Lint closures that only bind other args with no other expressions

Author: Yusuf Raji

clippy_lints/src/single_option_map.rs

@@ -58,8 +58,25 @@ impl<'tcx> LateLintPass<'tcx> for SingleOptionMap {
                 && is_type_diagnostic_item(cx, callee_type, sym::Option)
                 && let ExprKind::Path(_path) = callee.kind
                 && let Res::Local(_id) = path_res(cx, callee)
+                && matches!(path_res(cx, callee), Res::Local(_id))
                 && !matches!(args[0].kind, ExprKind::Path(_))
             {
+                if let ExprKind::Closure(closure) = args[0].kind {
+                    let Body { params: [..], value } = cx.tcx.hir().body(closure.body);
+                    if let ExprKind::Call(func, f_args) = value.kind
+                        && matches!(func.kind, ExprKind::Path(_))
+                        && f_args.iter().all(|arg| matches!(arg.kind, ExprKind::Path(_)))
+                    {
+                        return;
+                    } else if let ExprKind::MethodCall(_segment, receiver, method_args, _span) = value.kind
+                        && matches!(receiver.kind, ExprKind::Path(_))
+                        && method_args.iter().all(|arg| matches!(arg.kind, ExprKind::Path(_)))
+                        && method_args.iter().all(|arg| matches!(path_res(cx, arg), Res::Local(_)))
+                    {
+                        return;
+                    }
+                }
+
                 span_lint_and_help(
                     cx,
                     SINGLE_OPTION_MAP,

tests/ui/single_option_map.rs

@@ -40,6 +40,16 @@ fn manipulate_opt_explicit(opt_i: Option<i32>) -> Option<i32> {
     opt_i.map(|x| manipulate(x))
 }
 
+// No lint
+fn multi_args(a: String, b: bool, c: u64) -> String {
+    a
+}
+
+// No lint: contains only map of a closure that binds other arguments
+fn multi_args_opt(a: Option<String>, b: bool, c: u64) -> Option<String> {
+    a.map(|a| multi_args(a, b, c))
+}
+
 fn main() {
     let answer = Some(42u32);
     let h_result = h(answer);

tests/ui/single_option_map.stderr

@@ -22,15 +22,5 @@ LL | | }
    |
    = help: move the `.map` to the caller or to an `_opt` function
 
-error: `fn` that only maps over argument
-  --> tests/ui/single_option_map.rs:39:1
-   |
-LL | / fn manipulate_opt_explicit(opt_i: Option<i32>) -> Option<i32> {
-LL | |     opt_i.map(|x| manipulate(x))
-LL | | }
-   | |_^
-   |
-   = help: move the `.map` to the caller or to an `_opt` function
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors