s/exists?/symlink?/ + remove useless check + remove useless call to a function.

src/dodb/index.cr

@@ -19,11 +19,12 @@ class DODB::Index(V) < DODB::Indexer(V)
 
 		symlink = file_path_index index_key.to_s
 
-		# FIXME: Check it’s not pointing to “old_value”, if any, before raising.
-		if ::File.exists? symlink
+		if ::File.symlink? symlink
+			# In case both old and new values are pointing to the same key,
+			# this is not considered a collision.
 			if old_value
 				old_key = key_proc.call old_value
-				return if symlink == file_path_index old_key.to_s
+				return if index_key == old_key
 			end
 
 			raise IndexOverload.new "index '#{@name}' is overloaded for key '#{key}', file #{symlink} exists"
@@ -39,11 +40,6 @@ class DODB::Index(V) < DODB::Indexer(V)
 
 		Dir.mkdir_p ::File.dirname symlink
 
-		# FIXME: Now that this is done in check!, can we remove it?
-		if ::File.exists? symlink
-			raise Exception.new "symlink already exists: #{symlink}"
-		end
-
 		::File.symlink get_data_symlink_index(key), symlink
 	end
 
@@ -96,9 +92,7 @@ class DODB::Index(V) < DODB::Indexer(V)
 
 	def get_key_on_fs(index : String) : Int32
 		file_path = file_path_index index
-
-		raise MissingEntry.new(@name, index) unless ::File.exists? file_path
-
+		raise MissingEntry.new(@name, index) unless ::File.symlink? file_path
 		::File.readlink(file_path).sub(/^.*\//,   "").to_i
 	end
 
@@ -158,8 +152,9 @@ class DODB::CachedIndex(V) < DODB::Index(V)
 	def check!(key, value, old_value)
 		index_key = key_proc.call value
 
-		# FIXME: Check it’s not pointing to “old_value”, if any, before raising.
 		if data[index_key]?
+			# In case both old and new values are pointing to the same key,
+			# this is not considered a collision.
 			if old_value
 				old_key = key_proc.call old_value
 				return if index_key == old_key

src/dodb/tags.cr

@@ -62,11 +62,12 @@ class DODB::Tags(V) < DODB::Indexer(V)
 		return r_value if keys.size < 1
 
 		first_key = keys.pop
-		r_value = get_with_indice(first_key) rescue return [] of Tuple(V, Int32)
+		r_value = get_with_indice(first_key) rescue return r_value
 
 		keys.each do |tag|
 			values = get_with_indice(tag) rescue return [] of Tuple(V, Int32)
 			r_value &= values
+			return r_value if r_value.size < 1
 		end
 		r_value
 	end