- The FCP for such issues lasts for one cycle. In the final week or two of the
  cycle, we will review comments and make a final determination:

  - Convert to error: the change should be made into a hard error.
  - Revert: we should remove the warning and continue to allow the older code to
    compile.
  - Defer: can't decide yet, wait longer, or try other strategies.

Ideally, breaking changes should have landed on the **stable branch** of the
compiler before they are finalized.

<a id="guide"></a>

### Removing a lint

Once we have decided to make a "future warning" into a hard error, we need a PR
that removes the custom lint. As an example, here are the steps required to
remove the `overlapping_inherent_impls` compatibility lint. First, convert the
name of the lint to uppercase (`OVERLAPPING_INHERENT_IMPLS`) ripgrep through the
source for that string. We will basically by converting each place where this
lint name is mentioned (in the compiler, we use the upper-case name, and a macro
automatically generates the lower-case string; so searching for
`overlapping_inherent_impls` would not find much).

> NOTE: these exact files don't exist anymore, but the procedure is still the same.

#### Remove the lint.

The first reference you will likely find is the lint definition [in
`rustc_session/src/lint/builtin.rs` that resembles this][defsource]:


```rust
declare_lint! {
    pub OVERLAPPING_INHERENT_IMPLS,
    Deny, // this may also say Warning
    "two overlapping inherent impls define an item with the same name were erroneously allowed"
}
```

This `declare_lint!` macro creates the relevant data structures. Remove it. You
will also find that there is a mention of `OVERLAPPING_INHERENT_IMPLS` later in
the file as [part of a `lint_array!`][lintarraysource]; remove it too.


Next, you see [a reference to `OVERLAPPING_INHERENT_IMPLS` in
`rustc_lint/src/lib.rs`][futuresource]. This is defining the lint as a "future
compatibility lint":

```rust
FutureIncompatibleInfo {
    id: LintId::of(OVERLAPPING_INHERENT_IMPLS),
    reference: "issue #36889 <https://github.com/rust-lang/rust/issues/36889>",