Correctly handle inlining of async fn

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

@@ -15,7 +15,7 @@
 };
 use itertools::{izip, Itertools};
 use syntax::{
-    ast::{self, edit_in_place::Indent, HasArgList, PathExpr},
+    ast::{self, edit::IndentLevel, edit_in_place::Indent, HasArgList, PathExpr},
     ted, AstNode, NodeOrToken, SyntaxKind,
 };
 
@@ -306,7 +306,7 @@ fn inline(
     params: &[(ast::Pat, Option<ast::Type>, hir::Param)],
     CallInfo { node, arguments, generic_arg_list }: &CallInfo,
 ) -> ast::Expr {
-    let body = if sema.hir_file_for(fn_body.syntax()).is_macro() {
+    let mut body = if sema.hir_file_for(fn_body.syntax()).is_macro() {
         cov_mark::hit!(inline_call_defined_in_macro);
         if let Some(body) = ast::BlockExpr::cast(insert_ws_into(fn_body.syntax().clone())) {
             body
@@ -391,19 +391,19 @@ fn inline(
         }
     }
 
+    let mut let_stmts = Vec::new();
+
     // Inline parameter expressions or generate `let` statements depending on whether inlining works or not.
-    for ((pat, param_ty, _), usages, expr) in izip!(params, param_use_nodes, arguments).rev() {
+    for ((pat, param_ty, _), usages, expr) in izip!(params, param_use_nodes, arguments) {
         // izip confuses RA due to our lack of hygiene info currently losing us type info causing incorrect errors
         let usages: &[ast::PathExpr] = &usages;
         let expr: &ast::Expr = expr;
 
-        let insert_let_stmt = || {
+        let mut insert_let_stmt = || {
             let ty = sema.type_of_expr(expr).filter(TypeInfo::has_adjustment).and(param_ty.clone());
-            if let Some(stmt_list) = body.stmt_list() {
-                stmt_list.push_front(
+            let_stmts.push(
                 make::let_stmt(pat.clone(), ty, Some(expr.clone())).clone_for_update().into(),
-                )
-            }
+            );
         };
 
         // check if there is a local var in the function that conflicts with parameter
@@ -457,6 +457,24 @@ fn inline(
         }
     }
 
+    let is_async_fn = function.is_async(sema.db);
+    if is_async_fn {
+        cov_mark::hit!(inline_call_async_fn);
+        body = make::async_move_block_expr(body.statements(), body.tail_expr()).clone_for_update();
+
+        // Arguments should be evaluated outside the async block, and then moved into it.
+        if !let_stmts.is_empty() {
+            cov_mark::hit!(inline_call_async_fn_with_let_stmts);
+            body.indent(IndentLevel(1));
+            body = make::block_expr(let_stmts, Some(body.into())).clone_for_update();
+        }
+    } else if let Some(stmt_list) = body.stmt_list() {
+        ted::insert_all(
+            ted::Position::after(stmt_list.l_curly_token().unwrap()),
+            let_stmts.into_iter().map(|stmt| stmt.syntax().clone().into()).collect(),
+        );
+    }
+
     let original_indentation = match node {
         ast::CallableExpr::Call(it) => it.indent_level(),
         ast::CallableExpr::MethodCall(it) => it.indent_level(),
@@ -464,7 +482,7 @@ fn inline(
     body.reindent_to(original_indentation);
 
     match body.tail_expr() {
-        Some(expr) if body.statements().next().is_none() => expr,
+        Some(expr) if !is_async_fn && body.statements().next().is_none() => expr,
         _ => match node
             .syntax()
             .parent()
@@ -1351,6 +1369,109 @@ fn main() {
         bar * b * a * 6
     };
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn async_fn_single_expression() {
+        cov_mark::check!(inline_call_async_fn);
+        check_assist(
+            inline_call,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(arg: u32) -> u32 {
+    bar(arg).await * 2
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    spawn(foo$0(42));
+}
+"#,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(arg: u32) -> u32 {
+    bar(arg).await * 2
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    spawn(async move {
+        bar(42).await * 2
+    });
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn async_fn_multiple_statements() {
+        cov_mark::check!(inline_call_async_fn);
+        check_assist(
+            inline_call,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(arg: u32) -> u32 {
+    bar(arg).await;
+    42
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    spawn(foo$0(42));
+}
+"#,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(arg: u32) -> u32 {
+    bar(arg).await;
+    42
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    spawn(async move {
+        bar(42).await;
+        42
+    });
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn async_fn_with_let_statements() {
+        cov_mark::check!(inline_call_async_fn);
+        cov_mark::check!(inline_call_async_fn_with_let_stmts);
+        check_assist(
+            inline_call,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(x: u32, y: u32, z: &u32) -> u32 {
+    bar(x).await;
+    y + y + *z
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    let var = 42;
+    spawn(foo$0(var, var + 1, &var));
+}
+"#,
+            r#"
+async fn bar(x: u32) -> u32 { x + 1 }
+async fn foo(x: u32, y: u32, z: &u32) -> u32 {
+    bar(x).await;
+    y + y + *z
+}
+fn spawn<T>(_: T) {}
+fn main() {
+    let var = 42;
+    spawn({
+        let y = var + 1;
+        let z: &u32 = &var;
+        async move {
+            bar(var).await;
+            y + y + *z
+        }
+    });
+}
 "#,
         );
     }

crates/syntax/src/ast/make.rs

@@ -447,6 +447,21 @@ pub fn block_expr(
     ast_from_text(&format!("fn f() {buf}"))
 }
 
+pub fn async_move_block_expr(
+    stmts: impl IntoIterator<Item = ast::Stmt>,
+    tail_expr: Option<ast::Expr>,
+) -> ast::BlockExpr {
+    let mut buf = "async move {\n".to_string();
+    for stmt in stmts.into_iter() {
+        format_to!(buf, "    {stmt}\n");
+    }
+    if let Some(tail_expr) = tail_expr {
+        format_to!(buf, "    {tail_expr}\n");
+    }
+    buf += "}";
+    ast_from_text(&format!("const _: () = {buf};"))
+}
+
 pub fn tail_only_block_expr(tail_expr: ast::Expr) -> ast::BlockExpr {
     ast_from_text(&format!("fn f() {{ {tail_expr} }}"))
 }