[lldb-dev] LLDB Evolution

Zachary Turner via lldb-dev lldb-dev at lists.llvm.org
Mon Aug 8 14:57:27 PDT 2016

On Mon, Aug 8, 2016 at 2:40 PM Kate Stone via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> LLDB has come a long way since the project was first announced.  As a
> robust debugger for C-family languages and Swift, LLDB is constantly in use
> by millions of developers.  It has also become a foundation for bringing up
> debugger support for other languages like Go and RenderScript.  In addition
> to the original macOS implementation the Linux LLDB port is in active use
> and Windows support has made significant strides.  IDE and editor
> integration via both SB APIs and MI have made LLDB available to even more
> users.  It’s definitely a project every contributor can be proud of and I’d
> like to take a moment to thank everyone who has been involved in one way or
> another.
> It’s also a project that shows some signs of strain due to its rapid
> growth.  We’ve accumulated some technical debt that must be paid off, and
> in general it seems like a good time to reflect on where we'll be headed
> next.  We’ve outlined a few goals for discussion below as well as one more
> short-term action.  Discussion is very much encouraged.
> *Forward-Looking Goals*
>    1. Testing Strategy Evaluation
> Keeping our code base healthy is next to impossible without a robust
> testing strategy.  Our existing suite of tests is straightforward to run
> locally, and serves as a foundation for continuous integration.  That said,
> it is definitely not exhaustive.  Obvious priorities for improvement
> include gathering coverage information, investing in more conventional unit
> tests in addition to the suite of end-to-end tests, and introducing tests
> in code bases where we depend on debugger-specific behavior (e.g.: for
> expression evaluation.)
> I know this is going to be controversial, but I think we should at least
do a serious evaluation of whether using the lit infrastructure would work
for LLDB.  Conventional wisdom is that it won't work because LLDB tests are
fundamentally different than LLVM tests.  I actually completely agree with
the latter part.  They are fundamentally different.

However, we've seen some effort to move towards lldb inline tests, and in a
sense that's conceptually exactly what lit tests are.  My concern is that
nobody with experience working on LLDB has a sufficient understanding of
what lit is capable of to really figure this out.

I know when I mentioned this some months ago Jonathan Roelofs chimed in and
said that he believes lit is extensible enough to support LLDB's use case.
The argument -- if I remember it correctly -- is that the traditional view
of what a lit test (i.e. a sequence of commands that checks the output of a
program against expected output) is one particular implementation of a
lit-style test.  But that you can make your own which do whatever you want.

This would not just be busy work either.  I think everyone involved with
LLDB has experienced flakiness in the test suite.  Sometimes it's flakiness
in LLDB itself, but sometimes it is flakiness in the test infrastructure.
It would be nice to completely eliminate one source of flakiness.

I think it would be worth having some LLDB experts sit down in person with
some lit experts and brainstorm ways to make LLDB use lit.

Certainly it's worth a serious look, even if nothing comes of it.

>    4. Good Citizenship in the LLVM Community
> Last, but definitely not least, LLDB should endeavor to be a good citizen
> of the LLVM community.  We should encourage developers to think of the
> technology stack as a coherent effort, where common code should be
> introduced at an appropriate level in the stack.  Opportunities to factor
> reusable aspects of the LLDB code base up the stack into LLVM will be
> pursued.
> One arbitrary source of inconsistency at present is LLDB’s coding
> standard.  That brings us to…
> *Near-Term Goal: Standardizing on LLVM-style clang-format Rules*
> We’ve heard from several in the community that would prefer to have a
> single code formatting style to further unify the two code bases.  Using
> clang-format with the default LLVM conventions would simplify code
> migration, editor configuration, and coding habits for developers who work
> in multiple LLVM projects.  There are non-trivial implications to
> reformatting a code base with this much history.  It can obfuscate history
> and impact downstream projects by complicating merges.  Ideally, it should
> be done once with as much advance notice as is practical.  Here’s the
> timeline we’re proposing:
> *Today* - mechanical reformatting proposed, comment period begins
> To get a preview of what straightforward reformatting of the code looks
> like, just follow these steps to get a clean copy of the repository and
> reformat it:
>    1. Check out a clean copy of the existing repository
>    2. Edit .clang-format in the root of the tree, remove all but the line
>    “BasedOnStyle: LLVM”
>    3. Change your current working directory to the root of the tree to
>    reformat
>    4. Double-check to make sure you did step 3 ;-)
>    5. Run the following shell command: "find . -name "*.[c,cpp,h] -exec
>    clang-format -i {} +"
> Very excited about this one, personally.  While I have my share of qualms
with LLVM's style, the benefit of having consistency is hard to overstate.
It greatly reduces the effort to switch between codebases, a direct
consequence of which is that it encourages people with LLVM expertise to
jump into the LLDB codebase, which hopefully can help to tear down the
invisible wall between the two.

As a personal aside, this allows me to go back to my normal workflow of
having 3 edit source files opened simultaneously and tiled horizontally,
which is very nice.
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