[llvm-dev] [RFC] Preferred error/note style across non-clang tools, e.g. tablegen

[Evandro Menezes via llvm-dev]

> On Jul 22, 2020, at 18:09, Jonathan Roelofs <jonathan_roelofs at apple.com> wrote:
> 
> 
> 
>> On Jul 22, 2020, at 4:31 PM, Evandro Menezes <evandro.menezes at sifive.com <mailto:evandro.menezes at sifive.com>> wrote:
>>> Sure, let’s talk about what that end goal should be! Can you give some other examples of where these inconsistencies could be improved?
>> 
>> None specifically comes to the top of my mind, but they are legion, which I suppose there's no disagreement about it.  I myself committed a few small patches to improve error reporting as I came along them.  In many cases, merely adding the file name or line number where the error was found.
>> 
>> Then again, as Matt mentioned, TableGen prefers to assert instead of erring out, which is quite unhelpful.  In this sense, by all means, an incremental improvement over an assert is more than incremental, but essential.
>> 
>>>>  If one wants to improve the error reporting in TableGen, let one take it on himself this project, apart from one's other patches.
>>> 
>>> Is incremental progress not welcome? I understand pushback on refactoring combined with functional changes, but that’s not at all what this is. The entire purpose of that patch is to improve these diagnostics, making it easier to do scheduler model work.
>> 
>> My concern is that without a definition of the intended style of the error messages, as they are incrementally modified, they will be changed inconsistently.  
>> 
>> IMO, the error messages should provide some minimum information to be useful:
>> - Offending file
>> - Offending line number
>> - Offending structure (e.g., resource type, instruction name, etc)
>> - Offense
> 
> Agreed. This is a good minimum.
> 
> Sometimes there are cases where the offense is a conflict between two definitions, and in a lot of other tooling this is represented as a note that points at the other definition. This helps because it gives you some context around the two definitions in a way that appending the file + line number to the error message doesn’t.

Understood.

>> I do not personally like the error and note, since in the patch above, the note is always fatal, whereas I'd rather see what other errors there are before it aborts.
> 
> There is plenty of prior-art even just in CodeGenSchedule for error-and-non-fatal-notes (see collectRetireControlUnits, collectLoadStoreQueueInfo). These new ones merely maintain existing behavior of exiting after the diagnostic. Seems this objection is an objection to how it already behaves, and not to the changes I’m proposing.

I may be missing something, but we'll discuss the patch in its review.  However, unless an error results in a barrage of errors because something crucial was broken, I'd rather see all error messages.  Sometimes, building is tedious (e.g., batch system), so I'd rather be aware of all issues and fix them before trying another build.

Thank you,

__ 
Evandro Menezes ◊ SiFive ◊ Austin, TX

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