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# frozen_string_literal: true
module Gitlab
module Ci
module Pipeline
module Expression
class Parser
ParseError = Class.new(Expression::ExpressionError)
def initialize(tokens)
@tokens = tokens.to_enum
@nodes = []
end
def tree
if Feature.enabled?(:ci_variables_complex_expressions, default_enabled: true)
rpn_parse_tree
else
reverse_descent_parse_tree
end
end
def self.seed(statement)
new(Expression::Lexer.new(statement).tokens)
end
private
# This produces a reverse descent parse tree.
# It does not support precedence of operators.
def reverse_descent_parse_tree
while token = @tokens.next
case token.type
when :operator
token.build(@nodes.pop, tree).tap do |node|
@nodes.push(node)
end
when :value
token.build.tap do |leaf|
@nodes.push(leaf)
end
end
end
rescue StopIteration
@nodes.last || Lexeme::Null.new
end
def rpn_parse_tree
results = []
tokens_rpn.each do |token|
case token.type
when :value
results.push(token.build)
when :operator
right_operand = results.pop
left_operand = results.pop
token.build(left_operand, right_operand).tap do |res|
results.push(res)
end
else
raise ParseError, 'Unprocessable token found in parse tree'
end
end
raise ParseError, 'Unreachable nodes in parse tree' if results.count > 1
raise ParseError, 'Empty parse tree' if results.count < 1
results.pop
end
# Parse the expression into Reverse Polish Notation
# (See: Shunting-yard algorithm)
def tokens_rpn
output = []
operators = []
@tokens.each do |token|
case token.type
when :value
output.push(token)
when :operator
if operators.any? && token.lexeme.precedence >= operators.last.lexeme.precedence
output.push(operators.pop)
end
operators.push(token)
end
end
output.concat(operators.reverse)
end
end
end
end
end
end
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