2 files changed, 350 insertions, 30 deletions

diff --git a/crates/assists/src/handlers/extract_function.rs b/crates/assists/src/handlers/extract_function.rs
index 4372479b9..225a50d2d 100644
--- a/crates/assists/src/handlers/extract_function.rs
+++ b/crates/assists/src/handlers/extract_function.rs
@@ -84,7 +84,7 @@ pub(crate) fn extract_function(acc: &mut Assists, ctx: &AssistContext) -> Option
         // We should not have variables that outlive body if we have expression block
         return None;
     }
-    let control_flow = external_control_flow(&body)?;
+    let control_flow = external_control_flow(ctx, &body)?;
 
     let target_range = body.text_range();
 
@@ -117,7 +117,7 @@ pub(crate) fn extract_function(acc: &mut Assists, ctx: &AssistContext) -> Option
     )
 }
 
-fn external_control_flow(body: &FunctionBody) -> Option<ControlFlow> {
+fn external_control_flow(ctx: &AssistContext, body: &FunctionBody) -> Option<ControlFlow> {
     let mut ret_expr = None;
     let mut try_expr = None;
     let mut break_expr = None;
@@ -180,35 +180,71 @@ fn external_control_flow(body: &FunctionBody) -> Option<ControlFlow> {
         }
     }
 
-    if try_expr.is_some() {
-        // FIXME: support try
-        return None;
-    }
+    let kind = match (try_expr, ret_expr, break_expr, continue_expr) {
+        (Some(e), None, None, None) => {
+            let func = e.syntax().ancestors().find_map(ast::Fn::cast)?;
+            let def = ctx.sema.to_def(&func)?;
+            let ret_ty = def.ret_type(ctx.db());
+            let kind = try_kind_of_ty(ret_ty, ctx)?;
 
-    let kind = match (ret_expr, break_expr, continue_expr) {
-        (Some(r), None, None) => match r.expr() {
+            Some(FlowKind::Try { kind })
+        }
+        (Some(_), Some(r), None, None) => match r.expr() {
+            Some(expr) => {
+                if let Some(kind) = expr_err_kind(&expr, ctx) {
+                    Some(FlowKind::TryReturn { expr, kind })
+                } else {
+                    mark::hit!(external_control_flow_try_and_return_non_err);
+                    return None;
+                }
+            }
+            None => return None,
+        },
+        (Some(_), _, _, _) => {
+            mark::hit!(external_control_flow_try_and_bc);
+            return None;
+        }
+        (None, Some(r), None, None) => match r.expr() {
             Some(expr) => Some(FlowKind::ReturnValue(expr)),
             None => Some(FlowKind::Return),
         },
-        (Some(_), _, _) => {
+        (None, Some(_), _, _) => {
             mark::hit!(external_control_flow_return_and_bc);
             return None;
         }
-        (None, Some(_), Some(_)) => {
+        (None, None, Some(_), Some(_)) => {
             mark::hit!(external_control_flow_break_and_continue);
             return None;
         }
-        (None, Some(b), None) => match b.expr() {
+        (None, None, Some(b), None) => match b.expr() {
             Some(expr) => Some(FlowKind::BreakValue(expr)),
             None => Some(FlowKind::Break),
         },
-        (None, None, Some(_)) => Some(FlowKind::Continue),
-        (None, None, None) => None,
+        (None, None, None, Some(_)) => Some(FlowKind::Continue),
+        (None, None, None, None) => None,
     };
 
     Some(ControlFlow { kind })
 }
 
+/// Checks is expr is `Err(_)` or `None`
+fn expr_err_kind(expr: &ast::Expr, ctx: &AssistContext) -> Option<TryKind> {
+    let call_expr = match expr {
+        ast::Expr::CallExpr(call_expr) => call_expr,
+        _ => return None,
+    };
+    let func = call_expr.expr()?;
+    let text = func.syntax().text();
+
+    if text == "Err" {
+        Some(TryKind::Result { ty: ctx.sema.type_of_expr(expr)? })
+    } else if text == "None" {
+        Some(TryKind::Option)
+    } else {
+        None
+    }
+}
+
 #[derive(Debug)]
 struct Function {
     name: String,
@@ -330,6 +366,13 @@ enum FlowKind {
     Return,
     /// Return with value (`return $expr;`)
     ReturnValue(ast::Expr),
+    Try {
+        kind: TryKind,
+    },
+    TryReturn {
+        expr: ast::Expr,
+        kind: TryKind,
+    },
     /// Break without value (`return;`)
     Break,
     /// Break with value (`break $expr;`)
@@ -338,11 +381,21 @@ enum FlowKind {
     Continue,
 }
 
