-B, --print-deps option added.

src/main.cr

@@ -19,6 +19,7 @@ download_only = false
 do_not_clean = false
 watch_only = false
 skip_build_dependencies = false
+print_deps = false
 
 used_X = false
 OptionParser.parse! do |parser|
@@ -61,6 +62,10 @@ OptionParser.parse! do |parser|
 		watch_only = true
 	}
 
+	parser.on("-B", "--print-deps", "Prints build dependencies and exits.") {
+		print_deps = true
+	}
+
 	parser.on("-v", "--verbose", "Runs more verbosely.") {
 		context.verbosity += 1
 	}
@@ -137,6 +142,11 @@ begin
 		end
 	end
 
+	if print_deps
+		puts dependencies.join "\n"
+		exit 0
+	end
+
 	if dependencies.size > 0 && ! skip_build_dependencies && !download_only
 		# FIXME: We’ll probably want to have backends other than apk at some point.
 		opts = ["add"] + (ENV["APK_FLAGS"]? || "-i").split(/[ \t]+/) + dependencies