allow needless_option_take to report for more cases

In general, needless_option_take should report whenever
take() is called on a temporary value, not just when the
temporary value is created by as_ref()

Author: ericwu17

clippy_lints/src/methods/needless_option_take.rs

@@ -1,30 +1,24 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::match_def_path;
-use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::diagnostics::span_lint_and_note;
 use clippy_utils::ty::is_type_diagnostic_item;
-use rustc_errors::Applicability;
-use rustc_hir::Expr;
+use rustc_hir::{Expr, ExprKind, QPath};
 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,
-        );
+    if !recv.is_syntactic_place_expr() && is_expr_option(cx, recv) {
+        if let Some(function_name) = is_creating_temporary_value(recv) {
+            span_lint_and_note(
+                cx,
+                NEEDLESS_OPTION_TAKE,
+                expr.span,
+                "called `Option::take()` on a temporary value",
+                Some(recv.span),
+                format!("`{}` creates a temporary value", function_name),
+            );
+        }
     }
 }
 
@@ -33,9 +27,24 @@ fn is_expr_option(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     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"]);
+fn is_creating_temporary_value<'a>(expr: &'a Expr<'_>) -> Option<&'a str> {
+    // Returns the string of the function call that creates the temporary.
+    // When this function is called, we are reasonably certain that the ExprKind is either
+    // Call or MethodCall because we already checked that the expression is not
+    // is_syntactic_place_expr().
+    match expr.peel_borrows().kind {
+        ExprKind::Call(function, _) => {
+            if let ExprKind::Path(QPath::Resolved(_, func_path)) = function.kind {
+                if func_path.segments.len() > 0 {
+                    return Some(func_path.segments[0].ident.name.as_str());
+                }
+            }
+            if let ExprKind::Path(QPath::TypeRelative(_, func_path_segment)) = function.kind {
+                return Some(func_path_segment.ident.name.as_str());
+            }
+            None
+        },
+        ExprKind::MethodCall(path_segment, ..) => Some(path_segment.ident.name.as_str()),
+        _ => None,
     }
-    false
 }

tests/ui/needless_option_take.fixed

@@ -1,3 +1,15 @@
+struct MyStruct;
+
+impl MyStruct {
+    pub fn get_option() -> Option<Self> {
+        todo!()
+    }
+}
+
+fn return_option() -> Option<i32> {
+    todo!()
+}
+
 fn main() {
     println!("Testing non erroneous option_take_on_temporary");
     let mut option = Some(1);
@@ -7,7 +19,40 @@ fn main() {
     let x = Some(3);
     x.as_ref();
 
-    println!("Testing erroneous option_take_on_temporary");
     let x = Some(3);
     x.as_ref().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    println!("Testing non erroneous option_take_on_temporary");
+    let mut x = Some(3);
+    let y = x.as_mut();
+
+    let mut x = Some(3);
+    let y = x.as_mut().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+    let y = x.replace(289).take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let y = Some(3).as_mut().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let y = Option::as_mut(&mut x).take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let x = return_option();
+    let x = return_option().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let x = MyStruct::get_option();
+    let x = MyStruct::get_option().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let mut my_vec = vec![1, 2, 3];
+    my_vec.push(4);
+    let y = my_vec.first();
+    let y = my_vec.first().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
+
+    let y = my_vec.first().take();
+    //~^ ERROR: called `Option::take()` on a temporary value
 }

tests/ui/needless_option_take.rs

@@ -1,11 +1,112 @@
 error: called `Option::take()` on a temporary value
-  --> tests/ui/needless_option_take.rs:12:5
+  --> tests/ui/needless_option_take.rs:23:5
    |
 LL |     x.as_ref().take();
-   |     ^^^^^^^^^^^^^^^^^ help: try: `x.as_ref()`
+   |     ^^^^^^^^^^^^^^^^^
    |
+note: `as_ref` creates a temporary value
+  --> tests/ui/needless_option_take.rs:23:5
+   |
+LL |     x.as_ref().take();
+   |     ^^^^^^^^^^
    = note: `-D clippy::needless-option-take` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_option_take)]`
 
-error: aborting due to 1 previous error
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:31:13
+   |
+LL |     let y = x.as_mut().take();
+   |             ^^^^^^^^^^^^^^^^^
+   |
+note: `as_mut` creates a temporary value
+  --> tests/ui/needless_option_take.rs:31:13
+   |
+LL |     let y = x.as_mut().take();
+   |             ^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:33:13
+   |
+LL |     let y = x.replace(289).take();
+   |             ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `replace` creates a temporary value
+  --> tests/ui/needless_option_take.rs:33:13
+   |
+LL |     let y = x.replace(289).take();
+   |             ^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:36:13
+   |
+LL |     let y = Some(3).as_mut().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `as_mut` creates a temporary value
+  --> tests/ui/needless_option_take.rs:36:13
+   |
+LL |     let y = Some(3).as_mut().take();
+   |             ^^^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:39:13
+   |
+LL |     let y = Option::as_mut(&mut x).take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `as_mut` creates a temporary value
+  --> tests/ui/needless_option_take.rs:39:13
+   |
+LL |     let y = Option::as_mut(&mut x).take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:43:13
+   |
+LL |     let x = return_option().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `return_option` creates a temporary value
+  --> tests/ui/needless_option_take.rs:43:13
+   |
+LL |     let x = return_option().take();
+   |             ^^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:47:13
+   |
+LL |     let x = MyStruct::get_option().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `get_option` creates a temporary value
+  --> tests/ui/needless_option_take.rs:47:13
+   |
+LL |     let x = MyStruct::get_option().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:53:13
+   |
+LL |     let y = my_vec.first().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `first` creates a temporary value
+  --> tests/ui/needless_option_take.rs:53:13
+   |
+LL |     let y = my_vec.first().take();
+   |             ^^^^^^^^^^^^^^
+
+error: called `Option::take()` on a temporary value
+  --> tests/ui/needless_option_take.rs:56:13
+   |
+LL |     let y = my_vec.first().take();
+   |             ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `first` creates a temporary value
+  --> tests/ui/needless_option_take.rs:56:13
+   |
+LL |     let y = my_vec.first().take();
+   |             ^^^^^^^^^^^^^^
+
+error: aborting due to 9 previous errors