Merge #3814

3814: Add impl From for enum variant assist r=flodiebold a=mattyhall

Basically adds a From impl for tuple enum variants with one field. It was recommended to me on the zulip to maybe try using the trait solver, but I had trouble with that as, although it could resolve the trait impl, it couldn't resolve the variable unambiguously in real use. I'm also unsure of how it would work if there were already multiple From impls to resolve - I can't see a way we could get more than one solution to my query.

Fixes #3766

Co-authored-by: Matthew Hall <[email protected]>

1 files changed, 20 insertions, 0 deletions

diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index cd2a8fc62..c6f3bdb8e 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -1084,6 +1084,26 @@ impl Type {
         )
     }
 
+    pub fn impls_trait(&self, db: &dyn HirDatabase, trait_: Trait, args: &[Type]) -> bool {
+        let trait_ref = hir_ty::TraitRef {
+            trait_: trait_.id,
+            substs: Substs::build_for_def(db, trait_.id)
+                .push(self.ty.value.clone())
+                .fill(args.iter().map(|t| t.ty.value.clone()))
+                .build(),
+        };
+
+        let goal = Canonical {
+            value: hir_ty::InEnvironment::new(
+                self.ty.environment.clone(),
+                hir_ty::Obligation::Trait(trait_ref),
+            ),
+            num_vars: 0,
+        };
+
+        db.trait_solve(self.krate, goal).is_some()
+    }
+
     // FIXME: this method is broken, as it doesn't take closures into account.
     pub fn as_callable(&self) -> Option<CallableDef> {
         Some(self.ty.value.as_callable()?.0)