Auto merge of rust-lang#8665 - InfRandomness:option_take_on_temporary, r=llogiq

Introduce needless_option_take lint

- \[x] Followed [lint naming conventions][lint_naming]
- \[x] Added passing UI tests (including committed `.stderr` file)
- \[x] `cargo test` passes locally
- \[x] Executed `cargo dev update_lints`
- \[x] Added lint documentation
- \[x] Run `cargo dev fmt`

Fixes rust-lang#8618

changelog: Introduce [`needless_option_take`] lint

Author: bors

CHANGELOG.md

@@ -3575,6 +3575,7 @@ 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

clippy_lints/src/lib.register_all.rs

@@ -184,6 +184,7 @@ 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),

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),

clippy_lints/src/lib.register_lints.rs

@@ -323,6 +323,7 @@ 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,

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 +2163,26 @@ declare_clippy_lint! {
     "use of `char::is_digit(..)` with literal radix of 10 or 16"
 }
 
+declare_clippy_lint! {
+    ///
+    /// ### Why is this bad?
+    ///
+    /// ### Example
+    /// ```rust
+    /// let x = Some(3);
+    /// x.as_ref().take();
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let x = Some(3);
+    /// x.as_ref();
+    /// ```
+    #[clippy::version = "1.61.0"]
+    pub NEEDLESS_OPTION_TAKE,
+    complexity,
+    "using `.as_ref().take()` on a temporary value"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2251,6 +2272,7 @@ 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 +2645,7 @@ 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);
             },

clippy_lints/src/methods/needless_option_take.rs

@@ -0,0 +1,41 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::match_def_path;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_span::sym;
+
+use super::NEEDLESS_OPTION_TAKE;
+
+pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, recv: &'tcx Expr<'_>) {
+    // Checks if expression type is equal to sym::Option and if the expr is not a syntactic place
+    if !recv.is_syntactic_place_expr() && is_expr_option(cx, recv) && has_expr_as_ref_path(cx, recv) {
+        let mut applicability = Applicability::MachineApplicable;
+        span_lint_and_sugg(
+            cx,
+            NEEDLESS_OPTION_TAKE,
+            expr.span,
+            "called `Option::take()` on a temporary value",
+            "try",
+            format!(
+                "{}",
+                snippet_with_applicability(cx, recv.span, "..", &mut applicability)
+            ),
+            applicability,
+        );
+    }
+}
+
+fn is_expr_option(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    let expr_type = cx.typeck_results().expr_ty(expr);
+    is_type_diagnostic_item(cx, expr_type, sym::Option)
+}
+
+fn has_expr_as_ref_path(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    if let Some(ref_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
+        return match_def_path(cx, ref_id, &["core", "option", "Option", "as_ref"]);
+    }
+    false
+}

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();
+}

tests/ui/needless_option_take.rs

@@ -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().take();
+}

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
+

tests/ui/option_take_on_temporary.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();
+}