Fixed problem with plugin precedence

We were unpacking plugin tiddlers in arbitrary order, and ensuring that
later plugins didn't overwrite shadow tiddlers from earlier plugins.

Now we'll allow plugins to specify a "pluginPriority" that determines
the load ordering. We also explicitly allow shadow tiddlers from later
plugins to overwrite shadow tiddlers from earlier plugins.

We're setting a base priority on the core plugin, since many plugins
will want to control their loading relative to it.

boot/boot.js

@@ -547,25 +547,43 @@ $tw.Wiki.prototype.addTiddlers = function(tiddlers) {
 Extract constituent tiddlers from plugin tiddlers so that we can easily access them in getTiddler()
 */
 $tw.Wiki.prototype.unpackPluginTiddlers = function() {
-	// Collect up all the plugin tiddlers
-	var self = this;
+	// Collect up the titles of all the plugin tiddlers
+	var self = this,
+		pluginInfoList = [];
 	$tw.utils.each(this.tiddlers,function(tiddler,title,object) {
 		if(tiddler.fields.type === "application/json" && tiddler.hasField("plugin")) {
-			// Save the plugin information
-			var pluginInfo = self.plugins[title] = JSON.parse(tiddler.fields.text);
-			// Extract the constituent tiddlers
-			$tw.utils.each(pluginInfo.tiddlers,function(constituentTiddler,constituentTitle) {
-				// Don't overwrite tiddlers that already exist
-				if(!$tw.utils.hop(self.shadowTiddlers,constituentTitle)) {
-					// Save the tiddler object
-					self.shadowTiddlers[constituentTitle] = {
-						source: title,
-						tiddler: new $tw.Tiddler(constituentTiddler,{title: constituentTitle})
-					};
-				}
-			});
+			pluginInfoList.push(tiddler);
 		}
 	});
+	// Sort the titles by the `pluginPriority` field
+	pluginInfoList.sort(function(a,b) {
+		if("pluginPriority" in a.fields && "pluginPriority" in b.fields) {
+			return a.fields.pluginPriority - b.fields.pluginPriority;
+		} else if("pluginPriority" in a.fields) {
+			return -1;
+		} else if("pluginPriority" in b.fields) {
+			return +1;
+		} else if(a.fields.title < b.fields.title) {
+			return -1;
+		} else if(a.fields.title === b.fields.title) {
+			return 0;
+		} else {
+			return +1;
+		}
+	});
+	// Now go through the plugins in ascending order
+	$tw.utils.each(pluginInfoList,function(tiddler) {
+		// Save the plugin information
+		var pluginInfo = self.plugins[tiddler.fields.title] = JSON.parse(tiddler.fields.text);
+		// Extract the constituent tiddlers
+		$tw.utils.each(pluginInfo.tiddlers,function(constituentTiddler,constituentTitle) {
+			// Save the tiddler object
+			self.shadowTiddlers[constituentTitle] = {
+				source: tiddler.fields.title,
+				tiddler: new $tw.Tiddler(constituentTiddler,{title: constituentTitle})
+			};
+		});
+	});
 };
 
 /*
@@ -993,12 +1011,20 @@ $tw.loadPluginFolder = function(filepath,excludeRegExp) {
 		}
 	}
 	// Save the plugin tiddler
-	return pluginInfo ? {
-		title: pluginInfo.title,
-		type: "application/json",
-		plugin: "yes",
-		text: JSON.stringify(pluginInfo,null,4)
-	} : null;
+	if(pluginInfo) {
+		var fields = {
+			title: pluginInfo.title,
+			type: "application/json",
+			plugin: "yes",
+			text: JSON.stringify(pluginInfo,null,4)
+		}
+		if("pluginPriority" in pluginInfo) {
+			fields.pluginPriority = pluginInfo.pluginPriority;
+		}
+		return fields;
+	} else {
+		return null;
+	}
 };
 
 /*

core/plugin.info

@@ -3,5 +3,6 @@
 	"description": "TiddlyWiki5 core plugin",
 	"author": "JeremyRuston",
 	"version": "0.0.0",
-	"coreVersion": ">=5.0.0"
+	"coreVersion": ">=5.0.0",
+	"pluginPriority": "0"
 }