From c66588447440b4c1d32c75dd307dc752c83550e4 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Fri, 6 Nov 2020 03:06:08 +0100
Subject: Wrap non-block expressions in closures with a block

---
 .../src/handlers/infer_function_return_type.rs     | 43 ++++++++++++++++------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/crates/assists/src/handlers/infer_function_return_type.rs b/crates/assists/src/handlers/infer_function_return_type.rs
index 81217378a..b4944a6b0 100644
--- a/crates/assists/src/handlers/infer_function_return_type.rs
+++ b/crates/assists/src/handlers/infer_function_return_type.rs
@@ -18,38 +18,43 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // ```
 pub(crate) fn infer_function_return_type(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let expr = ctx.find_node_at_offset::<ast::Expr>()?;
-    let (tail_expr, insert_pos) = extract_tail(expr)?;
+    let (tail_expr, insert_pos, wrap_expr) = extract_tail(expr)?;
     let module = ctx.sema.scope(tail_expr.syntax()).module()?;
     let ty = ctx.sema.type_of_expr(&tail_expr).filter(|ty| !ty.is_unit())?;
     let ty = ty.display_source_code(ctx.db(), module.into()).ok()?;
 
     acc.add(
-        AssistId("change_return_type_to_result", AssistKind::RefactorRewrite),
-        "Wrap return type in Result",
+        AssistId("infer_function_return_type", AssistKind::RefactorRewrite),
+        "Add this function's return type",
         tail_expr.syntax().text_range(),
         |builder| {
             let insert_pos = insert_pos.text_range().end() + TextSize::from(1);
             builder.insert(insert_pos, &format!("-> {} ", ty));
+            if wrap_expr {
+                mark::hit!(wrap_closure_non_block_expr);
+                // `|x| x` becomes `|x| -> T x` which is invalid, so wrap it in a block
+                builder.replace(tail_expr.syntax().text_range(), &format!("{{{}}}", tail_expr));
+            }
         },
     )
 }
 
-fn extract_tail(expr: ast::Expr) -> Option<(ast::Expr, SyntaxToken)> {
-    let (ret_ty, tail_expr, insert_pos) =
+fn extract_tail(expr: ast::Expr) -> Option<(ast::Expr, SyntaxToken, bool)> {
+    let (ret_ty, tail_expr, insert_pos, wrap_expr) =
         if let Some(closure) = expr.syntax().ancestors().find_map(ast::ClosureExpr::cast) {
-            let tail_expr = match closure.body()? {
-                ast::Expr::BlockExpr(block) => block.expr()?,
-                body => body,
+            let (tail_expr, wrap_expr) = match closure.body()? {
+                ast::Expr::BlockExpr(block) => (block.expr()?, false),
+                body => (body, true),
             };
             let ret_ty = closure.ret_type();
             let rpipe = closure.param_list()?.syntax().last_token()?;
-            (ret_ty, tail_expr, rpipe)
+            (ret_ty, tail_expr, rpipe, wrap_expr)
         } else {
             let func = expr.syntax().ancestors().find_map(ast::Fn::cast)?;
             let tail_expr = func.body()?.expr()?;
             let ret_ty = func.ret_type();
             let rparen = func.param_list()?.r_paren_token()?;
-            (ret_ty, tail_expr, rparen)
+            (ret_ty, tail_expr, rparen, false)
         };
     if ret_ty.is_some() {
         mark::hit!(existing_ret_type);
@@ -61,7 +66,7 @@ fn extract_tail(expr: ast::Expr) -> Option<(ast::Expr, SyntaxToken)> {
         mark::hit!(not_tail_expr);
         return None;
     }
-    Some((tail_expr, insert_pos))
+    Some((tail_expr, insert_pos, wrap_expr))
 }
 
 #[cfg(test)]
@@ -156,13 +161,27 @@ mod tests {
 
     #[test]
     fn infer_return_type_closure() {
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+                |x: i32| { x<|> };
+            }"#,
+            r#"fn foo() {
+                |x: i32| -> i32 { x };
+            }"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_closure_wrap() {
+        mark::check!(wrap_closure_non_block_expr);
         check_assist(
             infer_function_return_type,
             r#"fn foo() {
                 |x: i32| x<|>;
             }"#,
             r#"fn foo() {
-                |x: i32| -> i32 x;
+                |x: i32| -> i32 {x};
             }"#,
         );
     }
-- 
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