Introduce option_take_on_temporary lints

This lint checks if Option::take() is used on a temporary value (a value
that is not of type &mut Option and that is not a Place expression) to
suggest omitting take()

Author: b-NC

CHANGELOG.md

@@ -3504,6 +3504,7 @@ Released 2018-09-13
 [`option_map_or_none`]: https://rust-lang.github.io/rust-clippy/master/index.html#option_map_or_none
 [`option_map_unit_fn`]: https://rust-lang.github.io/rust-clippy/master/index.html#option_map_unit_fn
 [`option_option`]: https://rust-lang.github.io/rust-clippy/master/index.html#option_option
+[`option_take_on_temporary`]: https://rust-lang.github.io/rust-clippy/master/index.html#option_take_on_temporary
 [`or_fun_call`]: https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call
 [`or_then_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#or_then_unwrap
 [`out_of_bounds_indexing`]: https://rust-lang.github.io/rust-clippy/master/index.html#out_of_bounds_indexing

clippy_lints/src/lib.register_all.rs

@@ -188,6 +188,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(methods::OPTION_AS_REF_DEREF),
     LintId::of(methods::OPTION_FILTER_MAP),
     LintId::of(methods::OPTION_MAP_OR_NONE),
+    LintId::of(methods::OPTION_TAKE_ON_TEMPORARY),
     LintId::of(methods::OR_FUN_CALL),
     LintId::of(methods::OR_THEN_UNWRAP),
     LintId::of(methods::RESULT_MAP_OR_INTO_OPTION),

clippy_lints/src/lib.register_lints.rs

@@ -327,6 +327,7 @@ store.register_lints(&[
     methods::OPTION_AS_REF_DEREF,
     methods::OPTION_FILTER_MAP,
     methods::OPTION_MAP_OR_NONE,
+    methods::OPTION_TAKE_ON_TEMPORARY,
     methods::OR_FUN_CALL,
     methods::OR_THEN_UNWRAP,
     methods::RESULT_MAP_OR_INTO_OPTION,

clippy_lints/src/lib.register_suspicious.rs

@@ -22,6 +22,7 @@ store.register_group(true, "clippy::suspicious", Some("clippy_suspicious"), vec!
     LintId::of(loops::EMPTY_LOOP),
     LintId::of(loops::FOR_LOOPS_OVER_FALLIBLES),
     LintId::of(loops::MUT_RANGE_BOUND),
+    LintId::of(methods::OPTION_TAKE_ON_TEMPORARY),
     LintId::of(methods::SUSPICIOUS_MAP),
     LintId::of(mut_key::MUTABLE_KEY_TYPE),
     LintId::of(octal_escapes::OCTAL_ESCAPES),

clippy_lints/src/methods/mod.rs

@@ -46,6 +46,7 @@ mod ok_expect;
 mod option_as_ref_deref;
 mod option_map_or_none;
 mod option_map_unwrap_or;
+mod option_take_on_temporary;
 mod or_fun_call;
 mod or_then_unwrap;
 mod search_is_some;
@@ -2131,6 +2132,24 @@ declare_clippy_lint! {
     "no-op use of `deref` or `deref_mut` method to `Option`."
 }
 
+declare_clippy_lint! {
+    ///
+    /// ### Why is this bad?
+    ///
+    /// ### Example
+    /// ```rust
+    /// // example code where clippy issues a warning
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // example code which does not raise clippy warning
+    /// ```
+    #[clippy::version = "1.61.0"]
+    pub OPTION_TAKE_ON_TEMPORARY,
+    suspicious,
+    "using `.as_ref().take()` on a temporary value"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2219,6 +2238,7 @@ impl_lint_pass!(Methods => [
     UNNECESSARY_JOIN,
     ERR_EXPECT,
     NEEDLESS_OPTION_AS_DEREF,
+    OPTION_TAKE_ON_TEMPORARY,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -2595,6 +2615,7 @@ fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Optio
                     }
                 }
             },
+            ("take", []) => option_take_on_temporary::check(cx, expr, recv),
             ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
                 implicit_clone::check(cx, name, expr, recv);
             },

clippy_lints/src/methods/option_take_on_temporary.rs

@@ -0,0 +1,23 @@
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_span::sym::Result as sym_result;
+
+use super::OPTION_TAKE_ON_TEMPORARY;
+
+pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, recv: &'tcx Expr<'_>) {
+    if_chain! {
+        if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym_result);
+        let result_type = cx.typeck_results().expr_ty(recv);
+
+        then {
+            span_lint(
+                cx,
+                OPTION_TAKE_ON_TEMPORARY,
+                expr.span,
+                "Format test"
+            );
+        }
+    };
+}

tests/ui/option_take_on_temporary.rs

@@ -0,0 +1,5 @@
+fn main() {
+    println!("Testing option_take_on_temporary");
+    let x = Some(3);
+    let y = x.as_ref().take();
+}