Auto merge of rust-lang#12150 - ithinuel:add_misleading_use_of_ok, r=y21

Add lint for `unused_result_ok`

This PR adds a lint to capture the use of `expr.ok();` when the result is not _really_ used.

This could be interpreted as the result being checked (like it is with `unwrap()` or `expect`) but
it actually only ignores the result.

`let _ = expr;` expresses that intent better.

This was also mentionned in rust-lang#8994 (although not being the main topic of that issue).

changelog: [`misleading_use_of_ok`]: Add new lint to capture `.ok();` when the result is not _really_ used.

Author: bors

CHANGELOG.md

@@ -5999,6 +5999,7 @@ Released 2018-09-13
 [`unused_io_amount`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_io_amount
 [`unused_label`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_label
 [`unused_peekable`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_peekable
+[`unused_result_ok`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_result_ok
 [`unused_rounding`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_rounding
 [`unused_self`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_self
 [`unused_unit`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_unit

clippy_dev/src/update_lints.rs

@@ -372,14 +372,14 @@ fn remove_lint_declaration(name: &str, path: &Path, lints: &mut Vec<Lint>) -> io
 
         // Some lints have their own directories, delete them
         if path.is_dir() {
-            fs::remove_dir_all(path).ok();
+            let _ = fs::remove_dir_all(path);
             return;
         }
 
         // Remove all related test files
-        fs::remove_file(path.with_extension("rs")).ok();
-        fs::remove_file(path.with_extension("stderr")).ok();
-        fs::remove_file(path.with_extension("fixed")).ok();
+        let _ = fs::remove_file(path.with_extension("rs"));
+        let _ = fs::remove_file(path.with_extension("stderr"));
+        let _ = fs::remove_file(path.with_extension("fixed"));
     }
 
     fn remove_impl_lint_pass(lint_name_upper: &str, content: &mut String) {
@@ -422,7 +422,7 @@ fn remove_lint_declaration(name: &str, path: &Path, lints: &mut Vec<Lint>) -> io
                     lint_mod_path.set_file_name(name);
                     lint_mod_path.set_extension("rs");
 
-                    fs::remove_file(lint_mod_path).ok();
+                    let _ = fs::remove_file(lint_mod_path);
                 }
 
                 let mut content =

clippy_lints/src/declared_lints.rs

@@ -739,6 +739,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::unused_async::UNUSED_ASYNC_INFO,
     crate::unused_io_amount::UNUSED_IO_AMOUNT_INFO,
     crate::unused_peekable::UNUSED_PEEKABLE_INFO,
+    crate::unused_result_ok::UNUSED_RESULT_OK_INFO,
     crate::unused_rounding::UNUSED_ROUNDING_INFO,
     crate::unused_self::UNUSED_SELF_INFO,
     crate::unused_unit::UNUSED_UNIT_INFO,

clippy_lints/src/lib.rs

@@ -370,6 +370,7 @@ mod unsafe_removed_from_name;
 mod unused_async;
 mod unused_io_amount;
 mod unused_peekable;
+mod unused_result_ok;
 mod unused_rounding;
 mod unused_self;
 mod unused_unit;
@@ -671,6 +672,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(missing_doc::MissingDoc::new(conf)));
     store.register_late_pass(|_| Box::new(missing_inline::MissingInline));
     store.register_late_pass(move |_| Box::new(exhaustive_items::ExhaustiveItems));
+    store.register_late_pass(|_| Box::new(unused_result_ok::UnusedResultOk));
     store.register_late_pass(|_| Box::new(match_result_ok::MatchResultOk));
     store.register_late_pass(|_| Box::new(partialeq_ne_impl::PartialEqNeImpl));
     store.register_late_pass(|_| Box::new(unused_io_amount::UnusedIoAmount));

