[PATCH] Add a level parameter to ClangTidyCheck::diag.

[Alp Toker]

On 03/03/2014 15:34, Alexander Kornienko wrote:
>
> On Mon, Mar 3, 2014 at 4:02 PM, Alp Toker <alp at nuanti.com 
> <mailto:alp at nuanti.com>> wrote:
>
>
>     On 03/03/2014 12:53, Alexander Kornienko wrote:
>
>         On Sun, Mar 2, 2014 at 5:59 PM, Alp Toker <alp at nuanti.com
>         <mailto:alp at nuanti.com> <mailto:alp at nuanti.com
>         <mailto:alp at nuanti.com>>> wrote:
>
>
>             On 02/03/2014 16:18, Alp Toker wrote:
>
>
>                 On 02/03/2014 12:25, Peter Collingbourne wrote:
>
>
>                     Index: clang-tidy/ClangTidy.h
>                    
>         ===================================================================
>                     --- clang-tidy/ClangTidy.h
>                     +++ clang-tidy/ClangTidy.h
>                     @@ -76,7 +76,8 @@
>                         void setContext(ClangTidyContext *Ctx) {
>         Context = Ctx; }
>                           /// \brief Add a diagnostic with the check's
>         name.
>                     -  DiagnosticBuilder diag(SourceLocation Loc,
>         StringRef
>                     Description);
>                     +  DiagnosticBuilder diag(SourceLocation Loc,
>         StringRef
>                     Description,
>                     + DiagnosticIDs::Level Level =
>                     DiagnosticIDs::Warning);
>
>
>                 Could you order the parameters Loc, Level,
>         FormatString and
>                 drop the default argument?
>
>                 That'll provide visual consistency with the output as
>         well as
>                 internal consistency with clang's own
>         getCustomDiagID(Level L,
>                 StringRef FormatString).
>
>                 That way it becomes kind of a shorthand for
>                 diag(getCustomDiagID(...)) << ... which is a step towards
>                 unifying built-in and custom diagnostic IDs.
>
>
>             So it looks like there's a convention of listing the diag
>         Level
>             _after_ the Message clang-tools-extra, and diag(Loc,
>         "message")
>             without specifying a Level. Neither looks like a good idea
>         but if
>             the plan is to keep that convention then I guess your
>         patch is OK.
>
>             It's a failing of clang's diag/tablegen system that it
>         wasn't made
>             reusable and ended up getting re-rolled in external
>         projects, each
>             with slightly different interfaces :-/
>
>
>         Yes, there's a lot to unify and clean up in this area. If we
>         can come up with a proper interface to manage diagnostic ID
>         spaces, so that tablegen'd diagnostic tables can be registered
>         dynamically, I'd be happy to clean up clang-tidy and static
>         analyzer to use this system.
>
>
>     Right on.
>
>
>         In the simplest case, we'd need some analogues for struct
>         StaticDiagInfoRec and maybe struct StaticDiagCategoryRec and a
>         method to register a block of them and return the diagnostic
>         ID of the first element, so that the client code could use it
>         as an offset to the local static IDs.
>
>
>     Agree, but with one significant distinction: It's those
>     "analogues" that created this problem in the first place where we
>     have essentially two parallel diagnostic systems in clang plus
>     another one currently being developed in LLVM core. 
>
>
>     We really need to peel things back at this point so structures
>     like StaticDiag*Rec are shared by built-in and custom diagnostic
>     code paths instead of duplicated.
>
>
> I agree. I just doubt that StaticDiagInfoReg in its current form is 
> generic enough for this purpose. E.g. I strongly doubt, why any plugin 
> or external project would need the SFINAE field.

There's no cost in exposing StaticDiagInfoReg and sharing the structure 
for now.

It's conceivable some Sema plugin will want to emit SFINAE diagnostics 
just as you needed access to WarningOptions but found it to be missing.

On the other hand there is a cost in maintaining parallel structures 
that are "similar but slightly different" because each needs separate 
code paths for handling and emission.

And it's also not clear why SFINAE was hard-coded into the structure in 
the first place -- it could just as well be represented as a regular 
diag group. A quick cleanup would resolve this.


>     They're generic descriptions after all so it might be as
>     straightforward as moving them out of the cpp to a .h file and
>     taking it from there. Ditto getting diag td files to include
>     "Diagnostic.td" instead of the reverse that exists now --
>     otherwise maintaining out-of-tree diagnostic tds is a non-started.
>
>
>     As for registering blocks of diagnostic IDs, that's been kind of
>     unpleasant and doesn't scale well to plugins and external projects.
>
>
> Can you explain why?

Well, why reserve a few hundred IDs here and there, some statically, 
some dynamically that may or may not be used if we don't need to?

Hashing will probably simplify the implementation by not requiring 
upfront decisions on how many diagnostic IDs to pre-allocate to whom, 
especially for things like plugins where we don't know the need.

>     My early thought here is to represent diagnostic IDs as a 32-bit
>     hash of the Rec contents that'll be computed by TableGen at
>     compile time, as well as optionally at runtime for diagnostics
>     that need to be defined dynamically. Should solve various quirks
>     that are getting swept under the carpet today.
>
>
> What are you going to do with collisions?

With categories included in the hash they won't collide unless there's a 
genuine bug like multiple initialization or mistakenly duplicated 
diagnostics. Which is a neat property.

Alp.




>
>         What do you think about this?
>
>
>     Keen to go ahead with it so long as we're treating the work as
>     much-needed cleanup, with clang-tools-extra getting the
>     functionality when it's ready. It is a non-trivial but the
>     reduction in cruft and will surely pay off.
>
>
>     Alp.
>
>     -- 
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>

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