Improve unittest framework to have a virtual FS

This gets the unittest framework closer to the actual behavior,
and allows us to mock basic FS operations such as mkdir and writeFile.
Further improvements can be made to support more operations,
and to have package setup done before `TestDub` instantiation.

source/dub/packagemanager.d

@@ -9,7 +9,7 @@ module dub.packagemanager;
 
 import dub.dependency;
 import dub.internal.utils;
-import dub.internal.vibecompat.core.file;
+import dub.internal.vibecompat.core.file : FileInfo;
 import dub.internal.vibecompat.data.json;
 import dub.internal.vibecompat.inet.path;
 import dub.internal.logging;
@@ -760,6 +760,8 @@ class PackageManager {
 	Package store(NativePath src, PlacementLocation dest, in PackageName name,
 		in Version vers)
 	{
+		import dub.internal.vibecompat.core.file;
+
 		assert(!name.sub.length, "Cannot store a subpackage, use main package instead");
 		NativePath dstpath = this.getPackagePath(dest, name, vers.toString());
 		ensureDirectory(dstpath.parentPath());
@@ -779,6 +781,7 @@ class PackageManager {
 	private Package store_(NativePath src, NativePath destination,
 		in PackageName name, in Version vers)
 	{
+		import dub.internal.vibecompat.core.file;
 		import std.range : walkLength;
 
 		logDebug("Placing package '%s' version '%s' to location '%s' from file '%s'",
@@ -1033,6 +1036,8 @@ symlink_exit:
 	/// .svn folders)
 	Hash hashPackage(Package pack)
 	{
+		import dub.internal.vibecompat.core.file;
+
 		string[] ignored_directories = [".git", ".dub", ".svn"];
 		// something from .dub_ignore or what?
 		string[] ignored_files = [];
@@ -1088,6 +1093,23 @@ symlink_exit:
 			}
 		}
 	}
+
+	/// Used for dependency injection in `Location`
+	protected bool existsDirectory(NativePath path)
+	{
+		static import dub.internal.vibecompat.core.file;
+		return dub.internal.vibecompat.core.file.existsDirectory(path);
+	}
+
+	/// Ditto
+	protected alias IterateDirDg = int delegate(scope int delegate(ref FileInfo));
+
+	/// Ditto
+	protected IterateDirDg iterateDirectory(NativePath path)
+	{
+		static import dub.internal.vibecompat.core.file;
+		return dub.internal.vibecompat.core.file.iterateDirectory(path);
+	}
 }
 
 deprecated(OverrideDepMsg)
@@ -1229,6 +1251,8 @@ package struct Location {
 
 	void loadOverrides()
 	{
+		import dub.internal.vibecompat.core.file;
+
 		this.overrides = null;
 		auto ovrfilepath = this.packagePath ~ LocalOverridesFilename;
 		if (existsFile(ovrfilepath)) {
@@ -1248,6 +1272,8 @@ package struct Location {
 
 	private void writeOverrides()
 	{
+		import dub.internal.vibecompat.core.file;
+
 		Json[] newlist;
 		foreach (ovr; this.overrides) {
 			auto jovr = Json.emptyObject;
@@ -1266,6 +1292,8 @@ package struct Location {
 
 	private void writeLocalPackageList()
 	{
+		import dub.internal.vibecompat.core.file;
+
 		Json[] newlist;
 		foreach (p; this.searchPath) {
 			auto entry = Json.emptyObject;
@@ -1291,6 +1319,8 @@ package struct Location {
 	// load locally defined packages
 	void scanLocalPackages(bool refresh, PackageManager manager)
 	{
+		import dub.internal.vibecompat.core.file;
+
 		NativePath list_path = this.packagePath;
 		Package[] packs;
 		NativePath[] paths;
@@ -1372,7 +1402,7 @@ package struct Location {
 	void scanPackageFolder(NativePath path, PackageManager mgr,
 		Package[] existing_packages)
 	{
-		if (!path.existsDirectory())
+		if (!mgr.existsDirectory(path))
 			return;
 
 		void loadInternal (NativePath pack_path, NativePath packageFile)
@@ -1396,7 +1426,7 @@ package struct Location {
 		}
 
 		logDebug("iterating dir %s", path.toNativeString());
-		try foreach (pdir; iterateDirectory(path)) {
+		try foreach (pdir; mgr.iterateDirectory(path)) {
 			logDebug("iterating dir %s entry %s", path.toNativeString(), pdir.name);
 			if (!pdir.isDirectory) continue;
 
@@ -1417,10 +1447,10 @@ package struct Location {
 			// This is the most common code path
 			else if (mgr.isManagedPath(path)) {
 				// Iterate over versions of a package
-				foreach (versdir; iterateDirectory(pack_path)) {
+				foreach (versdir; mgr.iterateDirectory(pack_path)) {
 					if (!versdir.isDirectory) continue;
 					auto vers_path = pack_path ~ versdir.name ~ (pdir.name ~ "/");
-					if (!vers_path.existsDirectory()) continue;
+					if (!mgr.existsDirectory(vers_path)) continue;
 					packageFile = Package.findPackageFile(vers_path);
 					loadInternal(vers_path, packageFile);
 				}
@@ -1480,7 +1510,7 @@ package struct Location {
 
 		string versStr = vers.toString();
 		const path = this.getPackagePath(name, versStr);
-		if (!path.existsDirectory())
+		if (!mgr.existsDirectory(path))
 			return null;
 
 		logDiagnostic("Lazily loading package %s:%s from %s", name.main, vers, path);