FIX: NegMultiply should preserve parenthesis when method is called (#15179)

Hi,

I noticed that the lint
[neg_multiply](https://rust-lang.github.io/rust-clippy/master/index.html#neg_multiply)
generates bad code when we call a method on the expression.
Consider `((a.delta - 0.5).abs() * -1.0).total_cmp(&1.0)`. Currently
this would be changed by clippy to `-(a.delta - 0.5).abs()
.total_cmp(&1.0)` - which does not compile because we are trying to
negate an ordering enum - but what we really want is `(-(a.delta -
0.5).abs()).total_cmp(&1.0)`.

This PR fixes this.

changelog: [`neg_multiply`] does not remove parenthesis anymore if a
method is being called on the affected expression

NOTE: This is the first time I am contributing to clippy or the rust
repo in general. So I am not sure whether my approach to fixing this
issue is goo, if there are better solutions or if I missed something.

Thanks & hope you have a good day,
Dario

3 files changed, 31 insertions, 1 deletions

diff --git a/tests/ui/neg_multiply.fixed b/tests/ui/neg_multiply.fixed
index ff6e08300e2..32d466e88fc 100644
--- a/tests/ui/neg_multiply.fixed
+++ b/tests/ui/neg_multiply.fixed
@@ -82,3 +82,15 @@ fn float() {
 
     -1.0 * -1.0; // should be ok
 }
+
+struct Y {
+    delta: f64,
+}
+
+fn nested() {
+    let a = Y { delta: 1.0 };
+    let b = Y { delta: 1.0 };
+    let _ = (-(a.delta - 0.5).abs()).total_cmp(&1.0);
+    //~^ neg_multiply
+    let _ = (-(a.delta - 0.5).abs()).total_cmp(&1.0);
+}
diff --git a/tests/ui/neg_multiply.rs b/tests/ui/neg_multiply.rs
index b0f4e85c78e..241a72c6d99 100644
--- a/tests/ui/neg_multiply.rs
+++ b/tests/ui/neg_multiply.rs
@@ -82,3 +82,15 @@ fn float() {
 
     -1.0 * -1.0; // should be ok
 }
+
+struct Y {
+    delta: f64,
+}
+
+fn nested() {
+    let a = Y { delta: 1.0 };
+    let b = Y { delta: 1.0 };
+    let _ = ((a.delta - 0.5).abs() * -1.0).total_cmp(&1.0);
+    //~^ neg_multiply
+    let _ = (-(a.delta - 0.5).abs()).total_cmp(&1.0);
+}
diff --git a/tests/ui/neg_multiply.stderr b/tests/ui/neg_multiply.stderr
index 2ef7e32ce05..f4fb6d3ce54 100644
--- a/tests/ui/neg_multiply.stderr
+++ b/tests/ui/neg_multiply.stderr
@@ -97,5 +97,11 @@ error: this multiplication by -1 can be written more succinctly
 LL |     (3.0_f32 as f64) * -1.0;
    |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `-(3.0_f32 as f64)`
 
-error: aborting due to 16 previous errors
+error: this multiplication by -1 can be written more succinctly
+  --> tests/ui/neg_multiply.rs:93:13
+   |
+LL |     let _ = ((a.delta - 0.5).abs() * -1.0).total_cmp(&1.0);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `(-(a.delta - 0.5).abs())`
+
+error: aborting due to 17 previous errors