Convert Into to From assist

This adds a "Convert Into to From" assist, useful since clippy has
recently started adding lints on every `Into`.

It covers converting the signature, and converting any `self`/`Self`
references within the body to the correct types.

It does assume that every instance of `Into` can be converted to a
`From`, which I _think_ is the case now.  Let me know if there's
something I'm not thinking of and I can try and make it smarter.

2 files changed, 9 insertions, 1 deletions

diff --git a/crates/ide_db/src/helpers.rs b/crates/ide_db/src/helpers.rs
index 9992a92bd..66798ea3a 100644
--- a/crates/ide_db/src/helpers.rs
+++ b/crates/ide_db/src/helpers.rs
@@ -93,6 +93,10 @@ impl FamousDefs<'_, '_> {
         self.find_trait("core:convert:From")
     }
 
+    pub fn core_convert_Into(&self) -> Option<Trait> {
+        self.find_trait("core:convert:Into")
+    }
+
     pub fn core_option_Option(&self) -> Option<Enum> {
         self.find_enum("core:option:Option")
     }
diff --git a/crates/ide_db/src/helpers/famous_defs_fixture.rs b/crates/ide_db/src/helpers/famous_defs_fixture.rs
index d3464ae17..4d79e064e 100644
--- a/crates/ide_db/src/helpers/famous_defs_fixture.rs
+++ b/crates/ide_db/src/helpers/famous_defs_fixture.rs
@@ -14,6 +14,10 @@ pub mod convert {
     pub trait From<T> {
         fn from(t: T) -> Self;
     }
+
+    pub trait Into<T> {
+        pub fn into(self) -> T;
+    }
 }
 
 pub mod default {
@@ -120,7 +124,7 @@ pub mod option {
 pub mod prelude {
     pub use crate::{
         cmp::Ord,
-        convert::From,
+        convert::{From, Into},
         default::Default,
         iter::{IntoIterator, Iterator},
         ops::{Fn, FnMut, FnOnce},