[lldb-dev] Using FileCheck in lldb inline tests

Thu Aug 23 16:25:54 PDT 2018

Pinging this because I'd like this to go forward to make testing easier.

I know folks have concerns about maintaining completeness of the scripting APIs and about keeping the test suite debuggable. I just don't think making FileCheck available in inline tests is counter to those goals :).

I think this boils down to having a more powerful replacement for `self.expect` in lldbinline tests. As we're actively discouraging use of pexpect during code review now, we need some replacement.

vedant

> On Aug 15, 2018, at 12:18 PM, Vedant Kumar <vsk at apple.com> wrote:
> 
> 
> 
>> On Aug 15, 2018, at 12:12 PM, Jason Molenda <jmolenda at apple.com> wrote:
>> 
>> 
>> 
>>> On Aug 15, 2018, at 11:34 AM, Vedant Kumar <vsk at apple.com> wrote:
>>> 
>>> 
>>> 
>>>> On Aug 14, 2018, at 6:19 PM, Jason Molenda <jmolenda at apple.com> wrote:
>>>> 
>>>> It's more verbose, and it does mean test writers need to learn the public API, but it's also much more stable and debuggable in the future.
>>> 
>>> I'm not sure about this. Having looked at failing sb api tests for a while now, I find them about as easy to navigate and fix as FileCheck tests in llvm.
>> 
>> I don't find that to be true.  I see a failing test on line 79 or whatever, and depending on what line 79 is doing, I'll throw in some self.runCmd("bt")'s or self.runCmd("fr v") to the test, re-run, and see what the relevant context is quickly. For most simple tests, I can usually spot the issue in under a minute.  dotest.py likes to eat output when it's run in multiprocess mode these days, so I have to remember to add --no-multiprocess.  If I'm adding something that I think is generally useful to debug the test case, I'll add a conditional block testing again self.TraceOn() and print things that may help people who are running dotest.py with -t trace mode enabled.
> 
> I do agree that there are effective ways of debugging sb api tests. Having worked with plenty of filecheck-based tests in llvm/clang/swift, I find them to be as easy (or easier for me personally) to debug.
> 
> 
>> Sometimes there is a test written so it has a "verify this value" function that is run over a variety of different variables during the test timeframe, and debugging that can take a little more work to understand the context that is failing.  But that kind of test would be harder (or at least much more redundant) to express in a FileCheck style system anyway, so I can't ding it.
> 
> 
> Yep, sounds like a great candidate for a unit test or an SB API test.
> 
> 
>> As for the difficulty of writing SB API tests, you do need to know the general architecture of lldb (a target has a process, a process has threads, a thread has frames, a frame has variables), the public API which quickly becomes second nature because it is so regular, and then there's the testsuite specific setup and template code.  But is that that intimidating to anyone familiar with lldb?
> 
> Not intimidating, no. Cumbersome and slow, absolutely. So much so that I don't see a way of adequately testing my patches this way. It would just take too much time.
> 
> vedant
> 
>> packages/Python/lldbsuite/test/sample_test/TestSampleTest.py is 50 lines including comments; there's about ten lines of source related to initializing / setting up the testsuite, and then 6 lines is what's needed to run to a breakpoint, get a local variable, check the value. 
>> 
>> 
>> J
>> 
>> 
>> 
>>> 
>>> 
>>>> It's a higher up front cost but we're paid back in being able to develop lldb more quickly in the future, where our published API behaviors are being tested directly, and the things that must not be broken.
>>> 
>>> I think the right solution here is to require API tests when new functionality is introduced. We can enforce this during code review. Making it impossible to write tests against the driver's output doesn't seem like the best solution. It means that far fewer tests will be written (note that a test suite run of lldb gives less than 60% code coverage). It also means that the driver's output isn't tested as much as it should be.
>>> 
>>> 
>>>> The lldb driver's output isn't a contract, and treating it like one makes the debugger harder to innovate in the future.
>>> 
>>> I appreciate your experience with this (pattern matching on driver input) in gdb. That said, I think there are reliable/maintainable ways to do this, and proven examples we can learn from in llvm/clang/etc.
>>> 
>>> 
>>>> It's also helpful when adding new features to ensure you've exposed the feature through the API sufficiently.  The first thing I thought to try when writing the example below was SBFrame::IsArtificial() (see SBFrame::IsInlined()) which doesn't exist.  If a driver / IDE is going to visually indicate artificial frames, they'll need that.
