WIP: automatically migrate client-side profiles back to /nix/var/nix

Change-Id: I430dbfabfa091417f0883975a0c1611ab62655d1

src/libstore/profiles.cc

@@ -336,6 +336,18 @@ Path ensureDefaultProfile()
         replaceSymlink(defaultProfile, profileLink);
     }
 
+    Path const profileLinkTarget = readLink(profileLink);
+    std::cerr << "profileLinkTarget: " << profileLinkTarget << "\n";
+    // Note: getStateDir() is XDG_STATE_DIR, not NIX_STATE_DIR.
+    if (profileLinkTarget.starts_with(createNixStateDir())) {
+        notice("migrating client-side profiles to %s", profilesDir());
+        Path const cspDir = createNixStateDir() + "/profiles";
+        Path const dspDir = profilesDir();
+        migrateProfiles(cspDir, dspDir);
+        std::cerr << fmt("replaceSymlink(%s, %s)\n", defaultProfile, profileLink);
+        replaceSymlink(defaultProfile, profileLink);
+    }
+
     // Backwards compatibiliy measure: Make root's profile available as
     // `.../default` as it's what NixOS and most of the init scripts expect
     Path const globalProfileLink = settings.nixStateDir + "/profiles/default";
@@ -343,7 +355,7 @@ Path ensureDefaultProfile()
         replaceSymlink(defaultProfile, globalProfileLink);
     }
 
-    return absPath(readLink(profileLink), dirOf(profileLink));
+    return absPath(profileLinkTarget, dirOf(profileLink));
 }
 
 Path getDefaultProfile()
@@ -363,6 +375,51 @@ Path getDefaultProfile()
     return profileLink;
 }
 
+void migrateProfiles(Path const & profilesFrom, Path const & profilesTo)
+{
+    notice("migrating from profiles from %s to be in %s", profilesFrom, profilesTo);
+    auto const oldProfiles = readDirectory(profilesFrom);
+
+    for (DirEntry const & oldProfileEnt : oldProfiles) {
+        auto const oldGenPath = fmt("%s/%s", profilesFrom, oldProfileEnt.name);
+        if (!isLink(oldGenPath)) {
+            // This is not a profile and we should not touch it.
+            continue;
+        }
+
+        auto const newGenPath = fmt("%s/%s", profilesTo, oldProfileEnt.name);
+        auto const genTarget = readLink(oldGenPath);
+        notice("migrating profile '%s' to '%s'", oldGenPath, newGenPath);
+        std::cerr << fmt("replaceSymlink(%s, %s)", genTarget, newGenPath);
+        //replaceSymlink(genTarget, newGenPath);
+
+        //deletePath(oldGenPath);
+    }
+
+    // Now that we've deleted all the profile symlinks in ~/.local/state/nix/profiles,
+    // it's time to make ~/.local/state/nix/profiles itself a symlink.
+    if (readDirectory(profilesFrom).empty()) {
+        removeFile(profilesFrom);
+        replaceSymlink(profilesTo, profilesFrom);
+    } else {
+        // But if that directory stuff other than profiles in it, we shouldn't delete that.
+        // Back them up for the user.
+        warn("non-profiles found in '%s'; backing up instead of deleting", profilesFrom);
+        Path backupName = profilesFrom + ".bak";
+        if (pathExists(backupName)) {
+            unsigned suffix = 0;
+            do {
+                assert(suffix < UINT_MAX);
+                suffix += 1;
+                backupName = fmt("%s.bak-%u", profilesFrom, suffix);
+            } while (pathExists(backupName));
+        }
+
+        renameFile(profilesFrom, backupName);
+        notice("backed up as '%s'", backupName);
+    }
+}
+
 Path defaultChannelsDir()
 {
     return profilesDir() + "/channels";

src/libstore/profiles.hh

@@ -245,4 +245,12 @@ Path getDefaultProfile();
  */
 Path ensureDefaultProfile();
 
+/**
+ * Migrates a set of profiles from one directory to another.
+ *
+ * Intended for migration from ~/.local/state/nix/profiles/
+ * to /nix/var/nix/profiles/per-user/foo/
+ */
+void migrateProfiles(Path const & profilesFrom, Path const & profilesTo);
+
 }