app: Centralize directory validation

This allows us to avoid duplication of code and ensure validation
happens regardless of who's initializing the class. We introduce a new
exception - ApplicationError - to indicate these kinds of issues. This
subclasses SphinxError, meaning we don't need to modify our exception
handling code.

Signed-off-by: Stephen Finucane <stephen@that.guru>

1 files changed, 5 insertions, 0 deletions

diff --git a/sphinx/errors.py b/sphinx/errors.py
index eef1a157a..10cdfbb2d 100644
--- a/sphinx/errors.py
+++ b/sphinx/errors.py
@@ -28,6 +28,11 @@ class SphinxWarning(SphinxError):
     category = 'Warning, treated as error'
 
 
+class ApplicationError(SphinxError):
+    """Application initialization error."""
+    category = 'Application error'
+
+
 class ExtensionError(SphinxError):
     """Raised if something's wrong with the configuration."""
     category = 'Extension error'