add pub-piv prop tests.

This was supposed to be in rust-lang#6653, but was lost in the edits of history.
Reconstructed from 5522aba

tests/testsuite/support/resolver.rs

@@ -1,6 +1,6 @@
 use std::cmp::PartialEq;
 use std::cmp::{max, min};
-use std::collections::{BTreeMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::fmt;
 use std::time::Instant;
 
@@ -54,6 +54,34 @@ pub fn resolve_and_validated(
     }
     let out = resolve.sort();
     assert_eq!(out.len(), used.len());
+
+    let mut pub_deps: HashMap<PackageId, HashSet<_>> = HashMap::new();
+    for &p in out.iter() {
+        // make the list of `p` public dependencies
+        let mut self_pub_dep = HashSet::new();
+        self_pub_dep.insert(p);
+        for (dp, deps) in resolve.deps(p) {
+            if deps.iter().any(|d| d.is_public()) {
+                self_pub_dep.extend(pub_deps[&dp].iter().cloned())
+            }
+        }
+        pub_deps.insert(p, self_pub_dep);
+
+        // check if `p` has a public dependencies conflicts
+        let seen_dep: BTreeSet<_> = resolve
+            .deps(p)
+            .flat_map(|(dp, _)| pub_deps[&dp].iter().cloned())
+            .collect();
+        let seen_dep: Vec<_> = seen_dep.iter().collect();
+        for a in seen_dep.windows(2) {
+            if a[0].name() == a[1].name() {
+                panic!(
+                    "the package {:?} can publicly see {:?} and {:?}",
+                    p, a[0], a[1]
+                )
+            }
+        }
+    }
     Ok(out)
 }