+#[derive(Debug, Clone)]
+enum TryKind {
+    Option,
+    Result { ty: hir::Type },
+}
+
 impl FlowKind {
-    fn make_expr(&self, expr: Option<ast::Expr>) -> ast::Expr {
+    fn make_result_handler(&self, expr: Option<ast::Expr>) -> ast::Expr {
         match self {
             FlowKind::Return | FlowKind::ReturnValue(_) => make::expr_return(expr),
             FlowKind::Break | FlowKind::BreakValue(_) => make::expr_break(expr),
+            FlowKind::Try { .. } | FlowKind::TryReturn { .. } => {
+                stdx::never!("cannot have result handler with try");
+                expr.unwrap_or_else(|| make::expr_return(None))
+            }
             FlowKind::Continue => {
                 stdx::always!(expr.is_none(), "continue with value is not possible");
                 make::expr_continue()
@@ -352,12 +405,34 @@ impl FlowKind {
 
     fn expr_ty(&self, ctx: &AssistContext) -> Option<hir::Type> {
         match self {
-            FlowKind::ReturnValue(expr) | FlowKind::BreakValue(expr) => ctx.sema.type_of_expr(expr),
+            FlowKind::ReturnValue(expr)
+            | FlowKind::BreakValue(expr)
+            | FlowKind::TryReturn { expr, .. } => ctx.sema.type_of_expr(expr),
+            FlowKind::Try { .. } => {
+                stdx::never!("try does not have defined expr_ty");
+                None
+            }
             FlowKind::Return | FlowKind::Break | FlowKind::Continue => None,
         }
     }
 }
 
+fn try_kind_of_ty(ty: hir::Type, ctx: &AssistContext) -> Option<TryKind> {
+    if ty.is_unknown() {
+        // We favour Result for `expr?`
+        return Some(TryKind::Result { ty });
+    }
+    let adt = ty.as_adt()?;
+    let name = adt.name(ctx.db());
+    // FIXME: use lang items to determine if it is std type or user defined
+    //        E.g. if user happens to define type named `Option`, we would have false positive
+    match name.to_string().as_str() {
+        "Option" => Some(TryKind::Option),
+        "Result" => Some(TryKind::Result { ty }),
+        _ => None,
+    }
+}
+
 #[derive(Debug)]
 enum RetType {
     Expr(hir::Type),
@@ -851,7 +926,7 @@ fn format_replacement(ctx: &AssistContext, fun: &Function, indent: IndentLevel)
 
     let handler = FlowHandler::from_ret_ty(fun, &ret_ty);
 
-    let expr = handler.make_expr(call_expr).indent(indent);
+    let expr = handler.make_call_expr(call_expr).indent(indent);
 
     let mut buf = String::new();
     match fun.vars_defined_in_body_and_outlive.as_slice() {
@@ -877,6 +952,7 @@ fn format_replacement(ctx: &AssistContext, fun: &Function, indent: IndentLevel)
 
 enum FlowHandler {
     None,
+    Try { kind: TryKind },
     If { action: FlowKind },
     IfOption { action: FlowKind },
     MatchOption { none: FlowKind },
@@ -897,6 +973,9 @@ impl FlowHandler {
                         FlowKind::ReturnValue(_) | FlowKind::BreakValue(_) => {
                             FlowHandler::IfOption { action }
                         }
+                        FlowKind::Try { kind } | FlowKind::TryReturn { kind, .. } => {
+                            FlowHandler::Try { kind: kind.clone() }
+                        }
                     }
                 } else {
                     match flow_kind {
@@ -906,17 +985,21 @@ impl FlowHandler {
                         FlowKind::ReturnValue(_) | FlowKind::BreakValue(_) => {
                             FlowHandler::MatchResult { err: action }
                         }
+                        FlowKind::Try { kind } | FlowKind::TryReturn { kind, .. } => {
+                            FlowHandler::Try { kind: kind.clone() }
+                        }
                     }
                 }
             }
         }
     }
 
