Merge pull request #8735 from obsidiansystems/defexpr

Factor out `nix-defexpr` path computation

src/libexpr/eval-settings.cc

@@ -63,7 +63,7 @@ Strings EvalSettings::getDefaultNixPath()
     };
 
     if (!evalSettings.restrictEval && !evalSettings.pureEval) {
-        add(settings.useXDGBaseDirectories ? getStateDir() + "/nix/defexpr/channels" : getHome() + "/.nix-defexpr/channels");
+        add(getNixDefExpr() + "/channels");
         add(rootChannelsDir() + "/nixpkgs", "nixpkgs");
         add(rootChannelsDir());
     }
@@ -92,4 +92,11 @@ EvalSettings evalSettings;
 
 static GlobalConfig::Register rEvalSettings(&evalSettings);
 
+Path getNixDefExpr()
+{
+    return settings.useXDGBaseDirectories
+        ? getStateDir() + "/nix/defexpr"
+        : getHome() + "/.nix-defexpr";
+}
+
 }

src/libexpr/eval-settings.hh

@@ -95,4 +95,9 @@ struct EvalSettings : Config
 
 extern EvalSettings evalSettings;
 
+/**
+ * Conventionally part of the default nix path in impure mode.
+ */
+Path getNixDefExpr();
+
 }