On Mon, Sep 14, 2015 at 5:44 PM, Daniel Jasper <djas...@google.com> wrote: > Ok. I am happy with this then. > > (Just personally grumpy having to write > cxxRecordDecl(has(cxxConstructorDecl(..))) in the future ;-) ).
I share your grumpiness about the cxxConstructorDecl, but probably won't share it when we add objcConstructorDecl or some crazy thing. :-P I will get started on this and come back with a patch. Thank you all for the conversation! ~Aaron > > On Mon, Sep 14, 2015 at 11:41 PM, Manuel Klimek <kli...@google.com> wrote: >> >> >> >> On Mon, Sep 14, 2015 at 2:29 PM Aaron Ballman <aa...@aaronballman.com> >> wrote: >>> >>> On Mon, Sep 14, 2015 at 4:38 PM, Manuel Klimek <kli...@google.com> wrote: >>> > >>> > >>> > On Mon, Sep 14, 2015 at 12:26 PM Aaron Ballman <aa...@aaronballman.com> >>> > wrote: >>> >> >>> >> On Mon, Sep 14, 2015 at 2:45 PM, Daniel Jasper <djas...@google.com> >>> >> wrote: >>> >> > By this point, I see that change might be profitable overall. >>> >> > However, >>> >> > lets >>> >> > completely map this out. Changing just cxxRecordDecl() can actually >>> >> > increase >>> >> > confusion in other areas. Right now, not a single AST matcher has >>> >> > the >>> >> > cxx >>> >> > prefix (although a total of 28 stand for the corresponding CXX.. AST >>> >> > node). >>> >> > This is consistent and people knowing this will never try to write >>> >> > cxxConstructExpr(). As soon as people have used cxxRecordDecl(), the >>> >> > chance >>> >> > of them trying cxxConstructExpr() increases. You have spent a long >>> >> > time >>> >> > figuring out that recordDecl means cxxRecordDecl(), which is one >>> >> > datapoint, >>> >> > but I am not aware of anyone else having this specific issue. And we >>> >> > could >>> >> > make this less bad with better documentation, I think. >>> >> > >>> >> > So, for me, the questions are: >>> >> > 1) Do we want/need this change? >>> >> >>> >> We definitely need *a* change because there currently is no way to >>> >> match a C struct or union when compiling in C mode. I discovered this >>> >> because I was trying to write a new checker for clang-tidy that >>> >> focuses on C code and it would fail to match when compiling in C mode. >>> >> Whether we decide to go with cxxRecordDecl vs recordDecl vs structDecl >>> >> (etc) is less important to me than the ability to write clang-tidy >>> >> checks for C code. >>> >> >>> >> > 2) Do we want to be consistent and change the other 27 matchers as >>> >> > well? >>> >> >>> >> I'm on the fence about this for all the reasons you point out. >>> >> >>> >> > A fundamental question is whether we want AST matchers to match AST >>> >> > nodes >>> >> > 1:1 or whether they should be an abstraction from some >>> >> > implementation >>> >> > details of the AST. >>> >> >>> >> I absolutely agree that this is a fundamental question. I think a >>> >> higher priority fundamental question that goes along with it is: are >>> >> we okay with breaking a lot of user code (are these meant to be stable >>> >> APIs like the LLVM C APIs)? If we want these APIs to be stable, that >>> >> changes the answer of what kind of mapping we can have. >>> > >>> > >>> > I think the AST matchers are so closely coupled to the AST that it >>> > trying to >>> > be more stable than the AST doesn't help. Basically all uses of AST >>> > matchers >>> > do something with the AST nodes afterwards, which will break anyway. >>> >>> I can get behind that logic. So we're okay with breaking their code >>> because there's no way around it -- it's tied to the AST, so users >>> cannot rely on the AST APIs remaining the same from release to release >>> anyway. >> >> >> We might even *want* the code to break, as the use of the AST node might >> now be incorrect on a semantic level. >> >>> >>> >>> > >>> >> >>> >> > And this is not an easy question to answer. There are >>> >> > many places where we don't follow a strict 1:1 mapping. Mostly node >>> >> > matchers, but also in traversal matchers, e.g. isDerivedFrom(). >>> >> > >>> >> > Personally, I'd really hate to have the cxx Prefix everywhere, but >>> >> > that's >>> >> > just my personal opinion. I would even prefer matchers like record() >>> >> > and >>> >> > method(), but I think somebody convinced me that that would be a >>> >> > very >>> >> > bad >>> >> > idea ;-). >>> >> >>> >> My personal opinion is that (1) breaking code is fine, but we should >>> >> avoid doing it without very clear benefit, and (2) the mapping between >>> >> AST node identifiers and AST matcher identifiers needs to be >>> >> incredibly obvious, but perhaps not slavishly 1:1. If we instead >>> >> decide we want a 1:1 mapping, then I think we need to start seriously >>> >> considering auto-generating the AST node (and type) matchers from >>> >> tablegen so that the AST nodes *cannot* get out of sync with the AST >>> >> matchers, otherwise we'll be right back here again in a few years when >>> >> we modify the name of an AST node. >>> > >>> > >>> > I do think we want to auto-generate the