clippy_lints/src/unused_result_ok.rs

@@ -0,0 +1,59 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_context;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_errors::Applicability;
+use rustc_hir::{ExprKind, Stmt, StmtKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::declare_lint_pass;
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for calls to `Result::ok()` without using the returned `Option`.
+    ///
+    /// ### Why is this bad?
+    /// Using `Result::ok()` may look like the result is checked like `unwrap` or `expect` would do
+    /// but it only silences the warning caused by `#[must_use]` on the `Result`.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// # fn some_function() -> Result<(), ()> { Ok(()) }
+    /// some_function().ok();
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// # fn some_function() -> Result<(), ()> { Ok(()) }
+    /// let _ = some_function();
+    /// ```
+    #[clippy::version = "1.70.0"]
+    pub UNUSED_RESULT_OK,
+    restriction,
+    "Use of `.ok()` to silence `Result`'s `#[must_use]` is misleading. Use `let _ =` instead."
+}
+declare_lint_pass!(UnusedResultOk => [UNUSED_RESULT_OK]);
+
+impl LateLintPass<'_> for UnusedResultOk {
+    fn check_stmt(&mut self, cx: &LateContext<'_>, stmt: &Stmt<'_>) {
+        if let StmtKind::Semi(expr) = stmt.kind
+            && let ExprKind::MethodCall(ok_path, recv, [], ..) = expr.kind //check is expr.ok() has type Result<T,E>.ok(, _)
+            && ok_path.ident.as_str() == "ok"
+            && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result)
+            && !in_external_macro(cx.sess(), stmt.span)
+        {
+            let ctxt = expr.span.ctxt();
+            let mut applicability = Applicability::MaybeIncorrect;
+            let snippet = snippet_with_context(cx, recv.span, ctxt, "", &mut applicability).0;
+            let sugg = format!("let _ = {snippet}");
+            span_lint_and_sugg(
+                cx,
+                UNUSED_RESULT_OK,
+                expr.span,
+                "ignoring a result with `.ok()` is misleading",
+                "consider using `let _ =` and removing the call to `.ok()` instead",
+                sugg,
+                applicability,
+            );
+        }
+    }
+}

tests/ui/unused_result_ok.fixed

@@ -0,0 +1,40 @@
+//@aux-build:proc_macros.rs
+#![warn(clippy::unused_result_ok)]
+#![allow(dead_code)]
+
+#[macro_use]
+extern crate proc_macros;
+
+fn bad_style(x: &str) {
+    let _ = x.parse::<u32>();
+}
+
+fn good_style(x: &str) -> Option<u32> {
+    x.parse::<u32>().ok()
+}
+
+#[rustfmt::skip]
+fn strange_parse(x: &str) {
+    let _ = x   .   parse::<i32>();
+}
+
+macro_rules! v {
+    () => {
+        Ok::<(), ()>(())
+    };
+}
+
+macro_rules! w {
+    () => {
+        let _ = Ok::<(), ()>(());
+    };
+}
+
+fn main() {
+    let _ = v!();
+    w!();
+
+    external! {
+        Ok::<(),()>(()).ok();
+    };
+}

tests/ui/unused_result_ok.rs

@@ -0,0 +1,40 @@
+//@aux-build:proc_macros.rs
+#![warn(clippy::unused_result_ok)]
+#![allow(dead_code)]
+
+#[macro_use]
+extern crate proc_macros;
+
+fn bad_style(x: &str) {
+    x.parse::<u32>().ok();
+}
+
+fn good_style(x: &str) -> Option<u32> {
+    x.parse::<u32>().ok()
+}
+
+#[rustfmt::skip]
+fn strange_parse(x: &str) {
+    x   .   parse::<i32>()   .   ok   ();
+}
+
+macro_rules! v {
+    () => {
+        Ok::<(), ()>(())
+    };
+}
+
+macro_rules! w {
+    () => {
+        Ok::<(), ()>(()).ok();
+    };
+}
+
+fn main() {
+    v!().ok();
+    w!();
+
+    external! {
+        Ok::<(),()>(()).ok();
+    };
+}

tests/ui/unused_result_ok.stderr

@@ -0,0 +1,52 @@
+error: ignoring a result with `.ok()` is misleading
+  --> tests/ui/unused_result_ok.rs:9:5
+   |
+LL |     x.parse::<u32>().ok();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::unused-result-ok` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unused_result_ok)]`
+help: consider using `let _ =` and removing the call to `.ok()` instead
+   |
+LL |     let _ = x.parse::<u32>();
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: ignoring a result with `.ok()` is misleading
+  --> tests/ui/unused_result_ok.rs:18:5
+   |
+LL |     x   .   parse::<i32>()   .   ok   ();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: consider using `let _ =` and removing the call to `.ok()` instead
+   |
+LL |     let _ = x   .   parse::<i32>();
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: ignoring a result with `.ok()` is misleading
+  --> tests/ui/unused_result_ok.rs:34:5
+   |
+LL |     v!().ok();
+   |     ^^^^^^^^^
+   |
+help: consider using `let _ =` and removing the call to `.ok()` instead
+   |
+LL |     let _ = v!();
+   |     ~~~~~~~~~~~~
+
+error: ignoring a result with `.ok()` is misleading
+  --> tests/ui/unused_result_ok.rs:29:9
+   |
+LL |         Ok::<(), ()>(()).ok();
+   |         ^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     w!();
+   |     ---- in this macro invocation
+   |
+   = note: this error originates in the macro `w` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider using `let _ =` and removing the call to `.ok()` instead
+   |
+LL |         let _ = Ok::<(), ()>(());
+   |         ~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 4 previous errors
+