--- /dev/null
+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_lint!{
+ pub QUESTION_MARK,
+ Warn,
+ "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,
+ &format!("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);
+
+ return 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<P<Expr>> {
+ // 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());
+ }
+
+ return 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);
+ }
+}
--- /dev/null
+fn some_func(a: Option<u32>) -> Option<u32> {
+ if a.is_none() {
+ return None
+ }
+
+ a
+}
+
+pub enum SeemsOption<T> {
+ Some(T),
+ None
+}
+
+impl<T> SeemsOption<T> {
+ pub fn is_none(&self) -> bool {
+ match *self {
+ SeemsOption::None => true,
+ SeemsOption::Some(_) => false,
+ }
+ }
+}
+
+fn returns_something_similar_to_option(a: SeemsOption<u32>) -> SeemsOption<u32> {
+ if a.is_none() {
+ return SeemsOption::None;
+ }
+
+ a
+}
+
+pub struct SomeStruct {
+ pub opt: Option<u32>,
+}
+
+impl SomeStruct {
+ pub fn func(&self) -> Option<u32> {
+ if (self.opt).is_none() {
+ return None;
+ }
+
+ self.opt
+ }
+}
+
+fn main() {
+ some_func(Some(42));
+ some_func(None);
+
+ let some_struct = SomeStruct { opt: Some(54) };
+ some_struct.func();
+
+ let so = SeemsOption::Some(45);
+ returns_something_similar_to_option(so);
+}