Commit 4a1c740c authored by Rene Saarsoo's avatar Rene Saarsoo
Browse files

Start implementing FunctionAst class. 

To auto-detect return types of functions from source code.

This version is able to auto-detect if a simple function without any
control flow statements returns this.
parent 564f7871

lib/jsduck/function_ast.rb

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require "jsduck/serializer"

require "jsduck/evaluator"



module JsDuck



  # Analyzes the AST of a FunctionDeclaration or FunctionExpression.

  class FunctionAst

    # Detects from function body what the function returns.

    def returns(ast)

      if ast && function?(ast)

        body_returns(ast["body"]["body"])

      else

        nil

      end

    end



    private



    def function?(ast)

      ast["type"] == "FunctionDeclaration" || ast["type"] == "FunctionExpression"

    end



    def body_returns(body)

      body = skip_non_control_flow_statements(body)



      if body.length > 0 && return_this?(body[0])

        "this"

      else

        nil

      end

    end



    def return_this?(ast)

      return?(ast) && this?(ast["argument"])

    end



    def return?(ast)

      ast["type"] == "ReturnStatement"

    end



    def this?(ast)

      ast["type"] == "ThisExpression"

    end



    def skip_non_control_flow_statements(statements)

      i = statements.find_index {|s| control_flow?(s) }

      if i

        statements.slice(i, statements.length)

      else

        []

      end

    end



    def control_flow?(ast)

      [

        "IfStatement",

        "SwitchStatement",

        "ForStatement",

        "ForInStatement",

        "WhileStatement",

        "DoWhileStatement",

        "ReturnStatement",

        "TryStatement",

        "WithStatement",

        "LabeledStatement",

        "BlockStatement",

      ].include?(ast["type"])

    end

  end



end

spec/function_ast_spec.rb

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require "jsduck/js_parser"

require "jsduck/function_ast"



describe "JsDuck::FunctionAst#returns" do

  def returns(string)

    node = JsDuck::JsParser.new(string).parse[0]

    return JsDuck::FunctionAst.new.returns(node[:code])

  end



  it "fails when no AST given at all" do

    returns("/** */").should == nil

  end



  it "fails when no function AST given" do

    returns("/** */ Ext.emptyFn;").should == nil

  end



  it "fails when body has no return statement." do

    returns("/** */ function foo() {}").should == nil

  end



  it "returns this when single return this statement in body" do

    returns("/** */ function foo() {return this;}").should == "this"

  end



  it "returns this when return this after a few expression statements" do

    returns(<<-EOJS).should == "this"

      /** */

      function foo() {

          doSomething();

          i++;

          truthy ? foo() : bar();

          return this;

      }

    EOJS

  end



  it "returns this when return this after a few declarations" do

    returns(<<-EOJS).should == "this"

      /** */

      function foo() {

          var x = 10;

          function blah() {

          }

          return this;

      }

    EOJS

  end



end