use rustc::lint::*; use rustc::hir::*; use rustc::hir::def::Def; use utils::sugg::Sugg; use syntax::ptr::P; use utils::{match_def_path, match_type, span_lint_and_then}; use utils::paths::*; /// **What it does:** Checks for expressions that could be replaced by the question mark operator /// /// **Why is this bad?** Question mark usage is more idiomatic /// /// **Known problems:** None /// /// **Example:** /// ```rust /// if option.is_none() { /// return None; /// } /// ``` /// /// Could be written: /// /// ```rust /// option?; /// ``` declare_clippy_lint!{ pub QUESTION_MARK, style, "checks for expressions that could be replaced by the question mark operator" } #[derive(Copy, Clone)] pub struct QuestionMarkPass; impl LintPass for QuestionMarkPass { fn get_lints(&self) -> LintArray { lint_array!(QUESTION_MARK) } } impl QuestionMarkPass { /// Check if the given expression on the given context matches the following structure: /// /// ``` /// if option.is_none() { /// return None; /// } /// ``` /// /// If it matches, it will suggest to use the question mark operator instead fn check_is_none_and_early_return_none(cx: &LateContext, expr: &Expr) { if_chain! { if let ExprIf(ref if_expr, ref body, _) = expr.node; if let ExprMethodCall(ref segment, _, ref args) = if_expr.node; if segment.name == "is_none"; if Self::expression_returns_none(cx, body); if let Some(subject) = args.get(0); if Self::is_option(cx, subject); then { span_lint_and_then( cx, QUESTION_MARK, expr.span, "this block may be rewritten with the `?` operator", |db| { let receiver_str = &Sugg::hir(cx, subject, ".."); db.span_suggestion( expr.span, "replace_it_with", format!("{}?;", receiver_str), ); } ) } } } fn is_option(cx: &LateContext, expression: &Expr) -> bool { let expr_ty = cx.tables.expr_ty(expression); match_type(cx, expr_ty, &OPTION) } fn expression_returns_none(cx: &LateContext, expression: &Expr) -> bool { match expression.node { ExprBlock(ref block, _) => { if let Some(return_expression) = Self::return_expression(block) { return Self::expression_returns_none(cx, &return_expression); } false }, ExprRet(Some(ref expr)) => { Self::expression_returns_none(cx, expr) }, ExprPath(ref qp) => { if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) { return match_def_path(cx.tcx, def_id, &OPTION_NONE); } false }, _ => false } } fn return_expression(block: &Block) -> Option
> { // Check if last expression is a return statement. Then, return the expression if_chain! { if block.stmts.len() == 1; if let Some(expr) = block.stmts.iter().last(); if let StmtSemi(ref expr, _) = expr.node; if let ExprRet(ref ret_expr) = expr.node; if let &Some(ref ret_expr) = ret_expr; then { return Some(ret_expr.clone()); } } // Check if the block has an implicit return expression if let Some(ref ret_expr) = block.expr { return Some(ret_expr.clone()); } None } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMarkPass { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { Self::check_is_none_and_early_return_none(cx, expr); } }