Merge #4570

4570: Use Chalk's built-in impls r=matklad a=flodiebold

This contains two changes:
 - Chalk has begun adding built-in representations of primitive types; use these in our type conversion logic. There's one somewhat 'iffy' part here, namely references; we don't keep track of lifetimes, but Chalk does, so it will expect a lifetime parameter on references. If we didn't provide that, it could cause crashes in Chalk code that expects the lifetime, so I rather hackily add an (always the same) lifetime placeholder during conversion. I expect that we'll fully switch to using Chalk's types everywhere before we add lifetime support, so I think this is the best solution for now.
 - let Chalk know about well-known traits (from lang items), so it can apply its built-in impls.

Before:
```
Total expressions: 181485
Expressions of unknown type: 2940 (1%)
Expressions of partially unknown type: 2884 (1%)
Type mismatches: 901
Inference: 37.821210245s, 0b allocated 0b resident
Total: 53.399467609s, 0b allocated 0b resident
```

After:
```
Total expressions: 181485
Expressions of unknown type: 2923 (1%)
Expressions of partially unknown type: 2879 (1%)
Type mismatches: 734
Inference: 39.157752509s, 0b allocated 0b resident
Total: 54.110767621s, 0b allocated 0b resident
```

(I will start splitting up `chalk.rs` in a separate PR, since it's getting pretty big...)

Co-authored-by: Florian Diebold <[email protected]>
Co-authored-by: Florian Diebold <[email protected]>

1 files changed, 8 insertions, 4 deletions

diff --git a/crates/ra_hir_def/src/lang_item.rs b/crates/ra_hir_def/src/lang_item.rs
index d96ac8c0a..d962db3cc 100644
--- a/crates/ra_hir_def/src/lang_item.rs
+++ b/crates/ra_hir_def/src/lang_item.rs
@@ -73,8 +73,8 @@ pub struct LangItems {
 }
 
 impl LangItems {
-    pub fn target<'a>(&'a self, item: &str) -> Option<&'a LangItemTarget> {
-        self.items.get(item)
+    pub fn target(&self, item: &str) -> Option<LangItemTarget> {
+        self.items.get(item).copied()
     }
 
     /// Salsa query. This will look for lang items in a specific crate.
@@ -163,9 +163,13 @@ impl LangItems {
     ) where
         T: Into<AttrDefId> + Copy,
     {
-        let attrs = db.attrs(item.into());
-        if let Some(lang_item_name) = attrs.by_key("lang").string_value() {
+        if let Some(lang_item_name) = lang_attr(db, item) {
             self.items.entry(lang_item_name.clone()).or_insert_with(|| constructor(item));
         }
     }
 }
+
+pub fn lang_attr(db: &dyn DefDatabase, item: impl Into<AttrDefId> + Copy) -> Option<SmolStr> {
+    let attrs = db.attrs(item.into());
+    attrs.by_key("lang").string_value().cloned()
+}