-    fn make_expr(&self, call_expr: ast::Expr) -> ast::Expr {
+    fn make_call_expr(&self, call_expr: ast::Expr) -> ast::Expr {
         match self {
             FlowHandler::None => call_expr,
+            FlowHandler::Try { kind: _ } => make::expr_try(call_expr),
             FlowHandler::If { action } => {
-                let action = action.make_expr(None);
+                let action = action.make_result_handler(None);
                 let stmt = make::expr_stmt(action);
                 let block = make::block_expr(iter::once(stmt.into()), None);
                 let condition = make::condition(call_expr, None);
@@ -928,7 +1011,7 @@ impl FlowHandler {
                 let pattern = make::tuple_struct_pat(path, iter::once(value_pat.into()));
                 let cond = make::condition(call_expr, Some(pattern.into()));
                 let value = make::expr_path(make_path_from_text("value"));
-                let action_expr = action.make_expr(Some(value));
+                let action_expr = action.make_result_handler(Some(value));
                 let action_stmt = make::expr_stmt(action_expr);
                 let then = make::block_expr(iter::once(action_stmt.into()), None);
                 make::expr_if(cond, then, None)
@@ -946,7 +1029,7 @@ impl FlowHandler {
                 let none_arm = {
                     let path = make_path_from_text("None");
                     let pat = make::path_pat(path);
-                    make::match_arm(iter::once(pat), none.make_expr(None))
+                    make::match_arm(iter::once(pat), none.make_result_handler(None))
                 };
                 let arms = make::match_arm_list(vec![some_arm, none_arm]);
                 make::expr_match(call_expr, arms)
@@ -967,7 +1050,7 @@ impl FlowHandler {
                     let value_pat = make::ident_pat(make::name(err_name));
                     let pat = make::tuple_struct_pat(path, iter::once(value_pat.into()));
                     let value = make::expr_path(make_path_from_text(err_name));
-                    make::match_arm(iter::once(pat.into()), err.make_expr(Some(value)))
+                    make::match_arm(iter::once(pat.into()), err.make_result_handler(Some(value)))
                 };
                 let arms = make::match_arm_list(vec![ok_arm, err_arm]);
                 make::expr_match(call_expr, arms)
@@ -1035,14 +1118,25 @@ impl FunType {
 }
 
 fn make_ret_ty(ctx: &AssistContext, module: hir::Module, fun: &Function) -> Option<ast::RetType> {
-    let ty = fun.return_type(ctx);
-    let handler = FlowHandler::from_ret_ty(fun, &ty);
+    let fun_ty = fun.return_type(ctx);
+    let handler = FlowHandler::from_ret_ty(fun, &fun_ty);
     let ret_ty = match &handler {
         FlowHandler::None => {
-            if matches!(ty, FunType::Unit) {
+            if matches!(fun_ty, FunType::Unit) {
                 return None;
             }
-            ty.make_ty(ctx, module)
+            fun_ty.make_ty(ctx, module)
+        }
+        FlowHandler::Try { kind: TryKind::Option } => {
+            make::ty_generic(make::name_ref("Option"), iter::once(fun_ty.make_ty(ctx, module)))
+        }
+        FlowHandler::Try { kind: TryKind::Result { ty: parent_ret_ty } } => {
+            let handler_ty =
+                result_err_ty(parent_ret_ty, ctx, module).unwrap_or_else(make::ty_unit);
+            make::ty_generic(
+                make::name_ref("Result"),
+                vec![fun_ty.make_ty(ctx, module), handler_ty],
+            )
         }
         FlowHandler::If { .. } => make::ty("bool"),
         FlowHandler::IfOption { action } => {
@@ -1053,17 +1147,42 @@ fn make_ret_ty(ctx: &AssistContext, module: hir::Module, fun: &Function) -> Opti
             make::ty_generic(make::name_ref("Option"), iter::once(handler_ty))
         }
         FlowHandler::MatchOption { .. } => {
-            make::ty_generic(make::name_ref("Option"), iter::once(ty.make_ty(ctx, module)))
+            make::ty_generic(make::name_ref("Option"), iter::once(fun_ty.make_ty(ctx, module)))
         }
         FlowHandler::MatchResult { err } => {
             let handler_ty =
                 err.expr_ty(ctx).map(|ty| make_ty(&ty, ctx, module)).unwrap_or_else(make::ty_unit);
-            make::ty_generic(make::name_ref("Result"), vec![ty.make_ty(ctx, module), handler_ty])
+            make::ty_generic(
+                make::name_ref("Result"),
+                vec![fun_ty.make_ty(ctx, module), handler_ty],
+            )
         }
     };
     Some(make::ret_type(ret_ty))
 }
 
