[lldb-dev] Using FileCheck in lldb inline tests

Wed Aug 15 11:34:14 PDT 2018

> 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.

> 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
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>>> 
>> 
> 