Ok. I am happy with this then. (Just personally grumpy having to write cxxRecordDecl(has(cxxConstructorDecl(..))) in the future ;-) ).
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 >> >
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