Load YAML configuration file with aliases: true

Gracefully handle breaking behavior in upstream Psych gem to support
YAML aliases.

Author: sds

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Overcommit Changelog
 
+## master (unreleased)
+
+* Gracefully handle breaking behavior in upstream Psych gem to support YAML aliases.
+
 ## 0.57.0
 
 * Fix `CommitMsg` hooks to be able to call `modified_lines_in_file`.

lib/overcommit/configuration_loader.rb

@@ -24,13 +24,16 @@ def default_configuration
       # @option logger [Overcommit::Logger]
       # @return [Overcommit::Configuration]
       def load_from_file(file, options = {})
-        hash =
-          if yaml = YAML.load_file(file)
-            yaml.to_hash
-          else
-            {}
+        # Psych 4 introduced breaking behavior that doesn't support aliases by
+        # default. Explicitly enable aliases if the option is available.
+        yaml =
+          begin
+            YAML.load_file(file, aliases: true)
+          rescue ArgumentError
+            YAML.load_file(file)
           end
 
+        hash = yaml ? yaml.to_hash : {}
         Overcommit::Configuration.new(hash, options)
       end
     end