>>> 
>>> Sure. That's true, we do need API exposure for new features, and again we can enforce that during code review. The reason you didn't find IsArtificial() is because it's sitting on my disk :). Haven't shared the patch yet.
>>> 
>>> vedant
>>> 
>>>> 
>>>> J
>>>> 
>>>>> On Aug 14, 2018, at 5:56 PM, Vedant Kumar <vsk at apple.com> wrote:
>>>>> 
>>>>> It'd be easy to update FileCheck tests when changing the debugger (this happens all the time in clang/swift). OTOH, the verbosity of the python API means that fewer tests get written. I see a real need to make expressive tests easier to write.
>>>>> 
>>>>> vedant
>>>>> 
>>>>>> On Aug 14, 2018, at 5:38 PM, Jason Molenda <jmolenda at apple.com> wrote:
>>>>>> 
>>>>>> I'd argue against this approach because it's exactly why the lit tests don't run against the lldb driver -- they're hardcoding the output of the lldb driver command into the testsuite and these will eventually make it much more difficult to change and improve the driver as we've accumulated this style of test.
>>>>>> 
>>>>>> This is a perfect test for a normal SB API.  Run to your breakpoints and check the stack frames.
>>>>>> 
>>>>>> f0 = thread.GetFrameAtIndex(0)
>>>>>> check that f0.GetFunctionName() == sink
>>>>>> check that f0.IsArtifical() == True
>>>>>> check that f0.GetLineEntry().GetLine() == expected line number
>>>>>> 
>>>>>> 
>>>>>> it's more verbose, but it's also much more explicit about what it's checking, and easy to see what has changed if there is a failure.
>>>>>> 
>>>>>> 
>>>>>> J
>>>>>> 
>>>>>>> On Aug 14, 2018, at 5:31 PM, Vedant Kumar via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>>>>>>> 
>>>>>>> Hello,
>>>>>>> 
>>>>>>> I'd like to make FileCheck available within lldb inline tests, in addition to existing helpers like 'runCmd' and 'expect'.
>>>>>>> 
>>>>>>> My motivation is that several tests I'm working on can't be made as rigorous as they need to be without FileCheck-style checks. In particular, the 'matching', 'substrs', and 'patterns' arguments to runCmd/expect don't allow me to verify the ordering of checked input, to be stringent about line numbers, or to capture & reuse snippets of text from the input stream.
>>>>>>> 
>>>>>>> I'd curious to know if anyone else is interested or would be willing to review this (https://reviews.llvm.org/D50751).
>>>>>>> 
>>>>>>> Here's an example of an inline test which benefits from FileCheck-style checking. This test is trying to check that certain frames appear in a backtrace when stopped inside of the "sink" function. Notice that without FileCheck, it's not possible to verify the order in which frames are printed, and that dealing with line numbers would be cumbersome.
>>>>>>> 
>>>>>>> ```
>>>>>>> --- a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
>>>>>>> +++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
>>>>>>> @@ -9,16 +9,21 @@
>>>>>>> 
>>>>>>> volatile int x;
>>>>>>> 
>>>>>>> +// CHECK: frame #0: {{.*}}sink() at main.cpp:[[@LINE+2]] [opt]
>>>>>>> void __attribute__((noinline)) sink() {
>>>>>>> -  x++; //% self.expect("bt", substrs = ['main', 'func1', 'func2', 'func3', 'sink'])
>>>>>>> +  x++; //% self.filecheck("bt", "main.cpp")
>>>>>>> }
>>>>>>> 
>>>>>>> +// CHECK-NEXT: frame #1: {{.*}}func3() {{.*}}[opt] [artificial]
>>>>>>> void __attribute__((noinline)) func3() { sink(); /* tail */ }
>>>>>>> 
>>>>>>> +// CHECK-NEXT: frame #2: {{.*}}func2() at main.cpp:[[@LINE+1]] [opt]
>>>>>>> void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
>>>>>>> 
>>>>>>> +// CHECK-NEXT: frame #3: {{.*}}func1() {{.*}}[opt] [artificial]
>>>>>>> void __attribute__((noinline)) func1() { func2(); /* tail */ }
>>>>>>> 
>>>>>>> +// CHECK-NEXT: frame #4: {{.*}}main at main.cpp:[[@LINE+2]] [opt]
>>>>>>> int __attribute__((disable_tail_calls)) main() {
>>>>>>> func1(); /* regular */
>>>>>>> return 0;
>>>>>>> ```
>>>>>>> 
>>>>>>> For reference, here's the output of the "bt" command:
>>>>>>> 
>>>>>>> ```
>>>>>>> runCmd: bt
>>>>>>> output: * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
>>>>>>> * frame #0: 0x000000010c6a6f64 a.out`sink() at main.cpp:14 [opt]
>>>>>>> frame #1: 0x000000010c6a6f70 a.out`func3() at main.cpp:15 [opt] [artificial]
>>>>>>> frame #2: 0x000000010c6a6f89 a.out`func2() at main.cpp:21 [opt]
>>>>>>> frame #3: 0x000000010c6a6f90 a.out`func1() at main.cpp:21 [opt] [artificial]
>>>>>>> frame #4: 0x000000010c6a6fa9 a.out`main at main.cpp:28 [opt]
>>>>>>> ```
>>>>>>> 
>>>>>>> thanks,
>>>>>>> vedant
>>>>>>> _______________________________________________
>>>>>>> lldb-dev mailing list
>>>>>>> lldb-dev at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev

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