dgoldman marked 7 inline comments as done.
dgoldman added a comment.

In D83501#2157957 <https://reviews.llvm.org/D83501#2157957>, @sammccall wrote:

> In D83501#2154300 <https://reviews.llvm.org/D83501#2154300>, @dgoldman wrote:
>
> > In D83501#2153605 <https://reviews.llvm.org/D83501#2153605>, @sammccall 
> > wrote:
> >
> > > In D83501#2148671 <https://reviews.llvm.org/D83501#2148671>, @dgoldman 
> > > wrote:
> > >
> > > > I implemented goto-definition from Foo() --> Foo impl in Xrefs, on the 
> > > > symbolcollector side I don't think there's anything to do?
> > >
> > >
> > > This can't be done purely in xrefs as the AST may not be available.
> > >
> > > A.m: `@class Foo; ^Foo x;` <-- go-to-definition at ^
> > >  B.m: `@interface Foo...@end @implementation Foo...@end`
> > >
> > > The index needs to know that for the USR associated with the @class 
> > > (found by targetDecl), the canonical decl is the @interface in B and the 
> > > definition is the @implementation in B.
> > >  So SymbolCollector needs to see it as a definition. **The tests seem to 
> > > show it does already**, but it's not obvious why from the code. Do you 
> > > know? Maybe it's the fact that they share a USR and thus a symbol ID. 
> > > This is worth making explicit somewhere.
> >
> >
> > Think we're talking about different things. See `ObjCClassExtensions` in 
> > SymbolCollectorTests which I added, the idea is that the `Cat ()` can link 
> > to the implementation like I added to XRefs, but I'm not sure how this 
> > should be represented. As for @class -> @interface/@implementation those 
> > should have the same USR, yes.
>
>
> Oh, sorry I indeed missed the parens.
>  Yes, this is a go-to-def special case, SymbolCollector shouldn't need 
> anything. (I'm assuming that a reference to the class is reported already - 
> could add a test that the ref exists if you like).


if I understand this correctly I think `MultipleDeclsWithSameDefinition` 
already tests that, although it relies upon `locateASTReferent` 's 
`TouchedIdentifier` being the interface. Should it always be added instead?



