diff options
Diffstat (limited to 'lib/prism/pattern.rb')
| -rw-r--r-- | lib/prism/pattern.rb | 262 |
1 files changed, 262 insertions, 0 deletions
diff --git a/lib/prism/pattern.rb b/lib/prism/pattern.rb new file mode 100644 index 0000000000..e12cfd597f --- /dev/null +++ b/lib/prism/pattern.rb @@ -0,0 +1,262 @@ +# 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") + + case_match_node = result.value.statements.body.last + raise CompilationError, case_match_node.inspect unless case_match_node.is_a?(CaseMatchNode) + + in_node = case_match_node.conditions.last + raise CompilationError, in_node.inspect unless in_node.is_a?(InNode) + + compile_node(in_node.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(:scan, root) unless block_given? + + @compiled ||= compile + queue = [root] + + while (node = queue.shift) + yield node if @compiled.call(node) # steep:ignore + 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| + key = element.key + if key.is_a?(SymbolNode) + [key.unescaped.to_sym, compile_node(element.value)] + else + raise CompilationError, element.inspect + end + 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 |