1 files changed, 86 insertions, 0 deletions
diff --git a/test/cmp6.go b/test/cmp6.go
new file mode 100644
index 0000000..704ead2
--- /dev/null
+++ b/test/cmp6.go
@@ -0,0 +1,86 @@
+// errorcheck
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Verify that incorrect comparisons are detected.
+// Does not compile.
+
+package main
+
+func use(bool) {}
+
+type T1 *int
+type T2 *int
+
+type T3 struct{ z []int }
+
+var t3 T3
+
+type T4 struct {
+	_ []int
+	a float64
+}
+
+var t4 T4
+
+func main() {
+	// Arguments to comparison must be
+	// assignable one to the other (or vice versa)
+	// so chan int can be compared against
+	// directional channels but channel of different
+	// direction cannot be compared against each other.
+	var c1 chan<- int
+	var c2 <-chan int
+	var c3 chan int
+
+	use(c1 == c2) // ERROR "invalid operation|incompatible"
+	use(c2 == c1) // ERROR "invalid operation|incompatible"
+	use(c1 == c3)
+	use(c2 == c2)
+	use(c3 == c1)
+	use(c3 == c2)
+
+	// Same applies to named types.
+	var p1 T1
+	var p2 T2
+	var p3 *int
+
+	use(p1 == p2) // ERROR "invalid operation|incompatible"
+	use(p2 == p1) // ERROR "invalid operation|incompatible"
+	use(p1 == p3)
+	use(p2 == p2)
+	use(p3 == p1)
+	use(p3 == p2)
+
+	// Arrays are comparable if and only if their element type is comparable.
+	var a1 [1]int
+	var a2 [1]func()
+	var a3 [0]func()
+	use(a1 == a1)
+	use(a2 == a2) // ERROR "invalid operation|invalid comparison"
+	use(a3 == a3) // ERROR "invalid operation|invalid comparison"
+
+	// Comparison of structs should have a good message
+	use(t3 == t3) // ERROR "struct|expected|cannot compare"
+	use(t4 == t4) // ERROR "cannot be compared|non-comparable|cannot compare"
+
+	// Slices, functions, and maps too.
+	var x []int
+	var f func()
+	var m map[int]int
+	use(x == x) // ERROR "slice can only be compared to nil|cannot compare"
+	use(f == f) // ERROR "func can only be compared to nil|cannot compare"
+	use(m == m) // ERROR "map can only be compared to nil|cannot compare"
+
+	// Comparison with interface that cannot return true
+	// (would panic).
+	var i interface{}
+	use(i == x) // ERROR "invalid operation"
+	use(x == i) // ERROR "invalid operation"
+	use(i == f) // ERROR "invalid operation"
+	use(f == i) // ERROR "invalid operation"
+	use(i == m) // ERROR "invalid operation"
+	use(m == i) // ERROR "invalid operation"
+}