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# frozen_string_literal: true
module Prism
# A pattern is an object that wraps a Ruby pattern matching expression. The
# expression would normally be passed to an `in` clause within a `case`
# expression or a rightward assignment expression. For example, in the
# following snippet:
#
# case node
# in ConstantPathNode[ConstantReadNode[name: :Prism], ConstantReadNode[name: :Pattern]]
# end
#
# the pattern is the <tt>ConstantPathNode[...]</tt> expression.
#
# The pattern gets compiled into an object that responds to #call by running
# the #compile method. This method itself will run back through Prism to
# parse the expression into a tree, then walk the tree to generate the
# necessary callable objects. For example, if you wanted to compile the
# expression above into a callable, you would:
#
# callable = Prism::Pattern.new("ConstantPathNode[ConstantReadNode[name: :Prism], ConstantReadNode[name: :Pattern]]").compile
# callable.call(node)
#
# The callable object returned by #compile is guaranteed to respond to #call
# with a single argument, which is the node to match against. It also is
# guaranteed to respond to #===, which means it itself can be used in a `case`
# expression, as in:
#
# case node
# when callable
# end
#
# If the query given to the initializer cannot be compiled into a valid
# matcher (either because of a syntax error or because it is using syntax we
# do not yet support) then a Prism::Pattern::CompilationError will be
# raised.
class Pattern
# Raised when the query given to a pattern is either invalid Ruby syntax or
# is using syntax that we don't yet support.
class CompilationError < StandardError
# Create a new CompilationError with the given representation of the node
# that caused the error.
def initialize(repr)
super(<<~ERROR)
prism was unable to compile the pattern you provided into a usable
expression. It failed on to understand the node represented by:
#{repr}
Note that not all syntax supported by Ruby's pattern matching syntax
is also supported by prism's patterns. If you're using some syntax
that you believe should be supported, please open an issue on
GitHub at https://github.com/ruby/prism/issues/new.
ERROR
end
end
# The query that this pattern was initialized with.
attr_reader :query
# Create a new pattern with the given query. The query should be a string
# containing a Ruby pattern matching expression.
def initialize(query)
@query = query
@compiled = nil
end
# Compile the query into a callable object that can be used to match against
# nodes.
def compile
result = Prism.parse("case nil\nin #{query}\nend")
compile_node(result.value.statements.body.last.conditions.last.pattern)
end
# Scan the given node and all of its children for nodes that match the
# pattern. If a block is given, it will be called with each node that
# matches the pattern. If no block is given, an enumerator will be returned
# that will yield each node that matches the pattern.
def scan(root)
return to_enum(__method__, root) unless block_given?
@compiled ||= compile
queue = [root]
while (node = queue.shift)
yield node if @compiled.call(node)
queue.concat(node.compact_child_nodes)
end
end
private
# Shortcut for combining two procs into one that returns true if both return
# true.
def combine_and(left, right)
->(other) { left.call(other) && right.call(other) }
end
# Shortcut for combining two procs into one that returns true if either
# returns true.
def combine_or(left, right)
->(other) { left.call(other) || right.call(other) }
end
# Raise an error because the given node is not supported.
def compile_error(node)
raise CompilationError, node.inspect
end
# in [foo, bar, baz]
def compile_array_pattern_node(node)
compile_error(node) if !node.rest.nil? || node.posts.any?
constant = node.constant
compiled_constant = compile_node(constant) if constant
preprocessed = node.requireds.map { |required| compile_node(required) }
compiled_requireds = ->(other) do
deconstructed = other.deconstruct
deconstructed.length == preprocessed.length &&
preprocessed
.zip(deconstructed)
.all? { |(matcher, value)| matcher.call(value) }
end
if compiled_constant
combine_and(compiled_constant, compiled_requireds)
else
compiled_requireds
end
end
# in foo | bar
def compile_alternation_pattern_node(node)
combine_or(compile_node(node.left), compile_node(node.right))
end
# in Prism::ConstantReadNode
def compile_constant_path_node(node)
parent = node.parent
if parent.is_a?(ConstantReadNode) && parent.slice == "Prism"
compile_node(node.child)
else
compile_error(node)
end
end
# in ConstantReadNode
# in String
def compile_constant_read_node(node)
value = node.slice
if Prism.const_defined?(value, false)
clazz = Prism.const_get(value)
->(other) { clazz === other }
elsif Object.const_defined?(value, false)
clazz = Object.const_get(value)
->(other) { clazz === other }
else
compile_error(node)
end
end
# in InstanceVariableReadNode[name: Symbol]
# in { name: Symbol }
def compile_hash_pattern_node(node)
compile_error(node) if node.rest
compiled_constant = compile_node(node.constant) if node.constant
preprocessed =
node.elements.to_h do |element|
[element.key.unescaped.to_sym, compile_node(element.value)]
end
compiled_keywords = ->(other) do
deconstructed = other.deconstruct_keys(preprocessed.keys)
preprocessed.all? do |keyword, matcher|
deconstructed.key?(keyword) && matcher.call(deconstructed[keyword])
end
end
if compiled_constant
combine_and(compiled_constant, compiled_keywords)
else
compiled_keywords
end
end
# in nil
def compile_nil_node(node)
->(attribute) { attribute.nil? }
end
# in /foo/
def compile_regular_expression_node(node)
regexp = Regexp.new(node.unescaped, node.closing[1..])
->(attribute) { regexp === attribute }
end
# in ""
# in "foo"
def compile_string_node(node)
string = node.unescaped
->(attribute) { string === attribute }
end
# in :+
# in :foo
def compile_symbol_node(node)
symbol = node.unescaped.to_sym
->(attribute) { symbol === attribute }
end
# Compile any kind of node. Dispatch out to the individual compilation
# methods based on the type of node.
def compile_node(node)
case node
when AlternationPatternNode
compile_alternation_pattern_node(node)
when ArrayPatternNode
compile_array_pattern_node(node)
when ConstantPathNode
compile_constant_path_node(node)
when ConstantReadNode
compile_constant_read_node(node)
when HashPatternNode
compile_hash_pattern_node(node)
when NilNode
compile_nil_node(node)
when RegularExpressionNode
compile_regular_expression_node(node)
when StringNode
compile_string_node(node)
when SymbolNode
compile_symbol_node(node)
else
compile_error(node)
end
end
end
end