Devtools: refactor shell configuration logic.

mojo/devtools/common/devtoolslib/paths.py

Index: mojo/devtools/common/devtoolslib/paths.py
diff --git a/mojo/devtools/common/devtoolslib/paths.py b/mojo/devtools/common/devtoolslib/paths.py
index 3347c754fd86a8f78da3ba75b1b053ca6fb6f069..1b0bff4720377f99d12cccff02a14a385d13f090 100644
--- a/mojo/devtools/common/devtoolslib/paths.py
+++ b/mojo/devtools/common/devtoolslib/paths.py
@@ -8,6 +8,7 @@ These functions allow devtools scripts to work out-of-the-box with regular Mojo
 checkouts.
 """
 
+import collections
 import os.path
 import sys
 
@@ -26,13 +27,13 @@ def find_ancestor_with(relpath):
       return None
 
 
-def infer_mojo_paths(is_android, is_debug, target_cpu):
-  """Infers the locations of select build output artifacts in a regular Mojo
-  checkout.
+def infer_paths(is_android, is_debug, target_cpu):
+  """Infers the locations of select build output artifacts in a regular
+  Chromium-like checkout. This should grow thinner or disappear as we introduce
+  per-repo config files, see https://github.com/domokit/devtools/issues/28.
 
   Returns:
-    Tuple of path dictionary, error message. Only one of the two will be
-    not-None.
+    Defaultdict with the inferred paths.
   """
   build_dir = (('android_' if is_android else '') +
                (target_cpu + '_' if target_cpu else '') +
@@ -40,20 +41,19 @@ def infer_mojo_paths(is_android, is_debug, target_cpu):
   out_build_dir = os.path.join('out', build_dir)
 
   root_path = find_ancestor_with(out_build_dir)
+  paths = collections.defaultdict(lambda: None)
   if not root_path:
-    return None, ('Failed to find build directory: ' + out_build_dir)
+    return paths
 
-  paths = {}
-  paths['root'] = root_path
   build_dir_path = os.path.join(root_path, out_build_dir)
-  paths['build'] = build_dir_path
+  paths['build_dir_path'] = build_dir_path
   if is_android:
-    paths['shell'] = os.path.join(build_dir_path, 'apks', 'MojoShell.apk')
-    paths['adb'] = os.path.join(root_path, 'third_party', 'android_tools',
+    paths['shell_path'] = os.path.join(build_dir_path, 'apks', 'MojoShell.apk')
+    paths['adb_path'] = os.path.join(root_path, 'third_party', 'android_tools',
                                 'sdk', 'platform-tools', 'adb')
   else:
-    paths['shell'] = os.path.join(build_dir_path, 'mojo_shell')
-  return paths, None
+    paths['shell_path'] = os.path.join(build_dir_path, 'mojo_shell')
+  return paths
 
 
 # Based on Chromium //tools/find_depot_tools.py.