module Rake
# InvocationChain tracks the chain of task invocations to detect
# circular dependencies.
class InvocationChain < LinkedList
# Is the invocation already in the chain?
def member?(invocation)
head == invocation || tail.member?(invocation)
end
# Append an invocation to the chain of invocations. It is an error
# if the invocation already listed.
def append(invocation)
if member?(invocation)
fail RuntimeError, "Circular dependency detected: #{to_s} => #{invocation}"
end
conj(invocation)
end
# Convert to string, ie: TOP => invocation => invocation
def to_s
"#{prefix}#{head}"
end
# Class level append.
def self.append(invocation, chain)
chain.append(invocation)
end
private
def prefix
"#{tail} => "
end
# Null object for an empty chain.
class EmptyInvocationChain < LinkedList::EmptyLinkedList
@parent = InvocationChain
def member?(obj)
false
end
def append(invocation)
conj(invocation)
end
def to_s
"TOP"
end
end
EMPTY = EmptyInvocationChain.new
end
end
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