Add lint for misleading_use_of_ok

Author: ithinuel

CHANGELOG.md

@@ -5347,6 +5347,7 @@ Released 2018-09-13
 [`min_ident_chars`]: https://rust-lang.github.io/rust-clippy/master/index.html#min_ident_chars
 [`min_max`]: https://rust-lang.github.io/rust-clippy/master/index.html#min_max
 [`misaligned_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#misaligned_transmute
+[`misleading_use_of_ok`]: https://rust-lang.github.io/rust-clippy/master/index.html#misleading_use_of_ok
 [`mismatched_target_os`]: https://rust-lang.github.io/rust-clippy/master/index.html#mismatched_target_os
 [`mismatching_type_param_order`]: https://rust-lang.github.io/rust-clippy/master/index.html#mismatching_type_param_order
 [`misnamed_getters`]: https://rust-lang.github.io/rust-clippy/master/index.html#misnamed_getters

clippy_dev/src/update_lints.rs

@@ -377,14 +377,14 @@ 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) {
@@ -427,7 +427,7 @@ 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

@@ -477,6 +477,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::misc_early::UNNEEDED_WILDCARD_PATTERN_INFO,
     crate::misc_early::UNSEPARATED_LITERAL_SUFFIX_INFO,
     crate::misc_early::ZERO_PREFIXED_LITERAL_INFO,
+    crate::misleading_use_of_ok::MISLEADING_USE_OF_OK_INFO,
     crate::mismatching_type_param_order::MISMATCHING_TYPE_PARAM_ORDER_INFO,
     crate::missing_assert_message::MISSING_ASSERT_MESSAGE_INFO,
     crate::missing_asserts_for_indexing::MISSING_ASSERTS_FOR_INDEXING_INFO,

clippy_lints/src/lib.rs

@@ -212,6 +212,7 @@ mod min_ident_chars;
 mod minmax;
 mod misc;
 mod misc_early;
+mod misleading_use_of_ok;
 mod mismatching_type_param_order;
 mod missing_assert_message;
 mod missing_asserts_for_indexing;
@@ -765,6 +766,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(missing_doc::MissingDoc::new(missing_docs_in_crate_items)));
     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(misleading_use_of_ok::MisleadingUseOfOk));
     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/misleading_use_of_ok.rs

@@ -0,0 +1,57 @@
+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};
+use rustc_session::declare_lint_pass;
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for `Result::ok();` when the result is not captured.
+    ///
+    /// ### 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 MISLEADING_USE_OF_OK,
+    style,
+    "Use of `.ok()` to silence `Result`'s `#[must_use]` is misleading. Use `let _ =` instead."
+}
+declare_lint_pass!(MisleadingUseOfOk => [MISLEADING_USE_OF_OK]);
+
+impl LateLintPass<'_> for MisleadingUseOfOk {
+    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)
+        {
+            let ctxt = expr.span.ctxt();
+            let mut applicability = Applicability::MachineApplicable;
+            let trimmed_ok = snippet_with_context(cx, recv.span, ctxt, "", &mut applicability).0;
+            let sugg = format!("let _ = {}", trimmed_ok.trim().trim_end_matches('.'),);
+            span_lint_and_sugg(
+                cx,
+                MISLEADING_USE_OF_OK,
+                expr.span,
+                "ignoring a result with `.ok()` is misleading",
+                "consider using `let _ =` and removing the call to `.ok()` instead",
+                sugg,
+                applicability,
+            );
+        }
+    }
+}

tests/ui/misleading_use_of_ok.fixed

@@ -0,0 +1,17 @@
+#![warn(clippy::misleading_use_of_ok)]
+#![allow(dead_code)]
+
+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>();
+}
+
+fn main() {}

tests/ui/misleading_use_of_ok.rs

@@ -0,0 +1,17 @@
+#![warn(clippy::misleading_use_of_ok)]
+#![allow(dead_code)]
+
+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   ();
+}
+
+fn main() {}

tests/ui/misleading_use_of_ok.stderr

@@ -0,0 +1,26 @@
+error: ignoring a result with `.ok()` is misleading
+  --> $DIR/misleading_use_of_ok.rs:5:5
+   |
+LL |     x.parse::<u32>().ok();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::misleading-use-of-ok` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::misleading_use_of_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
+  --> $DIR/misleading_use_of_ok.rs:14:5
+   |
+LL |     x   .   parse::<i32>()   .   ok   ();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: consider using `let _ =` and removing the call to `.ok()` instead
+   |
+LL |     let _ = x   .   parse::<i32>();
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 2 previous errors
+