RobotFramwork二次开发，微小改动RF，实现while关键字的功能

我们都知道RF里只支持for循环，不支持while循环。或者说，不能造出一个死循环(实际上，while循环就是一个带判断条件的死循环)
而且两种通融的办法也做不到

li=[0,1,2]
for i in li:
  li.append(i)
  # break in some condition

在python里，这样做会导致无限循环。但在RF里，列表在循环前就解析定死，所以对列表的修改并不会影响循环的次数。使用生成器也不能做到

def gen():
  while 1: yield 0

for x in gen():
  ''' do something '''
  # break in some condition

因为生成器没有长度，会导致程序只循环一次就结束

后来发现，其实RF里的命令是一条条执行的，只需要把执行的逻辑修改了即可
在底层库robot\running\steprunner.py下，第33行附近的原文

    def run_steps(self, steps):
        errors = []
        for step in steps:
            try:
                self.run_step(step)
            except ExecutionPassed as exception:
				''''''

在此处step是关键字，steps是一个循环级别内的全部关键字组成的列表。可以改掉for循环为while循环，采用编号来执行step(关键字)。然后增加一个关键字，让其识别到此关键字时，将编号置为0，即直接跳入循环体的顶部即可。具体改为如下

    def run_steps(self, steps):
        errors = []

        cursor = 0  # the index to execute
        keywords = [ str(step).lower() for step in steps ]
        
        while cursor < len(steps):
            try:
                step = steps[cursor]
                if str(step).lower() == "reloop":
                    assert "exit for loop if" in keywords or "exit for loop" in keywords,\
                        "both for loop and exit condition are needed"
                    cursor = 0
                    continue
                cursor += 1
                self.run_step(step)
            except ExecutionPassed as exception:
                ''''''

之后在for循环体结束处使用reloop即可造成死循环，且不会取下一个迭代变量

*** Test Cases ***
while循环
    ${j}    set variable  ${0}
    :for    ${i}    in range    ${1}
    \       ${j}    set variable  ${${j}+1}
    \       exit for loop if      ${j}==${10}
    \       reloop
    log many        done

可以参考我提交的这个链接
https://github.com/robotframework/robotframework/issues/2721

执行结果如下

Starting test: while循环
20190710 20:20:34.127	TRACE	Arguments: [ 0 ]
20190710 20:20:34.127	TRACE	Return: 0
20190710 20:20:34.127	INFO	${j} = 0
20190710 20:20:34.127	TRACE	Arguments: [ 1 ]
20190710 20:20:34.127	TRACE	Return: 1
20190710 20:20:34.128	INFO	${j} = 1
20190710 20:20:34.128	TRACE	Arguments: [ '1==10' ]
20190710 20:20:34.128	TRACE	Return: None
20190710 20:20:34.129	TRACE	Arguments: [ 2 ]
20190710 20:20:34.129	TRACE	Return: 2
20190710 20:20:34.129	INFO	${j} = 2
20190710 20:20:34.129	TRACE	Arguments: [ '2==10' ]
20190710 20:20:34.129	TRACE	Return: None
20190710 20:20:34.130	TRACE	Arguments: [ 3 ]
20190710 20:20:34.130	TRACE	Return: 3
20190710 20:20:34.130	INFO	${j} = 3
20190710 20:20:34.130	TRACE	Arguments: [ '3==10' ]
20190710 20:20:34.130	TRACE	Return: None
20190710 20:20:34.131	TRACE	Arguments: [ 4 ]
20190710 20:20:34.131	TRACE	Return: 4
20190710 20:20:34.131	INFO	${j} = 4
20190710 20:20:34.131	TRACE	Arguments: [ '4==10' ]
20190710 20:20:34.131	TRACE	Return: None
20190710 20:20:34.132	TRACE	Arguments: [ 5 ]
20190710 20:20:34.132	TRACE	Return: 5
20190710 20:20:34.132	INFO	${j} = 5
20190710 20:20:34.132	TRACE	Arguments: [ '5==10' ]
20190710 20:20:34.132	TRACE	Return: None
20190710 20:20:34.133	TRACE	Arguments: [ 6 ]
20190710 20:20:34.133	TRACE	Return: 6
20190710 20:20:34.133	INFO	${j} = 6
20190710 20:20:34.133	TRACE	Arguments: [ '6==10' ]
20190710 20:20:34.134	TRACE	Return: None
20190710 20:20:34.134	TRACE	Arguments: [ 7 ]
20190710 20:20:34.134	TRACE	Return: 7
20190710 20:20:34.134	INFO	${j} = 7
20190710 20:20:34.134	TRACE	Arguments: [ '7==10' ]
20190710 20:20:34.135	TRACE	Return: None
20190710 20:20:34.135	TRACE	Arguments: [ 8 ]
20190710 20:20:34.135	TRACE	Return: 8
20190710 20:20:34.135	INFO	${j} = 8
20190710 20:20:34.136	TRACE	Arguments: [ '8==10' ]
20190710 20:20:34.136	TRACE	Return: None
20190710 20:20:34.136	TRACE	Arguments: [ 9 ]
20190710 20:20:34.136	TRACE	Return: 9
20190710 20:20:34.137	INFO	${j} = 9
20190710 20:20:34.137	TRACE	Arguments: [ '9==10' ]
20190710 20:20:34.137	TRACE	Return: None
20190710 20:20:34.138	TRACE	Arguments: [ 10 ]
20190710 20:20:34.138	TRACE	Return: 10
20190710 20:20:34.138	INFO	${j} = 10
20190710 20:20:34.138	TRACE	Arguments: [ '10==10' ]
20190710 20:20:34.139	INFO	Exiting for loop altogether.
20190710 20:20:34.139	TRACE	Arguments: [ 'done' ]
20190710 20:20:34.139	INFO	done
20190710 20:20:34.139	TRACE	Return: None