Include the accessor in the SourcePath hash

src/libutil/source-path.hh

@@ -9,6 +9,8 @@
 #include "canon-path.hh"
 #include "source-accessor.hh"
 
+#include <boost/functional/hash.hpp> // for boost::hash_combine
+
 namespace nix {
 
 /**
@@ -128,6 +130,8 @@ struct std::hash<nix::SourcePath>
 {
     std::size_t operator()(const nix::SourcePath & s) const noexcept
     {
-        return std::hash<decltype(s.path)>{}(s.path);
+        std::size_t hash = 0;
+        hash_combine(hash, s.accessor->number, s.path);
+        return hash;
     }
 };

src/libutil/util.hh

@@ -360,4 +360,18 @@ inline std::string operator + (std::string_view s1, const char * s2)
     return s;
 }
 
+/**
+ * hash_combine() from Boost. Hash several hashable values together
+ * into a single hash.
+ */
+inline void hash_combine(std::size_t & seed) { }
+
+template <typename T, typename... Rest>
+inline void hash_combine(std::size_t & seed, const T & v, Rest... rest)
+{
+    std::hash<T> hasher;
+    seed ^= hasher(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
+    hash_combine(seed, rest...);
+}
+
 }