Add question mark operator

clippy_lints/src/lib.rs

@@ -89,6 +89,7 @@ macro_rules! declare_restriction_lint {
 pub mod double_comparison;
 pub mod double_parens;
 pub mod drop_forget_ref;
+pub mod question_mark;
 pub mod else_if_without_else;
 pub mod empty_enum;
 pub mod entry;
@@ -371,6 +372,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_late_lint_pass(box replace_consts::ReplaceConsts);
     reg.register_late_lint_pass(box types::UnitArg);
     reg.register_late_lint_pass(box double_comparison::DoubleComparisonPass);
+    reg.register_late_lint_pass(box question_mark::QuestionMarkPass);
 
     reg.register_lint_group("clippy_restrictions", vec![
         arithmetic::FLOAT_ARITHMETIC,

clippy_lints/src/question_mark.rs

@@ -0,0 +1,138 @@
+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);
+    }
+}

tests/ui/question_mark.rs

@@ -0,0 +1,54 @@
+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);
+}