main::A`: (E0119)
[01:25:31]   --> /checkout/src/doc/rustc/src/lints/listing/warn-by-default.md:138:1
[01:25:31]    |
[01:25:31] 11 | impl<X, T> Trait1<X> for T where T: Trait2<X> {
[01:25:31]    | --------------------------------------------- first implementation here
[01:25:31] ...
[01:25:31] 15 | impl<X> Trait1<Box<X>> for A {
[01:25:31]    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `main::A`
[01:25:31]    |
[01:25:31]    = note: #[deny(incoherent_fundamental_impls)] on by default
[01:25:31]    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
[01:25:31]    = note: for more information, see issue #46205 <https://github.com/rust-lang/rust/issues/46205>
[01:25:31]    = note: downstream crates may implement trait `main::Trait2<std::boxed::Box<_>>` for type `main::A`
[01:25:31] thread '/checkout/src/doc/rustc/src/lints/listing/warn-by-default.md - Warn_by_default_lints::incoherent_fundamental_impls (line 125)' panicked at 'couldn't compile the test', librustdoc/test.rs:321:13
[01:25:31] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:25:31] 
[01:25:31] 
---
[01:25:31] 
[01:25:31] 
[01:25:31] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:25:31] Build completed unsuccessfully in 0:45:28
[01:25:31] Makefile:58: recipe for target 'check' failed
[01:25:31] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:03aa0ab0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

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)

[hdhoang]

looks like I need to coordinate with the src/doc submodule. How should I go about that?

[nikomatsakis]

@hdhoang I think you can just edit this file directly:

https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/lints/listing/warn-by-default.md

Presumably just move the relevant entry to

https://github.com/rust-lang/rust/blob/master/src/doc/rustc/src/lints/listing/deny-by-default.md

[hdhoang]

Oh, how did I come to think doc was a submodule. I have updated the listings.

#49799 happened before doc/rustc came in, so I'll edit the lists again when merging this PR in via master.

[shepmaster]

Ping from triage, @nikomatsakis — looks like this is back in your court!

[nikomatsakis]

@bors r+

[bors]

📌 Commit cabbe50 has been approved by nikomatsakis

[nikomatsakis]

Thanks @hdhoang !

[bors]

⌛ Testing commit cabbe50 with merge 295d980...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 295d980 to master...