question_mark: Add check for else branch

cc #2841

Author: sinkuu

clippy_lints/src/question_mark.rs

@@ -17,7 +17,7 @@ use if_chain::if_chain;
 
 use crate::rustc_errors::Applicability;
 use crate::utils::paths::*;
-use crate::utils::{match_def_path, match_type, span_lint_and_then};
+use crate::utils::{match_def_path, match_type, span_lint_and_then, SpanlessEq};
 
 /// **What it does:** Checks for expressions that could be replaced by the question mark operator
 ///
@@ -64,14 +64,27 @@ impl Pass {
     /// 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 ExprKind::If(ref if_expr, ref body, _) = expr.node;
-            if let ExprKind::MethodCall(ref segment, _, ref args) = if_expr.node;
+            if let ExprKind::If(if_expr, body, else_) = &expr.node;
+            if let ExprKind::MethodCall(segment, _, args) = &if_expr.node;
             if segment.ident.name == "is_none";
             if Self::expression_returns_none(cx, body);
             if let Some(subject) = args.get(0);
             if Self::is_option(cx, subject);
 
             then {
+                if let Some(else_) = else_ {
+                    if_chain! {
+                        if let ExprKind::Block(block, None) = &else_.node;
+                        if block.stmts.len() == 0;
+                        if let Some(expr) = &block.expr;
+                        if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, expr);
+                        then {
+                        } else {
+                            return
+                        }
+                    }
+                }
+
                 span_lint_and_then(
                     cx,
                     QUESTION_MARK,

tests/ui/question_mark.rs

@@ -49,6 +49,22 @@ impl SomeStruct {
 
         self.opt
     }
+
+    pub fn func2(&self) -> Option<u32> {
+        let _ = if self.opt.is_none() {
+            return None;
+        } else {
+            self.opt
+        };
+
+        let _ = if self.opt.is_none() {
+            return None;
+        } else {
+            0
+        };
+
+        self.opt
+    }
 }
 
 fn main() {

tests/ui/question_mark.stderr

@@ -16,5 +16,16 @@ error: this block may be rewritten with the `?` operator
 48 | |         }
    | |_________^ help: replace_it_with: `(self.opt)?;`
 
-error: aborting due to 2 previous errors
+error: this block may be rewritten with the `?` operator
+  --> $DIR/question_mark.rs:54:17
+   |
+54 |           let _ = if self.opt.is_none() {
+   |  _________________^
+55 | |             return None;
+56 | |         } else {
+57 | |             self.opt
+58 | |         };
+   | |_________^ help: replace_it_with: `self.opt?;`
+
+error: aborting due to 3 previous errors