add --deep flag to dub build

Allows to build all dependencies of a static library

source/dub/commandline.d

@@ -1198,6 +1198,7 @@ class GenerateCommand : PackageBuildCommand {
 	protected {
 		string m_generator;
 		bool m_printPlatform, m_printBuilds, m_printConfigs;
+		bool m_deep; // only set in BuildCommand
 	}
 
 	this() @safe pure nothrow
@@ -1274,6 +1275,7 @@ class GenerateCommand : PackageBuildCommand {
 		gensettings.runArgs = app_args;
 		// legacy compatibility, default working directory is always CWD
 		gensettings.overrideToolWorkingDirectory = getWorkingDirectory();
+		gensettings.buildDeep = m_deep;
 
 		logDiagnostic("Generating using %s", m_generator);
 		dub.generateProject(m_generator, gensettings);
@@ -1316,6 +1318,9 @@ class BuildCommand : GenerateCommand {
 		args.getopt("n|non-interactive", &m_nonInteractive, [
 			"Don't enter interactive mode."
 		]);
+		args.getopt("d|deep", &m_deep, [
+			"Build all dependencies, even when main target is a static library."
+		]);
 		super.prepare(args);
 		m_generator = "build";
 	}

source/dub/generators/build.d

@@ -159,9 +159,9 @@ class BuildGenerator : ProjectGenerator {
 		}
 
 		// build all targets
-		if (settings.rdmd || rootTT == TargetType.staticLibrary) {
+		if (settings.rdmd || (rootTT == TargetType.staticLibrary && !settings.buildDeep)) {
 			// RDMD always builds everything at once and static libraries don't need their
-			// dependencies to be built
+			// dependencies to be built, unless --deep flag is specified
 			NativePath tpath;
 			buildTarget(settings, root_ti.buildSettings.dup, m_project.rootPackage, root_ti.config, root_ti.packages, null, tpath);
 			return;

source/dub/generators/generator.d

@@ -824,6 +824,9 @@ struct GeneratorSettings {
 	/// single file dub package
 	bool single;
 
+	/// build all dependencies for static libraries
+	bool buildDeep;
+
 	string[] runArgs;
 	void delegate(int status, string output) compileCallback;
 	void delegate(int status, string output) linkCallback;