Fix #2706: Dub run ignores locally registered packages

The code was overly complicated and failed to do what it intended.
If a version was provided, it would always call 'fetch' even though
getBestPackage would have returned something.
Assuming that sub-packages are always present is also not working,
as the following would fail:
$ rm -rf ~/.dub/packages/vibe-d && dub run vibe-d:data
    Warning Package 'vibe-d:data' was neither found locally nor online.
The new code is both shorter and simpler, taking advantage
of the various improvements made to the APIs over the year
(for example, getBestPackage with VersionRange.Any does the right thing).

source/dub/commandline.d

@@ -1537,7 +1537,6 @@ class BuildCommand : GenerateCommand {
 
 	private int fetchMissingPackages(Dub dub, in UserPackageDesc packageParts)
 	{
-
 		static bool input(string caption, bool default_value = true) {
 			writef("%s [%s]: ", caption, default_value ? "Y/n" : "y/N");
 			auto inp = readln();
@@ -1554,42 +1553,41 @@ class BuildCommand : GenerateCommand {
 			}
 		}
 
-		VersionRange dep;
-
-		if (packageParts.range != VersionRange.Any) {
-			// the user provided a version manually
-			dep = packageParts.range;
-		} else if (packageParts.name.startsWith(":")) {
-			// Sub-packages are always assumed to be present
-			return 0;
-		} else if (dub.packageManager.getBestPackage(packageParts.name)) {
-			// found locally
+		// Local subpackages are always assumed to be present
+		if (packageParts.name.startsWith(":"))
 			return 0;
-		} else {
-			// search for the package and filter versions for exact matches
-			auto basePackageName = getBasePackageName(packageParts.name);
-			auto search = dub.searchPackages(basePackageName)
-				.map!(tup => tup[1].find!(p => p.name == basePackageName))
-				.filter!(ps => !ps.empty);
-			if (search.empty) {
-				logWarn("Package '%s' was neither found locally nor online.", packageParts.name);
-				return 2;
-			}
 
-			const p = search.front.front;
-			logInfo("Package '%s' was not found locally but is available online:", packageParts.name);
-			logInfo("---");
-			logInfo("Description: %s", p.description);
-			logInfo("Version: %s", p.version_);
-			logInfo("---");
+		const baseName = getBasePackageName(packageParts.name);
+		// Found locally
+		if (dub.packageManager.getBestPackage(baseName, packageParts.range))
+			return 0;
 
-			const answer = m_yes ? true : input("Do you want to fetch '%s' now?".format(packageParts.name));
-			if (!answer)
-				return 0;
-			dep = VersionRange.fromString(p.version_);
+		// Non-interactive, either via flag, or because a version was provided
+		if (m_yes || !packageParts.range.matchesAny()) {
+			dub.fetch(baseName, packageParts.range, dub.defaultPlacementLocation,
+				FetchOptions.none);
+			return 0;
 		}
+		// Otherwise we go the long way of asking the user.
+		// search for the package and filter versions for exact matches
+		auto search = dub.searchPackages(baseName)
+			.map!(tup => tup[1].find!(p => p.name == baseName))
+			.filter!(ps => !ps.empty);
+		if (search.empty) {
+			logWarn("Package '%s' was neither found locally nor online.", packageParts);
+			return 2;
+		}
+
+		const p = search.front.front;
+		logInfo("Package '%s' was not found locally but is available online:", packageParts);
+		logInfo("---");
+		logInfo("Description: %s", p.description);
+		logInfo("Version: %s", p.version_);
+		logInfo("---");
 
-		dub.fetch(packageParts.name, dep, dub.defaultPlacementLocation, FetchOptions.none);
+		if (input("Do you want to fetch '%s@%s' now?".format(packageParts, p.version_)))
+			dub.fetch(baseName, VersionRange.fromString(p.version_),
+				dub.defaultPlacementLocation, FetchOptions.none);
 		return 0;
 	}
 }