================
Comment at: clang-tools-extra/clangd/XRefs.cpp:276
        getDeclAtPosition(AST, CurLoc, Relations, NodeKind)) {
     // Special case: void foo() ^override: jump to the overridden method.
     if (const auto *CMD = llvm::dyn_cast<CXXMethodDecl>(D)) {
----------------
sammccall wrote:
> dgoldman wrote:
> > sammccall wrote:
> > > dgoldman wrote:
> > > > sammccall wrote:
> > > > > dgoldman wrote:
> > > > > > sammccall wrote:
> > > > > > > dgoldman wrote:
> > > > > > > > sammccall wrote:
> > > > > > > > > dgoldman wrote:
> > > > > > > > > > Think it would make sense to special case ObjCInterfaceDecl 
> > > > > > > > > > here to get at both the interface definition + 
> > > > > > > > > > implementation if available?
> > > > > > > > > Rather than returning both results, I think it's more 
> > > > > > > > > consistent to return them as a declaration/definition pair.
> > > > > > > > > 
> > > > > > > > > (This means special-casing ObjCImplDecl in namedDecl or at 
> > > > > > > > > least getDeclAsPosition, so you always end up with the 
> > > > > > > > > ObjCInterfaceDecl instead)
> > > > > > > > Whoops, meant to comment here but it was lost. I'm not sure 
> > > > > > > > what you meant here. Should this be done here inside the for 
> > > > > > > > loop or in getDeclAtPosition?
> > > > > > > > 
> > > > > > > > Are you saying that given:
> > > > > > > > 
> > > > > > > > ```
> > > > > > > > @interface Foo // A
> > > > > > > > @end
> > > > > > > > @implementation Foo // B
> > > > > > > > @end
> > > > > > > > ```
> > > > > > > > B --> A here
> > > > > > > > 
> > > > > > > > and similarly
> > > > > > > > 
> > > > > > > > ```
> > > > > > > > @interface Foo // A
> > > > > > > > @end
> > > > > > > > @interface Foo (Ext) // B
> > > > > > > > @end
> > > > > > > > @implementation Foo (Ext) // C
> > > > > > > > @end
> > > > > > > > ```
> > > > > > > > B --> A
> > > > > > > > C --> B (and A? it's unclear how this should map over, e.g. 
> > > > > > > > maybe Foo loc --> A, Ext --> B)
> > > > > > > In the first example, selecting either A or B should yield one 
> > > > > > > LocatedSymbol with {Decl=A, Def=B}. This shouldn't require any 
> > > > > > > special-casing.
> > > > > > > 
> > > > > > > The second example is very similar to template specialization, 
> > > > > > > with exceptions:
> > > > > > >  - there's always a Decl/Def pair you may want to navigate 
> > > > > > > between, whereas in templates there rarely is, so we have 
> > > > > > > ambiguity
> > > > > > >  - there's no AST like there is for template names and args, just 
> > > > > > > a bag of tokens
> > > > > > > 
> > > > > > > I'd suggest, given `@interface Foo (Ext)`:
> > > > > > >  - we produce a LocatedSymbol with {Decl=@interface Foo(Ext), 
> > > > > > > Def=@implementation  Foo(Ext)} - this is the default behavior
> > > > > > >  - if the cursor is exactly on the token `Foo`, we also produce a 
> > > > > > > LocatedSymbol with {Decl=@interface Foo, Def=@implementation Foo} 
> > > > > > > - this is similar to the template special case
> > > > > > >  - if the cursor is exactly on the token Ext... are categories 
> > > > > > > explicitly/separately declared anywhere? I guess not. If they 
> > > > > > > are, we could special case this too.
> > > > > > > And `@implementation Foo(Ext)` should behave in exactly the same 
> > > > > > > way.
> > > > > > Trying this out now, two problems:
> > > > > > 
> > > > > > - getDeclAtPosition will call findTarget. Due to the changes above 
> > > > > > we map `ObjCCategoryImplDecl` to its interface. This is OK but then 
> > > > > > when we check for the loc it's obviously != to the impl's loc. 
> > > > > > Should I modify this to check the contents of the loc for equality?
> > > > > > 
> > > > > > - We call `getDeclAtPosition` only looking for 
> > > > > > DeclRelation::TemplatePattern | DeclRelation::Alias, but this is 
> > > > > > actually a DeclRelation::Underlying. If I don't add that we filter 
> > > > > > out the ObjCCategoryImplDecl. If I add it we get a failure in 
> > > > > > LocateSymbol.TemplateTypedef (we now find another symbol, not sure 
> > > > > > what is intended here)
> > > > > > 
> > > > > > 
> > > > > > getDeclAtPosition will call findTarget. Due to the changes above we 
> > > > > > map ObjCCategoryImplDecl to its interface. This is OK but then when 
> > > > > > we check for the loc it's obviously != to the impl's loc. Should I 
> > > > > > modify this to check the contents of the loc for equality?
> > > > > 
> > > > > Oh right... yes, this seems fine to me (for the ObjCContainerDecl 
> > > > > subclasses only, and with a comment) 
> > > > > 
> > > > > > We call getDeclAtPosition only looking for 
> > > > > > DeclRelation::TemplatePattern | DeclRelation::Alias, but this is 
> > > > > > actually a DeclRelation::Underlying. If I don't add that we filter 
> > > > > > out the ObjCCategoryImplDecl. If I add it we get a failure in 
> > > > > > LocateSymbol.TemplateTypedef (we now find another symbol, not sure 
> > > > > > what is intended here)
> > > > > 
> > > > > I'm not sure what "this" in "this is actually a 
> > > > > DeclRelation::Underlying" refers to. Do you have a failing testcase?
> > > > > if the cursor is exactly on the token Ext... are categories 
> > > > > explicitly/separately declared anywhere? I guess not. If they are, we 
> > > > > could special case this too.
> > > > 
> > > > Not besides what was mentioned above, so I think it's OK at the moment.
> > > > 
> > > > > I'm not sure what "this" in "this is actually a 
> > > > > DeclRelation::Underlying" refers to. Do you have a failing testcase?
> > > > 
> > > > I meant that for ObjC, I used `DeclRelation::Underlying` so I have to 
> > > > include it to get the `ObjCCategoryImplDecl`. I guess I can later 
> > > > filter out the `DeclRelation::Underlying` unless it's for the ObjC case.
> > > > 
> > > > Failing test, I think only returning callback is intentional?
> > > > 
> > > > ```
> > > >  LocateSymbol.TemplateTypedefs
> > > > 
> > > > Value of: locateSymbolAt(AST, T.point())
> > > > Expected: has 1 element that sym "callback"
> > > >   Actual: { function: 1:30-1:38@file:///clangd-test/TestTU.cpp 
> > > > def=1:30-1:38@file:///clangd-test/TestTU.cpp, callback: 
> > > > 2:29-2:37@file:///clangd-test/TestTU.cpp }, which has 2 elements
> > > > 
> > > > Code:
> > > >     template <class T> struct function {};
> > > >     template <class T> using callback = function<T()>;
> > > > 
> > > >     c^allback<int> foo;
> > > > ```
> > > > 
> > > > 
> > > > 
> > > > 
> > > > I meant that for ObjC, I used DeclRelation::Underlying
> > > 
> > > `Underlying` isn't appropriate here - it's used for situations like 
> > > typedefs where there's clearly two symbols (two names) and an 
> > > asymmetrical synonym relation (e.g. int32 is a synonym for int, but not 
> > > the other way around).
> > > Here we have a declaration/definition pair of a (what we're treating as) 
> > > a single decl.
> > > 
> > > Can you just stop setting `Underlying` in FindTargets?
> > If I do that it'll be filtered out since it's not a 
> > DeclRelation::TemplatePattern | DeclRelation::Alias. Should I add a new 
> > DeclRelation for this?
> I think one of us is confused about what these bitmasks do :-)
>  - bits set on a particular decl *restrict* when that decl will be considered 
> a target
>  - bits passed to targetDecl() *allow* decls with those bits to be returned
> 
> Not all targets found have a relation set, e.g. a DeclRefExpr to a variable 
> doesn't have any of these bits. This means it's universal - it'll always be 
> considered the target. 
> Bits are basically set when we have to make a choice of whether to return 
> some decl (if we're looking at the std::string type, then the std::string 
> typedef is a target if we want aliases).
Haha yeah, should have just tried it. Didn't realize the masking style in 
`targetDecl` which filters from `allTargetDecls` always includes 0 Relations 
sets (since it's a not a normal filter, it's inverting). It works =)


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