fix absurd extreme comparisons false positive

fixes #1387

clippy_lints/src/types.rs

@@ -825,6 +825,12 @@ fn detect_absurd_comparison<'a>(
     use types::AbsurdComparisonResult::*;
     use utils::comparisons::*;
 
+    // absurd comparison only makes sense on primitive types
+    // primitive types don't implement comparison operators with each other
+    if cx.tcx.tables().expr_ty(lhs) != cx.tcx.tables().expr_ty(rhs) {
+        return None;
+    }
+
     let normalized = normalize_comparison(op, lhs, rhs);
     let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
         val

tests/compile-fail/absurd-extreme-comparisons.rs

@@ -3,6 +3,7 @@
 
 #![deny(absurd_extreme_comparisons)]
 #![allow(unused, eq_op, no_effect, unnecessary_operation)]
+
 fn main() {
     const Z: u32 = 0;
 
@@ -70,3 +71,23 @@ fn main() {
     // this is handled by unit_cmp
     () < {}; //~WARNING <-comparison of unit values detected.
 }
+
+use std::cmp::{Ordering, PartialEq, PartialOrd};
+
+#[derive(PartialEq, PartialOrd)]
+pub struct U(u64);
+
+impl PartialEq<u32> for U {
+    fn eq(&self, other: &u32) -> bool {
+        self.eq(&U(*other as u64))
+    }
+}
+impl PartialOrd<u32> for U {
+    fn partial_cmp(&self, other: &u32) -> Option<Ordering> {
+        self.partial_cmp(&U(*other as u64))
+    }
+}
+
+pub fn foo(val: U) -> bool {
+    val > std::u32::MAX
+}