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()

10 files changed, 79 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 858547c84c1..d4096ca89df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3473,6 +3473,7 @@ Released 2018-09-13
 [`needless_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
 [`needless_match`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_match
 [`needless_option_as_deref`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_option_as_deref
+[`needless_option_take`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_option_take
 [`needless_pass_by_value`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_value
 [`needless_question_mark`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_question_mark
 [`needless_range_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_range_loop
diff --git a/clippy_lints/src/lib.register_all.rs b/clippy_lints/src/lib.register_all.rs
index 52c440de9dd..84e3176c003 100644
--- a/clippy_lints/src/lib.register_all.rs
+++ b/clippy_lints/src/lib.register_all.rs
@@ -183,6 +183,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(methods::MAP_FLATTEN),
     LintId::of(methods::MAP_IDENTITY),
     LintId::of(methods::NEEDLESS_OPTION_AS_DEREF),
+    LintId::of(methods::NEEDLESS_OPTION_TAKE),
     LintId::of(methods::NEEDLESS_SPLITN),
     LintId::of(methods::NEW_RET_NO_SELF),
     LintId::of(methods::OK_EXPECT),
diff --git a/clippy_lints/src/lib.register_complexity.rs b/clippy_lints/src/lib.register_complexity.rs
index 10369a855ae..2f6ebd445eb 100644
--- a/clippy_lints/src/lib.register_complexity.rs
+++ b/clippy_lints/src/lib.register_complexity.rs
@@ -45,6 +45,7 @@ store.register_group(true, "clippy::complexity", Some("clippy_complexity"), vec!
     LintId::of(methods::MAP_FLATTEN),
     LintId::of(methods::MAP_IDENTITY),
     LintId::of(methods::NEEDLESS_OPTION_AS_DEREF),
+    LintId::of(methods::NEEDLESS_OPTION_TAKE),
     LintId::of(methods::NEEDLESS_SPLITN),
     LintId::of(methods::OPTION_AS_REF_DEREF),
     LintId::of(methods::OPTION_FILTER_MAP),
diff --git a/clippy_lints/src/lib.register_lints.rs b/clippy_lints/src/lib.register_lints.rs
index cfaa6871b50..aa9435f3b59 100644
--- a/clippy_lints/src/lib.register_lints.rs
+++ b/clippy_lints/src/lib.register_lints.rs
@@ -322,6 +322,7 @@ store.register_lints(&[
     methods::MAP_IDENTITY,
     methods::MAP_UNWRAP_OR,
     methods::NEEDLESS_OPTION_AS_DEREF,
+    methods::NEEDLESS_OPTION_TAKE,
     methods::NEEDLESS_SPLITN,
     methods::NEW_RET_NO_SELF,
     methods::OK_EXPECT,
diff --git a/clippy_lints/src/lib.register_suspicious.rs b/clippy_lints/src/lib.register_suspicious.rs
index 82f45b5fd58..6588ca4a4a7 100644
--- a/clippy_lints/src/lib.register_suspicious.rs
+++ b/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),
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 82f4769a699..3d4c193691a 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -43,6 +43,7 @@ mod map_flatten;
 mod map_identity;
 mod map_unwrap_or;
 mod needless_option_as_deref;
+mod needless_option_take;
 mod ok_expect;
 mod option_as_ref_deref;
 mod option_map_or_none;
@@ -2162,6 +2163,24 @@ declare_clippy_lint! {
     "use of `char::is_digit(..)` with literal radix of 10 or 16"
 }
 
+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 NEEDLESS_OPTION_TAKE,
+    suspicious,
+    "using `.as_ref().take()` on a temporary value"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2251,6 +2270,7 @@ impl_lint_pass!(Methods => [
     ERR_EXPECT,
     NEEDLESS_OPTION_AS_DEREF,
     IS_DIGIT_ASCII_RADIX,
+    NEEDLESS_OPTION_TAKE,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -2623,6 +2643,7 @@ fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Optio
                     }
                 }
             },
+            ("take", []) => needless_option_take::check(cx, expr, recv),
             ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
                 implicit_clone::check(cx, name, expr, recv);
             },
diff --git a/clippy_lints/src/methods/needless_option_take.rs b/clippy_lints/src/methods/needless_option_take.rs
new file mode 100644
index 00000000000..b3696273e1d
--- /dev/null
+++ b/clippy_lints/src/methods/needless_option_take.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::NEEDLESS_OPTION_TAKE;
+
+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,
+                NEEDLESS_OPTION_TAKE,
+                expr.span,
+                "Format test"
+            );
+        }
+    };
+}
diff --git a/tests/ui/needless_option_take.fixed b/tests/ui/needless_option_take.fixed
new file mode 100644
index 00000000000..29691e81666
--- /dev/null
+++ b/tests/ui/needless_option_take.fixed
@@ -0,0 +1,15 @@
+// run-rustfix
+
+fn main() {
+    println!("Testing non erroneous option_take_on_temporary");
+    let mut option = Some(1);
+    let _ = Box::new(move || option.take().unwrap());
+
+    println!("Testing non erroneous option_take_on_temporary");
+    let x = Some(3);
+    x.as_ref();
+
+    println!("Testing erroneous option_take_on_temporary");
+    let x = Some(3);
+    x.as_ref();
+}
diff --git a/tests/ui/needless_option_take.rs b/tests/ui/needless_option_take.rs
new file mode 100644
index 00000000000..2b32b9467f5
--- /dev/null
+++ b/tests/ui/needless_option_take.rs
@@ -0,0 +1,5 @@
+fn main() {
+    println!("Testing option_take_on_temporary");
+    let x = Some(3);
+    let y = x.as_ref().take();
+}
diff --git a/tests/ui/needless_option_take.stderr b/tests/ui/needless_option_take.stderr
new file mode 100644
index 00000000000..cb3bf015b36
--- /dev/null
+++ b/tests/ui/needless_option_take.stderr
@@ -0,0 +1,10 @@
+error: called `Option::take()` on a temporary value
+  --> $DIR/needless_option_take.rs:14:5
+   |
+LL |     x.as_ref().take();
+   |     ^^^^^^^^^^^^^^^^^ help: try: `x.as_ref()`
+   |
+   = note: `-D clippy::needless-option-take` implied by `-D warnings`
+
+error: aborting due to previous error
+