Extractor: fall back to full extraction on overlay changes json read error

Author: d10c

python/extractor/semmle/traverser.py

@@ -34,10 +34,16 @@ def __init__(self, options, modulenames, logger):
         # During overlay extraction, only traverse the files that were changed.
         self.overlay_changes = None
         if 'CODEQL_EXTRACTOR_PYTHON_OVERLAY_CHANGES' in os.environ:
-            with open(os.environ['CODEQL_EXTRACTOR_PYTHON_OVERLAY_CHANGES'], 'r', encoding='utf-8') as f:
-                data = json.load(f)
-                changed_paths = data.get('changes', [])
-                self.overlay_changes = { os.path.abspath(p) for p in changed_paths }
+            overlay_changes_file = os.environ['CODEQL_EXTRACTOR_PYTHON_OVERLAY_CHANGES']
+            logger.info("Overlay extraction mode: only extracting files changed according to '%s'", overlay_changes_file)
+            try:
+                with open(overlay_changes_file, 'r', encoding='utf-8') as f:
+                    data = json.load(f)
+                    changed_paths = data.get('changes', [])
+                    self.overlay_changes = { os.path.abspath(p) for p in changed_paths }
+            except (IOError, ValueError) as e:
+                logger.warn("Failed to read overlay changes from '%s' (falling back to full extraction): %s", overlay_changes_file, e)
+                self.overlay_changes = None
         self.exclude_paths = set([ os.path.abspath(f) for f in options.exclude_file ])
         self.exclude = exclude_filter_from_options(options)
         self.filter = filter_from_options_and_environment(options)