Merge pull request #1347 from sinkuu/conditional_returns

Allow explicit returns with cfg attributes

Author: oli-obk

clippy_lints/src/returns.rs

@@ -61,7 +61,10 @@ impl ReturnPass {
         match expr.node {
             // simple return is always "bad"
             ast::ExprKind::Ret(Some(ref inner)) => {
-                self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
+                // allow `#[cfg(a)] return a; #[cfg(b)] return b;`
+                if !expr.attrs.iter().any(attr_is_cfg) {
+                    self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
+                }
             }
             // a whole block? check it!
             ast::ExprKind::Block(ref block) => {
@@ -105,6 +108,7 @@ impl ReturnPass {
             let ast::StmtKind::Expr(ref retexpr) = retexpr.node,
             let Some(stmt) = it.next_back(),
             let ast::StmtKind::Local(ref local) = stmt.node,
+            !local.attrs.iter().any(attr_is_cfg),
             let Some(ref initexpr) = local.init,
             let ast::PatKind::Ident(_, Spanned { node: id, .. }, _) = local.pat.node,
             let ast::ExprKind::Path(_, ref path) = retexpr.node,
@@ -140,3 +144,12 @@ impl EarlyLintPass for ReturnPass {
         self.check_let_return(cx, block);
     }
 }
+
+fn attr_is_cfg(attr: &ast::Attribute) -> bool {
+    if let ast::MetaItemKind::List(ref key, _) = attr.node.value.node {
+        *key == "cfg"
+    } else {
+        false
+    }
+}
+

tests/run-pass/returns.rs

@@ -0,0 +1,19 @@
+#[deny(warnings)]
+fn cfg_return() -> i32 {
+    #[cfg(unix)] return 1;
+    #[cfg(not(unix))] return 2;
+}
+
+#[deny(warnings)]
+fn cfg_let_and_return() -> i32 {
+    #[cfg(unix)]
+    let x = 1;
+    #[cfg(not(unix))]
+    let x = 2;
+    x
+}
+
+fn main() {
+    cfg_return();
+    cfg_let_and_return();
+}