Generated dart code should import transitive imports.

mojo/public/tools/bindings/pylib/mojom/generate/generator.py

Index: mojo/public/tools/bindings/pylib/mojom/generate/generator.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
index 1d57528d3582852a19ce12238bfe5b283ed4a015..0e6258a875816ed72c33ef1410b438a2f0e700a6 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
@@ -5,6 +5,7 @@
 """Code shared by the various language-specific code generators."""
 
 from functools import partial
+from itertools import chain
 import os.path
 import re
 
@@ -62,6 +63,77 @@ class Generator(object):
   def GetInterfaces(self):
     return map(self._AddInterfaceComputedData, self.module.interfaces)
 
+  def GetUsedImports(self, module):
+    """GetUsedImports computes the imports that are used in the provided module.
+
+    An import being used means that a type or constant defined in the import is
+    referenced in the provided module.
+
+    Args:
+      module: {module.Module} The module whose used imports are to be computed.
+
+    Returns:
+      {dict<str, dict>} A dictionary of the used imports. The key is the file
+      name as defined in the import's Module.path. The value is a dictionary.
+      The contents of the dictionary is identical to that found in the
+      imported_from field of mojom elements.
+    """
+    used = {}
+
+    def AddImport(element):
+      """AddImport is a utility function that adds the import of the provided
+      element to the used dictionary defined above.
+      """
+      # Only named values or kinds could be imported.
+      if (not isinstance(element, mojom.Kind) and
+          not isinstance(element, mojom.NamedValue)):
+        return
+
+      if mojom.IsArrayKind(element) or mojom.IsInterfaceRequestKind(element):
+        AddImport(element.kind)
+        return
+      if mojom.IsMapKind(element):
+        AddImport(element.key_kind)
+        AddImport(element.value_kind)
+        return
+      if not hasattr(element, 'imported_from') or not element.imported_from:
+        return
+
+      imported_from = element.imported_from
+      used[imported_from['module'].path] = imported_from
+
+    # We want to collect the structs that represent method input and output
+    # parameters.
+    all_structs = list(module.structs)
+    for interface in module.interfaces:
+      for method in interface.methods:
+        all_structs.append(self._GetStructFromMethod(method))
+        if method.response_parameters:
+          all_structs.append(self._GetResponseStructFromMethod(method))
+
+    for struct in all_structs:
+      for field in struct.fields:
+        AddImport(field.kind)
+        if field.default:
+          AddImport(field.default)
+
+    # Enums can be defined in the module, in structs or in interfaces.
+    enum_containers = [module] + module.structs + module.interfaces
+    enums = [c.enums for c in enum_containers]
+    for enum in chain.from_iterable(enums):
+      for field in enum.fields:
+        if field.value:
+          AddImport(field.value)
+
+    for union in module.unions:
+      for field in union.fields:
+        AddImport(field.kind)
+
+    for constant in module.constants:
+      AddImport(constant.value)
+
+    return used
+
   # Prepend the filename with a directory that matches the directory of the
   # original .mojom file, relative to the import root.
   def MatchMojomFilePath(self, filename):