diff options
Diffstat (limited to 'lib/gitlab/changelog/ast.rb')
| -rw-r--r-- | lib/gitlab/changelog/ast.rb | 157 |
1 files changed, 0 insertions, 157 deletions
diff --git a/lib/gitlab/changelog/ast.rb b/lib/gitlab/changelog/ast.rb deleted file mode 100644 index 2c787d396f5..00000000000 --- a/lib/gitlab/changelog/ast.rb +++ /dev/null @@ -1,157 +0,0 @@ -# frozen_string_literal: true - -module Gitlab - module Changelog - # AST nodes to evaluate when rendering a template. - # - # Evaluating an AST is done by walking over the nodes and calling - # `evaluate`. This method takes two arguments: - # - # 1. An instance of `EvalState`, used for tracking data such as the number - # of nested loops. - # 2. An object used as the data for the current scope. This can be an Array, - # Hash, String, or something else. It's up to the AST node to determine - # what to do with it. - # - # While tree walking interpreters (such as implemented here) aren't usually - # the fastest type of interpreter, they are: - # - # 1. Fast enough for our use case - # 2. Easy to implement and maintain - # - # In addition, our AST interpreter doesn't allow for arbitrary code - # execution, unlike existing template engines such as Mustache - # (https://github.com/mustache/mustache/issues/244) or ERB. - # - # Our interpreter also takes care of limiting the number of nested loops. - # And unlike Liquid, our interpreter is much smaller and thus has a smaller - # attack surface. Liquid isn't without its share of issues, such as - # https://github.com/Shopify/liquid/pull/1071. - # - # We also evaluated using Handlebars using the project - # https://github.com/SmartBear/ruby-handlebars. Sadly, this implementation - # of Handlebars doesn't support control of whitespace - # (https://github.com/SmartBear/ruby-handlebars/issues/37), and the project - # didn't appear to be maintained that much. - # - # This doesn't mean these template engines aren't good, instead it means - # they won't work for our use case. For more information, refer to the - # comment https://gitlab.com/gitlab-org/gitlab/-/merge_requests/50063#note_469293322. - module AST - # An identifier in a selector. - Identifier = Struct.new(:name) do - def evaluate(state, data) - return data if name == 'it' - - data[name] if data.is_a?(Hash) - end - end - - # An integer used in a selector. - Integer = Struct.new(:value) do - def evaluate(state, data) - data[value] if data.is_a?(Array) - end - end - - # A selector used for loading a value. - Selector = Struct.new(:steps) do - def evaluate(state, data) - steps.reduce(data) do |current, step| - break if current.nil? - - step.evaluate(state, current) - end - end - end - - # A tag used for displaying a value in the output. - Variable = Struct.new(:selector) do - def evaluate(state, data) - selector.evaluate(state, data).to_s - end - end - - # A collection of zero or more expressions. - Expressions = Struct.new(:nodes) do - def evaluate(state, data) - nodes.map { |node| node.evaluate(state, data) }.join('') - end - end - - # A single text node. - Text = Struct.new(:text) do - def evaluate(*) - text - end - end - - # An `if` expression, with an optional `else` clause. - If = Struct.new(:condition, :true_body, :false_body) do - def evaluate(state, data) - result = - if truthy?(condition.evaluate(state, data)) - true_body.evaluate(state, data) - elsif false_body - false_body.evaluate(state, data) - end - - result.to_s - end - - def truthy?(value) - # We treat empty collections and such as false, removing the need for - # some sort of `if length(x) > 0` expression. - value.respond_to?(:empty?) ? !value.empty? : !!value - end - end - - # An `each` expression. - Each = Struct.new(:collection, :body) do - def evaluate(state, data) - values = collection.evaluate(state, data) - - return '' unless values.respond_to?(:each) - - # While unlikely to happen, it's possible users attempt to nest many - # loops in order to negatively impact the GitLab instance. To make - # this more difficult, we limit the number of nested loops a user can - # create. - state.enter_loop do - values.map { |value| body.evaluate(state, value) }.join('') - end - end - end - - # A class for transforming a raw Parslet AST into a more structured/easier - # to work with AST. - # - # For more information about Parslet transformations, refer to the - # documentation at http://kschiess.github.io/parslet/transform.html. - class Transformer < Parslet::Transform - rule(ident: simple(:name)) { Identifier.new(name.to_s) } - rule(int: simple(:name)) { Integer.new(name.to_i) } - rule(text: simple(:text)) { Text.new(text.to_s) } - rule(exprs: subtree(:nodes)) { Expressions.new(nodes) } - rule(selector: sequence(:steps)) { Selector.new(steps) } - rule(selector: simple(:step)) { Selector.new([step]) } - rule(variable: simple(:selector)) { Variable.new(selector) } - rule(each: simple(:values), body: simple(:body)) do - Each.new(values, body) - end - - rule(if: simple(:cond), true_body: simple(:true_body)) do - If.new(cond, true_body) - end - - rule( - if: simple(:cond), - true_body: simple(:true_body), - false_body: simple(:false_body) - ) do - If.new(cond, true_body, false_body) - end - end - end - end -end |