+/// Extract `E` type from `Result<T, E>`
+fn result_err_ty(
+    parent_ret_ty: &hir::Type,
+    ctx: &AssistContext,
+    module: hir::Module,
+) -> Option<ast::Type> {
+    // FIXME: use hir to extract argument information
+    //        currently we use `format -> take part -> parse`
+    let path_ty = match make_ty(&parent_ret_ty, ctx, module) {
+        ast::Type::PathType(path_ty) => path_ty,
+        _ => return None,
+    };
+    let arg_list = path_ty.path()?.segment()?.generic_arg_list()?;
+    let err_arg = arg_list.generic_args().nth(1)?;
+    let type_arg = match err_arg {
+        ast::GenericArg::TypeArg(type_arg) => type_arg,
+        _ => return None,
+    };
+
+    type_arg.ty()
+}
+
 fn make_body(
     ctx: &AssistContext,
     old_indent: IndentLevel,
@@ -1128,6 +1247,18 @@ fn make_body(
 
     let block = match &handler {
         FlowHandler::None => block,
+        FlowHandler::Try { kind } => {
+            let block = with_default_tail_expr(block, make::expr_unit());
+            map_tail_expr(block, |tail_expr| {
+                let constructor = match kind {
+                    TryKind::Option => "Some",
+                    TryKind::Result { .. } => "Ok",
+                };
+                let func = make::expr_path(make_path_from_text(constructor));
+                let args = make::arg_list(iter::once(tail_expr));
+                make::expr_call(func, args)
+            })
+        }
         FlowHandler::If { .. } => {
             let lit_false = ast::Literal::cast(make::tokens::literal("false").parent()).unwrap();
             with_tail_expr(block, lit_false.into())
@@ -1142,9 +1273,9 @@ fn make_body(
             make::expr_call(some, args)
         }),
         FlowHandler::MatchResult { .. } => map_tail_expr(block, |tail_expr| {
-            let some = make::expr_path(make_path_from_text("Ok"));
+            let ok = make::expr_path(make_path_from_text("Ok"));
             let args = make::arg_list(iter::once(tail_expr));
-            make::expr_call(some, args)
+            make::expr_call(ok, args)
         }),
     };
 
@@ -1159,6 +1290,13 @@ fn map_tail_expr(block: ast::BlockExpr, f: impl FnOnce(ast::Expr) -> ast::Expr)
     make::block_expr(block.statements(), Some(f(tail_expr)))
 }
 
+fn with_default_tail_expr(block: ast::BlockExpr, tail_expr: ast::Expr) -> ast::BlockExpr {
+    match block.tail_expr() {
+        Some(_) => block,
+        None => make::block_expr(block.statements(), Some(tail_expr)),
+    }
+}
+
 fn with_tail_expr(block: ast::BlockExpr, tail_expr: ast::Expr) -> ast::BlockExpr {
     let stmt_tail = block.tail_expr().map(|expr| make::expr_stmt(expr).into());
     let stmts = block.statements().chain(stmt_tail);
@@ -1295,7 +1433,7 @@ fn update_external_control_flow(handler: &FlowHandler, syntax: &SyntaxNode) -> S
 
