fix: redundant_test_prefix allow nested prefixed functions

Author: farazdagi

clippy_lints/src/redundant_test_prefix.rs

@@ -1,7 +1,7 @@
 use clippy_config::Conf;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::visitors::for_each_expr;
-use clippy_utils::{is_in_cfg_test, is_in_test_function};
+use clippy_utils::{is_in_cfg_test, is_test_function};
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::FnKind;
 use rustc_hir::{self as hir, Body, ExprKind, FnDecl};
@@ -65,21 +65,21 @@ impl<'tcx> LateLintPass<'tcx> for RedundantTestPrefix {
         _decl: &FnDecl<'_>,
         body: &'tcx Body<'_>,
         _span: Span,
-        _fn_def_id: LocalDefId,
+        fn_def_id: LocalDefId,
     ) {
+        // Ignore methods and closures.
+        let FnKind::ItemFn(ref ident, ..) = kind else {
+            return;
+        };
+
         // Skip the lint if the function is not within a node with `#[cfg(test)]` attribute,
         // which is true for integration tests. If the lint is enabled for integration tests,
         // via configuration value, ignore this check.
         if !(self.in_integration_tests || is_in_cfg_test(cx.tcx, body.id().hir_id)) {
             return;
         }
 
-        // Ignore methods and closures.
-        let FnKind::ItemFn(ref ident, ..) = kind else {
-            return;
-        };
-
-        if is_in_test_function(cx.tcx, body.id().hir_id) && ident.as_str().starts_with("test_") {
+        if is_test_function(cx.tcx, cx.tcx.local_def_id_to_hir_id(fn_def_id)) && ident.as_str().starts_with("test_") {
             let mut non_prefixed = ident.as_str().trim_start_matches("test_").to_string();
             let mut help_msg = "consider removing the `test_` prefix";
             // If `non_prefixed` conflicts with another function in the same module/scope,

clippy_utils/src/lib.rs

@@ -2685,6 +2685,28 @@ pub fn is_in_test_function(tcx: TyCtxt<'_>, id: HirId) -> bool {
     })
 }
 
+/// Checks if `id` has a `#[test]` attribute applied
+///
+/// This only checks directly applied attributes, to see if a node has a parent function marked with
+/// `#[test]` use [`is_in_test_function`].
+///
+/// Note: Add `//@compile-flags: --test` to UI tests with a `#[test]` function
+pub fn is_test_function(tcx: TyCtxt<'_>, id: HirId) -> bool {
+    with_test_item_names(tcx, tcx.parent_module(id), |names| {
+        let node = tcx.hir_node(id);
+        once((id, node)).any(|(_id, node)| {
+            if let Node::Item(item) = node {
+                if let ItemKind::Fn(_, _, _) = item.kind {
+                    // Note that we have sorted the item names in the visitor,
+                    // so the binary_search gets the same as `contains`, but faster.
+                    return names.binary_search(&item.ident.name).is_ok();
+                }
+            }
+            false
+        })
+    })
+}
+
 /// Checks if `id` has a `#[cfg(test)]` attribute applied
 ///
 /// This only checks directly applied attributes, to see if a node is inside a `#[cfg(test)]` parent

tests/ui/redundant_test_prefix.fixed

@@ -160,43 +160,52 @@ mod tests_no_annotations {
     }
 
     #[test]
-    fn test_foo() {
-    }
+    fn test_foo() {}
 
     #[test]
     fn test_foo_with_call() {
         main();
     }
 
     #[test]
-    fn test_f1() {
-    }
+    fn test_f1() {}
 
     #[test]
-    fn test_f2() {
-    }
+    fn test_f2() {}
 
     #[test]
-    fn test_f3() {
-    }
+    fn test_f3() {}
 
     #[test]
-    fn test_f4() {
-    }
+    fn test_f4() {}
 
     #[test]
-    fn test_f5() {
-    }
+    fn test_f5() {}
 
     #[test]
-    fn test_f6() {
-    }
+    fn test_f6() {}
 
     #[test]
-    fn test_f7() {
-    }
+    fn test_f7() {}
 
     #[test]
-    fn test_f8() {
+    fn test_f8() {}
+}
+
+// This test is inspired by real test in `clippy_utils/src/sugg.rs`.
+// The `is_in_test_function()` checks whether any identifier within a given node's parents is
+// marked with `#[test]` attribute. Thus flagging false positives when nested functions are
+// prefixed with `test_`. Therefore `is_test_function()` has been defined in `clippy_utils`,
+// allowing to select only functions that are immediately marked with `#[test]` annotation.
+//
+// This test case ensures that for such nested functions no error is emitted.
+#[test]
+fn not_op() {
+    fn test_not(foo: bool) {
+        assert!(foo);
     }
+
+    // Use helper function
+    test_not(true);
+    test_not(false);
 }

tests/ui/redundant_test_prefix.rs

@@ -160,43 +160,52 @@ mod tests_no_annotations {
     }
 
     #[test]
-    fn test_foo() {
-    }
+    fn test_foo() {}
 
     #[test]
     fn test_foo_with_call() {
         main();
     }
 
     #[test]
-    fn test_f1() {
-    }
+    fn test_f1() {}
 
     #[test]
-    fn test_f2() {
-    }
+    fn test_f2() {}
 
     #[test]
-    fn test_f3() {
-    }
+    fn test_f3() {}
 
     #[test]
-    fn test_f4() {
-    }
+    fn test_f4() {}
 
     #[test]
-    fn test_f5() {
-    }
+    fn test_f5() {}
 
     #[test]
-    fn test_f6() {
-    }
+    fn test_f6() {}
 
     #[test]
-    fn test_f7() {
-    }
+    fn test_f7() {}
 
     #[test]
-    fn test_f8() {
+    fn test_f8() {}
+}
+
+// This test is inspired by real test in `clippy_utils/src/sugg.rs`.
+// The `is_in_test_function()` checks whether any identifier within a given node's parents is
+// marked with `#[test]` attribute. Thus flagging false positives when nested functions are
+// prefixed with `test_`. Therefore `is_test_function()` has been defined in `clippy_utils`,
+// allowing to select only functions that are immediately marked with `#[test]` annotation.
+//
+// This test case ensures that for such nested functions no error is emitted.
+#[test]
+fn not_op() {
+    fn test_not(foo: bool) {
+        assert!(foo);
     }
+
+    // Use helper function
+    test_not(true);
+    test_not(false);
 }