Print the store paths to be fetched sorted by StorePath name() and no…

…t baseName

Presently when nix says something like:

```
these 486 paths will be fetched (511.54 MiB download, 6458.64 MiB unpacked):
 ...path1
 ...path2
 ...path3
    ...
    ...
 ...path486
```

It sorts path1, path2, path3, ..., path486 in lexicographic order of the
store path.

After this commit, nix will show path1, path2, path3, ..., path486 sorted by
StorePath name() (basically everything after the hash) rather than the store path.

This makes it easier to review what exactly is being downloaded at a glance,
especially when many paths need to be fetched.

src/libmain/shared.cc

@@ -84,7 +84,8 @@ void printMissing(ref<Store> store, const StorePathSet & willBuild,
  downloadSizeMiB,
  narSizeMiB);
  }
- for (auto & i : willSubstitute)
+ auto willSubstituteSorted = NameSortedStorePathSetView(willSubstitute.begin(), willSubstitute.end());
+ for (auto & i : willSubstituteSorted)
  printMsg(lvl, " %s", store->printStorePath(i));
  }
 

src/libstore/path.cc

@@ -81,7 +81,7 @@ StorePathSet Store::parseStorePathSet(const PathSet & paths) const
  return res;
 }
 
-std::string Store::printStorePath(const StorePath & path) const
+std::string Store::printStorePath(const StorePathView & path) const
 {
  return (storeDir + "/").append(path.to_string());
 }

src/libstore/path.hh

@@ -7,6 +7,7 @@
 namespace nix {
 
 struct Hash;
+class StorePathView;
 
 class StorePath
 {
@@ -64,7 +65,46 @@ public:
  static StorePath random(std::string_view name);
 };
 
+class StorePathView {
+ const StorePath *pStorePath;
+
+ public:
+ StorePathView() = delete;
+
+ StorePathView(const StorePath &spath) : pStorePath(&spath) {}
+
+ std::string_view to_string() const { return pStorePath->to_string(); }
+
+ bool isDerivation() const { return pStorePath->isDerivation(); }
+
+ std::string_view name() const { return pStorePath->name(); }
+
+ std::string_view hashPart() const { return pStorePath->hashPart(); }
+
+ bool operator<(const StorePathView &other) const {
+ return *pStorePath < *other.pStorePath;
+ }
+
+ bool operator==(const StorePathView &other) const {
+ return *pStorePath == *other.pStorePath;
+ }
+
+ bool operator!=(const StorePathView &other) const {
+ return *pStorePath != *other.pStorePath;
+ }
+};
+
+struct NameSortedLessForStorePathView {
+ bool operator()(const StorePathView &lhs, const StorePathView &rhs) const {
+ if (lhs.name() == rhs.name())
+ return lhs.to_string() < rhs.to_string();
+ else
+ return lhs.name() < rhs.name();
+ }
+};
+
 typedef std::set<StorePath> StorePathSet;
+typedef std::set<StorePathView, NameSortedLessForStorePathView> NameSortedStorePathSetView;
 typedef std::vector<StorePath> StorePaths;
 
 /* Extension of derivations in the Nix store. */

src/libstore/store-api.hh

@@ -173,7 +173,7 @@ public:
 
  std::optional<StorePath> maybeParseStorePath(std::string_view path) const;
 
- std::string printStorePath(const StorePath & path) const;
+ std::string printStorePath(const StorePathView & path) const;
 
  // FIXME: remove
  StorePathSet parseStorePathSet(const PathSet & paths) const;