Put in some frosting.

build.py

@@ -569,6 +569,8 @@ class CustomTarget:
         self.subdir = subdir
         self.dependencies = []
         self.process_kwargs(kwargs)
+        self.sources = []
+        self.extra_files = []
 
     def process_kwargs(self, kwargs):
         if 'output' not in kwargs:
@@ -632,6 +634,12 @@ class CustomTarget:
     def get_aliaslist(self):
         return []
 
+    def get_sources(self):
+        return self.sources
+
+    def get_generated_sources(self):
+        return []
+
 class Jar(BuildTarget):
     def __init__(self, name, subdir, is_cross, sources, objects, environment, kwargs):
         super().__init__(name, subdir, is_cross, sources, objects, environment, kwargs);

mesongui.py

@@ -94,6 +94,8 @@ class TargetModel(QAbstractItemModel):
                 typename = 'shared library'
             elif isinstance(target, build.StaticLibrary):
                 typename = 'static library'
+            elif isinstance(target, build.CustomTarget):
+                typename = 'custom'
             else:
                 typename = 'unknown'
             if target.should_install():

mesonintrospect.py

@@ -50,6 +50,8 @@ def list_targets(coredata, builddata):
             typename = 'shared library'
         elif isinstance(target, build.StaticLibrary):
             typename = 'static library'
+        elif isinstance(target, build.CustomTarget):
+            typename = 'custom'
         else:
             typename = 'unknown'
         t['type'] = typename