Auto merge of rust-lang#11385 - markhuang1212:master, r=blyxyas

skip float_cmp check if lhs is a custom type

*Please write a short comment explaining your change (or "none" for internal only changes)*

changelog: [`float_cmp`]: allow float eq comparison when lhs is a custom type that implements PartialEq<f32/f64>

If the lhs of a comparison is not float, it means there is a user implemented PartialEq, and the caller is invoking that custom version of `==`, instead of the default floating point equal comparison.

People may wrap f32 with a struct (say `MyF32`) and implement its PartialEq that will do the `is_close()` check, so that `MyF32` can be compared with either f32 or `MyF32`.

clippy_lints/src/operators/float_cmp.rs

@@ -17,7 +17,7 @@ pub(crate) fn check<'tcx>(
     left: &'tcx Expr<'_>,
     right: &'tcx Expr<'_>,
 ) {
-    if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
+    if (op == BinOpKind::Eq || op == BinOpKind::Ne) && is_float(cx, left) {
         let left_is_local = match constant_with_source(cx, cx.typeck_results(), left) {
             Some((c, s)) if !is_allowed(&c) => s.is_local(),
             Some(_) => return,

tests/ui/float_cmp.rs

@@ -41,13 +41,26 @@ impl PartialEq for X {
     }
 }
 
+impl PartialEq<f32> for X {
+    fn eq(&self, o: &f32) -> bool {
+        if self.val.is_nan() {
+            o.is_nan()
+        } else {
+            self.val == *o // no error, inside "eq" fn
+        }
+    }
+}
+
 fn main() {
     ZERO == 0f32; //no error, comparison with zero is ok
     1.0f32 != f32::INFINITY; // also comparison with infinity
     1.0f32 != f32::NEG_INFINITY; // and negative infinity
     ZERO == 0.0; //no error, comparison with zero is ok
     ZERO + ZERO != 1.0; //no error, comparison with zero is ok
 
+    let x = X { val: 1.0 };
+    x == 1.0; // no error, custom type that implement PartialOrder for float is not checked
+
     ONE == 1f32;
     ONE == 1.0 + 0.0;
     ONE + ONE == ZERO + ONE + ONE;

tests/ui/float_cmp.stderr

@@ -1,5 +1,5 @@
 error: strict comparison of `f32` or `f64`
-  --> $DIR/float_cmp.rs:57:5
+  --> $DIR/float_cmp.rs:70:5
    |
 LL |     ONE as f64 != 2.0;
    |     ^^^^^^^^^^^^^^^^^ help: consider comparing them within some margin of error: `(ONE as f64 - 2.0).abs() > error_margin`
@@ -8,39 +8,39 @@ LL |     ONE as f64 != 2.0;
    = note: `-D clippy::float-cmp` implied by `-D warnings`
 
 error: strict comparison of `f32` or `f64`
-  --> $DIR/float_cmp.rs:64:5
+  --> $DIR/float_cmp.rs:77:5
    |
 LL |     x == 1.0;
    |     ^^^^^^^^ help: consider comparing them within some margin of error: `(x - 1.0).abs() < error_margin`
    |
    = note: `f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`
 
 error: strict comparison of `f32` or `f64`
-  --> $DIR/float_cmp.rs:69:5
+  --> $DIR/float_cmp.rs:82:5
    |
 LL |     twice(x) != twice(ONE as f64);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider comparing them within some margin of error: `(twice(x) - twice(ONE as f64)).abs() > error_margin`
    |
    = note: `f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`
 
 error: strict comparison of `f32` or `f64`
-  --> $DIR/float_cmp.rs:91:5
+  --> $DIR/float_cmp.rs:104:5
    |
 LL |     NON_ZERO_ARRAY[i] == NON_ZERO_ARRAY[j];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider comparing them within some margin of error: `(NON_ZERO_ARRAY[i] - NON_ZERO_ARRAY[j]).abs() < error_margin`
    |
    = note: `f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`
 
 error: strict comparison of `f32` or `f64` arrays
-  --> $DIR/float_cmp.rs:98:5
+  --> $DIR/float_cmp.rs:111:5
    |
 LL |     a1 == a2;
    |     ^^^^^^^^
    |
    = note: `f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`
 
 error: strict comparison of `f32` or `f64`
-  --> $DIR/float_cmp.rs:101:5
+  --> $DIR/float_cmp.rs:114:5
    |
 LL |     a1[0] == a2[0];
    |     ^^^^^^^^^^^^^^ help: consider comparing them within some margin of error: `(a1[0] - a2[0]).abs() < error_margin`