 fn make_rewritten_flow(handler: &FlowHandler, arg_expr: Option<ast::Expr>) -> Option<ast::Expr> {
     let value = match handler {
-        FlowHandler::None => return None,
+        FlowHandler::None | FlowHandler::Try { .. } => return None,
         FlowHandler::If { .. } => {
             ast::Literal::cast(make::tokens::literal("true").parent()).unwrap().into()
         }
@@ -3039,4 +3177,183 @@ fn $0fun_name() -> Result<i32, i64> {
 }"##,
         );
     }
+
+    #[test]
+    fn try_option() {
+        check_assist(
+            extract_function,
+            r##"
+enum Option<T> { None, Some(T), }
+use Option::*;
+fn bar() -> Option<i32> { None }
+fn foo() -> Option<()> {
+    let n = bar()?;
+    $0let k = foo()?;
+    let m = k + 1;$0
+    let h = 1 + m;
+    Some(())
+}"##,
+            r##"
+enum Option<T> { None, Some(T), }
+use Option::*;
+fn bar() -> Option<i32> { None }
+fn foo() -> Option<()> {
+    let n = bar()?;
+    let m = fun_name()?;
+    let h = 1 + m;
+    Some(())
+}
+
+fn $0fun_name() -> Option<i32> {
+    let k = foo()?;
+    let m = k + 1;
+    Some(m)
+}"##,
+        );
+    }
+
+    #[test]
+    fn try_option_unit() {
+        check_assist(
+            extract_function,
+            r##"
+enum Option<T> { None, Some(T), }
+use Option::*;
+fn foo() -> Option<()> {
+    let n = 1;
+    $0let k = foo()?;
+    let m = k + 1;$0
+    let h = 1 + n;
+    Some(())
+}"##,
+            r##"
+enum Option<T> { None, Some(T), }
+use Option::*;
+fn foo() -> Option<()> {
+    let n = 1;
+    fun_name()?;
+    let h = 1 + n;
+    Some(())
+}
+
+fn $0fun_name() -> Option<()> {
+    let k = foo()?;
+    let m = k + 1;
+    Some(())
+}"##,
+        );
+    }
+
+    #[test]
+    fn try_result() {
+        check_assist(
+            extract_function,
+            r##"
+enum Result<T, E> { Ok(T), Err(E), }
+use Result::*;
+fn foo() -> Result<(), i64> {
+    let n = 1;
+    $0let k = foo()?;
+    let m = k + 1;$0
+    let h = 1 + m;
+    Ok(())
+}"##,
+            r##"
+enum Result<T, E> { Ok(T), Err(E), }
+use Result::*;
+fn foo() -> Result<(), i64> {
+    let n = 1;
+    let m = fun_name()?;
+    let h = 1 + m;
+    Ok(())
+}
+
+fn $0fun_name() -> Result<i32, i64> {
+    let k = foo()?;
+    let m = k + 1;
+    Ok(m)
+}"##,
+        );
+    }
+
+    #[test]
+    fn try_result_with_return() {
+        check_assist(
+            extract_function,
+            r##"
+enum Result<T, E> { Ok(T), Err(E), }
+use Result::*;
+fn foo() -> Result<(), i64> {
+    let n = 1;
+    $0let k = foo()?;
+    if k == 42 {
+        return Err(1);
+    }
+    let m = k + 1;$0
+    let h = 1 + m;
+    Ok(())
+}"##,
+            r##"
+enum Result<T, E> { Ok(T), Err(E), }
+use Result::*;
+fn foo() -> Result<(), i64> {
+    let n = 1;
+    let m = fun_name()?;
+    let h = 1 + m;
+    Ok(())
+}
+
+fn $0fun_name() -> Result<i32, i64> {
+    let k = foo()?;
+    if k == 42 {
+        return Err(1);
+    }
+    let m = k + 1;
+    Ok(m)
+}"##,
+        );
+    }
+
+    #[test]
+    fn try_and_break() {
+        mark::check!(external_control_flow_try_and_bc);
+        check_assist_not_applicable(
+            extract_function,
+            r##"
+enum Option<T> { None, Some(T) }
+use Option::*;
+fn foo() -> Option<()> {
+    loop {
+        let n = Some(1);
+        $0let m = n? + 1;
+        break;
+        let k = 2;
+        let k = k + 1;$0
+        let r = n + k;
+    }
+    Some(())
+}"##,
+        );
+    }
+
+    #[test]
+    fn try_and_return_ok() {
+        mark::check!(external_control_flow_try_and_return_non_err);
+        check_assist_not_applicable(
+            extract_function,
+            r##"
+enum Result<T, E> { Ok(T), Err(E), }
+use Result::*;
+fn foo() -> Result<(), i64> {
+    let n = 1;
+    $0let k = foo()?;
+    if k == 42 {
+        return Ok(1);
+    }
+    let m = k + 1;$0
+    let h = 1 + m;
+    Ok(())
+}"##,
+        );
+    }
 }
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 5f6b96c23..5eee33545 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -200,6 +200,9 @@ pub fn expr_return(expr: Option<ast::Expr>) -> ast::Expr {
         None => expr_from_text("return"),
     }
 }
+pub fn expr_try(expr: ast::Expr) -> ast::Expr {
+    expr_from_text(&format!("{}?", expr))
+}
 pub fn expr_match(expr: ast::Expr, match_arm_list: ast::MatchArmList) -> ast::Expr {
     expr_from_text(&format!("match {} {}", expr, match_arm_list))
 }