These migration lints aren't all up to par in terms of a good migration
experience. Some, like `unreachable_pub`, hit bugs like #52665 and unprepared
macros to be handled enough of the time. Others like linting against
`#[macro_use]` are swimming upstream in an ecosystem that's not quite ready (and
slightly buggy pending a few current PRs).
The general idea is that we will continue to recommend the `rust_2018_idioms`
lint group as part of the transition guide (as an optional step) but we'll be
much more selective about which lints make it into this group. Only those with a
strong track record of not causing too much churn will make the cut.
cc #52679
* Enable the `raw_identifiers` feature automatically in the 2018 preview
* Only emit lint warnings if the `raw_identifiers` feature is activated
cc rust-lang/cargo#5783
This commit adds a lint to the compiler to warn against the `#[macro_use]`
directive as part of the `rust_2018_idioms` lint. This lint is turned off by
default and is only enabled when the `use_extern_macros` feature is also
enabled.
The lint here isn't fully fleshed out as it's just a simple warning rather than
suggestions of how to actually import the macro, but hopefully it's a good base
to start from!
cc #52043
Background:
The anonymous lifetime mode is used to prohibit elided lifetimes where
they didn't used to be permitted, and instead require that `'_` be
used. For example:
```rust
impl Trait for Ref<T> { .. }
// ^^^^^^ ERROR: should be `Ref<'_, T>`
```
When we are parsing the parts of the impl header, we enter into an
alternate mode called `CreateParameter`. In this mode, we give an
error for things like `Ref<T>`, but for elided lifetimes in a
reference type like `&T` we make the elided lifetime into an in-band
lifetime:
4f99f37b7e/src/librustc/hir/lowering.rs (L4017-L4035)
This was not intended to change behavior because we only enter into
that mode in contexts where elision was not historically
permitted. However, the problem is that we fail to reset the mode when
we enter into bounds like `Fn(&u32)`, where elision *was* allowed --
the same occurs for fn types like `fn(&u32`). This PR restores the
original mode in those contexts.
This commit fixes another issue in the `absolute_path_not_starting_with_crate`
lint where it warns twice about an import which may contain `self`. It turns out
there were a few more locations that needed updating to use `root_id` and
`root_span` introduced in #50970 and after that it looks to work like a charm!
Closes#50978
