[PATCH] D54405: Record whether a AST Matcher constructs a Node

[Stephen Kelly via Phabricator via cfe-commits]

steveire added inline comments.


================
Comment at: lib/ASTMatchers/Dynamic/Registry.cpp:77
+      internal::MatcherDescriptor *matchDescriptor, StringRef MatcherName) {
+    auto K = ast_type_traits::ASTNodeKind::getFromNodeKind<
+        typename ast_matchers::internal::VariadicAllOfMatcher<ResultT>::Type>();
----------------
aaron.ballman wrote:
> zturner wrote:
> > steveire wrote:
> > > aaron.ballman wrote:
> > > > steveire wrote:
> > > > > aaron.ballman wrote:
> > > > > > Mildly not keen on the use of `auto` here. It's a factory function, so it kind of names the resulting type, but it also looks like the type will be `ast_matchers::internal::VariadicAllOfMatcher<ResultT>::Type` from the template argument, which is incorrect.
> > > > > There is no reason to assume that taking a template argument means that type is result.
> > > > > 
> > > > > The method is `getFrom` which decreases the ambiguity still further.
> > > > > 
> > > > > Spelling out the type doesn't add anything useful. This should be ok.
> > > > > There is no reason to assume that taking a template argument means that type is result.
> > > > 
> > > > Aside from all the other places that do exactly that (getAs<>, cast<>, dyn_cast<>, castAs<>, and so on). Generally, when we have a function named get that takes a template type argument, the result when seen in proximity to auto is the template type.
> > > > 
> > > > > Spelling out the type doesn't add anything useful. This should be ok.
> > > > 
> > > > I slept on this one and fall on the other side of it; using auto hides information that tripped up at least one person when reading the code, so don't use auto. It's not clear enough what the resulting type will be.
> > > I put this in the category of requiring 
> > > 
> > >     SomeType ST = SomeType::create();
> > > 
> > > instead of 
> > > 
> > >     auto ST = SomeType::create();
> > > 
> > > `ast_type_traits::ASTNodeKind` is already on that line and you want to see it again.
> > > 
> > FWIW I'm with Aaron here.  Im' not familiar at all with this codebase, and looking at the code, my first instinct is "the result type is probably `ast_matchers::internal::VariadicAllOfMatcher<ResultT>::Type`".  According to Aaron's earlier comment, that is incorrect, so there's at least 1 data point that it hinders readability.
> > 
> > So, honest question.  What *is* the return type here?
> > So, honest question. What *is* the return type here?
> 
> Much to my surprise, it's `ASTNodeKind`. It was entirely unobvious to me that this was a factory function.
@zturner Quoting myself:

> `ast_type_traits::ASTNodeKind` is already on that line and you want to see it again.

The expression is `getFromNodeKind`. There is a pattern of `SomeType::fromFooKind<FooKind>()` returning a `SomeType`. This is not so unusual.




Repository:
  rC Clang

https://reviews.llvm.org/D54405