add_explicit_type respects coercions

crates/hir/src/semantics.rs

@@ -216,6 +216,10 @@ pub fn type_of_expr(&self, expr: &ast::Expr) -> Option<Type> {
         self.imp.type_of_expr(expr)
     }
 
+    pub fn type_of_expr_with_coercion(&self, expr: &ast::Expr) -> Option<Type> {
+        self.imp.type_of_expr_with_coercion(expr)
+    }
+
     pub fn type_of_pat(&self, pat: &ast::Pat) -> Option<Type> {
         self.imp.type_of_pat(pat)
     }
@@ -560,6 +564,10 @@ fn type_of_expr(&self, expr: &ast::Expr) -> Option<Type> {
         self.analyze(expr.syntax()).type_of_expr(self.db, expr)
     }
 
+    fn type_of_expr_with_coercion(&self, expr: &ast::Expr) -> Option<Type> {
+        self.analyze(expr.syntax()).type_of_expr_with_coercion(self.db, expr)
+    }
+
     fn type_of_pat(&self, pat: &ast::Pat) -> Option<Type> {
         self.analyze(pat.syntax()).type_of_pat(self.db, pat)
     }

crates/hir/src/source_analyzer.rs

@@ -122,6 +122,21 @@ pub(crate) fn type_of_expr(&self, db: &dyn HirDatabase, expr: &ast::Expr) -> Opt
         Type::new_with_resolver(db, &self.resolver, ty)
     }
 
+    pub(crate) fn type_of_expr_with_coercion(
+        &self,
+        db: &dyn HirDatabase,
+        expr: &ast::Expr,
+    ) -> Option<Type> {
+        let expr_id = self.expr_id(db, expr)?;
+        let infer = self.infer.as_ref()?;
+        let ty = infer
+            .expr_adjustments
+            .get(&expr_id)
+            .and_then(|adjusts| adjusts.last().map(|adjust| &adjust.target))
+            .unwrap_or_else(|| &infer[expr_id]);
+        Type::new_with_resolver(db, &self.resolver, ty.clone())
+    }
+
     pub(crate) fn type_of_pat(&self, db: &dyn HirDatabase, pat: &ast::Pat) -> Option<Type> {
         let pat_id = self.pat_id(pat)?;
         let ty = self.infer.as_ref()?[pat_id].clone();

crates/hir_ty/src/tests/coercion.rs

@@ -46,7 +46,7 @@ fn test2() {
 
 #[test]
 fn let_stmt_coerce() {
-    check_no_mismatches(
+    check(
         r"
 //- minicore: coerce_unsized
 fn test() {

crates/ide_assists/src/handlers/add_explicit_type.rs

@@ -55,7 +55,7 @@ pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext) -> Optio
     }
 
     // Infer type
-    let ty = ctx.sema.type_of_expr(&expr)?;
+    let ty = ctx.sema.type_of_expr_with_coercion(&expr)?;
     if ty.contains_unknown() || ty.is_closure() {
         cov_mark::hit!(add_explicit_type_not_applicable_if_ty_not_inferred);
         return None;
@@ -258,6 +258,24 @@ fn main() {
 fn main() {
     let test @ (): () = ();
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_inserts_coercions() {
+        check_assist(
+            add_explicit_type,
+            r#"
+//- minicore: coerce_unsized
+fn f() {
+    let $0x: *const [_] = &[3];
+}
+"#,
+            r#"
+fn f() {
+    let x: *const [i32] = &[3];
+}
 "#,
         );
     }