Dub: Deprecate changing the rootPath

It's an essential part of the setup, and too many properties are derived
from it that we don't want to let the library user the ability to mess with it.

Author: Geod24

source/dub/commandline.d

@@ -758,8 +758,7 @@ class Command {
 		Dub dub;
 
 		if (options.bare) {
-			dub = new Dub(NativePath(getcwd()));
-			dub.rootPath = NativePath(options.root_path);
+			dub = new Dub(NativePath(options.root_path), NativePath(getcwd()));
 			dub.defaultPlacementLocation = options.placementLocation;
 
 			return dub;
@@ -2379,7 +2378,7 @@ class DustmiteCommand : PackageBuildCommand {
 	{
 		if (!m_testPackage.length)
 			return super.prepareDub(options);
-		return new Dub(NativePath(getcwd()));
+		return new Dub(NativePath(options.root_path), NativePath(getcwd()));
 	}
 
 	override int execute(Dub dub, string[] free_args, string[] app_args)

source/dub/dub.d

@@ -183,12 +183,27 @@ class Dub {
 		loading a package.
 
 		This constructor corresponds to the "--bare" option of the command line
-		interface. Use
+		interface.
+
+		Params:
+		  root = The root path of the Dub instance itself.
+		  pkg_root = The root of the location where packages are located
+					 Only packages under this location will be accessible.
+					 Note that packages at the top levels will be ignored.
 	*/
-	this(NativePath override_path)
+	this(NativePath root, NativePath pkg_root)
 	{
+		// Note: We're doing `init()` before setting the `rootPath`,
+		// to prevent `init` from reading the project's settings.
 		init();
-		m_packageManager = new PackageManager(override_path);
+		this.m_rootPath = root;
+		m_packageManager = new PackageManager(pkg_root);
+	}
+
+	deprecated("Use the overload that takes `(NativePath pkg_root, NativePath root)`")
+	this(NativePath pkg_root)
+	{
+		this(pkg_root, pkg_root);
 	}
 
 	private void init()
@@ -361,6 +376,8 @@ class Dub {
 	*/
 	@property NativePath rootPath() const { return m_rootPath; }
 	/// ditto
+	deprecated("Changing the root path is deprecated as it has non-obvious pitfalls " ~
+			   "(e.g. settings aren't reloaded). Instantiate a new `Dub` instead")
 	@property void rootPath(NativePath root_path)
 	{
 		m_rootPath = root_path;