matchers, but I don't think >>> > tablegen >>> > is the right approach (I think an ast-matcher based tool is ;) >>> > That said, auto-generating all the matchers is a) a lot of effort and >>> > b) the >>> > code-size and compile time of matchers already matters, so it's unclear >>> > which ones we would want to generate, especially for traversal matchers >>> > :( >>> >>> Oh, that's an excellent point (I'm talking about (b), I already knew >>> (a) was a lot of work). Thank you for pointing that out! >>> >>> > >>> >> >>> >> My definition of "incredibly obvious" is: if the AST has a prefixed >>> >> and unprefixed version, or two different prefixes, we should mimic >>> >> that directly with the matchers. Otherwise, existing AST matchers >>> >> without prefix shenanigans can remain as they are, and new AST >>> >> matchers should prefix as-required. If we decide we're okay breaking >>> >> code, then I don't see a problem with changing ctorInitializer() into >>> >> cxxCtorInitializer() when C adds constructors. ;-) >>> > >>> > >>> > I think the main things is cost for developers who try to write >>> > matchers and >>> > work from the -ast-dump. Figuring out that there *is* a matcher with an >>> > unprefixed node can take a while. >>> >>> Hmm, yes, but "take a while" should be relatively short, I would >>> think. In that use-case, the user does an -ast-dump, sees >>> "CXXFrobbleGnasher", they go to the AST matcher reference and they >>> search for "CXXFrobberGnasher." The first hit won't be >>> cxxFrobbleGnasher, but the entry for frobbleGnasher (which is still >>> the first hit when searching from the top of the document due to the >>> way we position node matchers) will have a parameter of >>> CXXFrobbleGnasher, so they will find still get to the right matcher on >>> the first hit. If someone doesn't read the documentation at all, >>> they're going to try cxxFrobbleGnasher() and get a compile error/no >>> known matcher. Then they'll go look at ASTMatchers.h and figure out >>> it's called frobbleGnasher by searching there instead of the >>> documentation. >> >> >> The problem is that I've learned that sometimes people try to make things >> work in ways that I couldn't even imagine, and they lose more time than I >> could ever imagine them using :) Also, I agree the time is probably on >> average not that large, but we pay it over a long time in the future, and it >> tends to add up. >> >>> >>> That's compared to having the matcher name always be the same as the >>> AST node, where the user writes cxxFrobbleGnasher and it just works, >>> which is definitely a mark in favor of making everything consistent. I >>> just don't think the current approach is too onerous in the case where >>> the matcher is at least *provided* for the user with a relatively sane >>> name. >>> >>> >> I should be clear, I'm not opposed to just having a 1:1 mapping. I'm >>> >> just not certain the benefits of being strict about that outweigh the >>> >> costs to broken code. cxxCtorInitializer will break someone's code, >>> >> but I don't think it adds any clarity to their code, so I don't see >>> >> the benefit of forcing the change. >>> > >>> > Well, I think there's the cost of broken code *once* now, vs. the >>> > (smaller) >>> > cost for users in all future. >>> > I'm still strongly in favor of breaking now, and having a simpler model >>> > going forward. >>> >>> I'm definitely in favor of breaking now in the case of RecordDecl vs >>> CXXRecordDecl. I think having recordDecl match CXXRecordDecl is a bug >>> given that there's no way to match a RecordDecl. >>> >>> I would also be totally in favor of being consistent if we were >>> starting from scratch. I'm very, very weakly opposed to breaking more >>> user's code than we have to in order to get usable matchers because it >>> seems gratuitous. Breaking code to get something that works seems >>> reasonable. Breaking code that already works just to change the name >>> for consistency elsewhere, I'm a bit less keen on. But the fact that >>> we already can break user's code at-will because of the reliance on >>> the AST nodes makes me think it may be the right approach for the best >>> API, since that's what I would want if we were starting from scratch. >>> >>> Okay, I'm convinced. I think we should rename the type and node >>> matchers (not traversal and narrowing matchers) to match the AST node >>> names in all cases. We can document the breakage in the release notes, >>> but (hopefully) only have to do this dance one time instead of >>> spreading the pain out as it happens to eventually get to the same >>> place anyway. >> >> >> Yea, people who want more stability do use releases anyway. >> >>> >>> Daniel, is this something you would be okay with? (I'm assuming >>> Richard finds it acceptable based on previous comments from Manuel, >>> but Richard, feel free to chime in.) >> >> >> Offline conversation with Richard says that he is convinced. >> >>> >>> >>> ~Aaron > > _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
