Allow Glean to be substituted for local development

settings.gradle

@@ -48,6 +48,7 @@ gradle.projectsLoaded { ->
 
 Properties localProperties = null;
 String settingAppServicesPath = "substitutions.application-services.dir";
+String settingGleanPath = "substitutions.glean.dir";
 
 if (file('local.properties').canRead()) {
     localProperties = new Properties()
@@ -71,4 +72,19 @@ if (localProperties != null) {
     } else {
         logger.lifecycle("Local configuration: application-services substitution path missing. You may specify it via '$settingAppServicesPath' setting.")
     }
+
+    String gleanLocalPath = localProperties.getProperty(settingGleanPath);
+
+    if (gleanLocalPath != null) {
+        logger.lifecycle("Local configuration: substituting glean module from path: $gleanLocalPath")
+
+        includeBuild(gleanLocalPath) {
+            dependencySubstitution {
+                substitute module('org.mozilla.telemetry:glean') with project(':glean')
+                    substitute module('org.mozilla.telemetry:glean-forUnitTests') with project(':glean')
+            }
+        }
+    } else {
+        logger.lifecycle("Local configuration: glean substitution path missing. You may specify it via '$settingGleanPath' setting.")
+    }
 }