Rust: Make crate fallback logic more conservative in path resolution library

Author: hvitved

rust/ql/lib/codeql/rust/internal/PathResolution.qll

@@ -1529,11 +1529,11 @@ private predicate crateDependencyEdge(SourceFileItemNode file, string name, Crat
   crateDependency(file, name, dep)
   or
   // As a fallback, give all files access to crates that do not conflict with known dependencies
-  // and declarations. This is in order to workaround incomplete crate dependency information
-  // provided by the extractor, as well as `CrateItemNode.getASourceFile()` being unable to map
-  // a given file to its crate (for example, if the file is `mod` imported inside a macro that the
-  // extractor is unable to expand).
-  name = dep.getName() and
+  // and declarations, as long as those crates have a unique name.
+  // This is in order to workaround incomplete crate dependency information provided by the extractor,
+  // as well as `CrateItemNode.getASourceFile()` being unable to map a given file to its crate (for
+  // example, if the file is `mod` imported inside a macro that the extractor is unable to expand).
+  dep = unique(CrateItemNode dep0 | name = dep0.getName()) and
   not hasDeclOrDep(file, name)
 }
 
@@ -2385,6 +2385,11 @@ private module Debug {
     useImportEdge(use, name, item, kind)
   }
 
+  predicate debugCrateDependencyEdge(SourceFileItemNode file, string name, CrateItemNode dep) {
+    file = getRelevantLocatable() and
+    crateDependencyEdge(file, name, dep)
+  }
+
   ItemNode debugGetASuccessor(ItemNode i, string name, SuccessorKind kind) {
     i = getRelevantLocatable() and
     result = i.getASuccessor(name, kind, _)