net/netip: add test that Compare and reflect.DeepEqual match

Updates #68113

Change-Id: I1107686ef364f77f48f55534ea8ec68d1785e1e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/594375
Auto-Submit: Brad Fitzpatrick <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

src/net/netip/netip_test.go

@@ -893,6 +893,15 @@ func TestAddrLessCompare(t *testing.T) {
 		{mustIP("::1%a"), mustIP("::1%b"), true},
 		{mustIP("::1%a"), mustIP("::1%a"), false},
 		{mustIP("::1%b"), mustIP("::1%a"), false},
+
+		// For Issue 68113, verify that an IPv4 address and a
+		// v4-mapped-IPv6 address differing only in their zone
+		// pointer are unequal via all three of
+		// ==/Compare/reflect.DeepEqual. In Go 1.22 and
+		// earlier, these were accidentally equal via
+		// DeepEqual due to their zone pointers (z) differing
+		// but pointing to identical structures.
+		{mustIP("::ffff:11.1.1.12"), mustIP("11.1.1.12"), false},
 	}
 	for _, tt := range tests {
 		got := tt.a.Less(tt.b)
@@ -920,6 +929,12 @@ func TestAddrLessCompare(t *testing.T) {
 				t.Errorf("Less(%q, %q) was correctly %v, but so was Less(%q, %q)", tt.a, tt.b, got, tt.b, tt.a)
 			}
 		}
+
+		// Also check reflect.DeepEqual. See issue 68113.
+		deepEq := reflect.DeepEqual(tt.a, tt.b)
+		if (cmp == 0) != deepEq {
+			t.Errorf("%q and %q differ in == (%v) vs reflect.DeepEqual (%v)", tt.a, tt.b, cmp == 0, deepEq)
+		}
 	}
 
 	// And just sort.