Merge pull request #20817 from A4-Tacks/explicit-ty-param-in-let

Fix not applicable on param in let-stmt for add_explicit_type

Author: ShoyuVanilla

crates/ide-assists/src/handlers/add_explicit_type.rs

@@ -1,3 +1,4 @@
+use either::Either;
 use hir::HirDisplay;
 use ide_db::syntax_helpers::node_ext::walk_ty;
 use syntax::ast::{self, AstNode, LetStmt, Param};
@@ -20,7 +21,8 @@ use crate::{AssistContext, AssistId, Assists};
 // }
 // ```
 pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
-    let (ascribed_ty, expr, pat) = if let Some(let_stmt) = ctx.find_node_at_offset::<LetStmt>() {
+    let syntax_node = ctx.find_node_at_offset::<Either<LetStmt, Param>>()?;
+    let (ascribed_ty, expr, pat) = if let Either::Left(let_stmt) = syntax_node {
         let cursor_in_range = {
             let eq_range = let_stmt.eq_token()?.text_range();
             ctx.offset() < eq_range.start()
@@ -31,7 +33,7 @@ pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext<'_>) -> O
         }
 
         (let_stmt.ty(), let_stmt.initializer(), let_stmt.pat()?)
-    } else if let Some(param) = ctx.find_node_at_offset::<Param>() {
+    } else if let Either::Right(param) = syntax_node {
         if param.syntax().ancestors().nth(2).and_then(ast::ClosureExpr::cast).is_none() {
             cov_mark::hit!(add_explicit_type_not_applicable_in_fn_param);
             return None;
@@ -298,6 +300,20 @@ fn f() {
         let x: i32 = y;
     };
 }
+"#,
+        );
+
+        check_assist(
+            add_explicit_type,
+            r#"
+fn f() {
+    let f: fn(i32) = |y$0| {};
+}
+"#,
+            r#"
+fn f() {
+    let f: fn(i32) = |y: i32| {};
+}
 "#,
         );
     }