Btw, I think generating them, potentially into several different headers to work around the compile time issue isn't such a bad idea.
On Mon, Sep 14, 2015 at 11:45 PM, Manuel Klimek <kli...@google.com> wrote: > Feel free to rename the AST nodes :) > > On Mon, Sep 14, 2015, 2:44 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 ;-) ). >> >> 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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