Consider reducing redundancy between declaration and references

Consider the following C++ code:

void foo(); // R1
void foo(); // R2

where R1 and R2 indicate two distinct Range vertices.

Following the current LSIF spec, the output should contain the following vertices:

1. Range for R1
2. Range for R2
3. ResultSet
4. DeclarationResult
5. ReferenceResult

and the following edges:

a) 1 -> 3; refersTo
b) 2 -> 3; refersTo
c) 3 -> 4; textDocument/declaration
d) 3 -> 5; textDocument/references
e) 5 -> 1; item (property=declaration)
f) 5 -> 2; item (property=declaration)
g) 4 -> 1
h) 4 -> 2

Note that "e" and "f" could be implicit edges (inlined into array), and "g" and "h" in the current spec are implicit edges (formed by the result field array in DeclarationResult), but that does not affect the crux of the issues.

The crux is that "e" is redundant with "g", and "f" is redundant with "h", and such redundancy would be repeated for every additional declaration in the source code.

Similar redundancy would be present for DefinitionResult and item (property=definition), although on much smaller scale (in general, there is only one definition for a given ResultSet).

I propose that declaration and definition edges going out of ReferenceResult are dropped. They can easily be reconstructed for serving textDocument/references query by augmenting that result set with the results from textDocument/declaration and textDocument/definition from the same ResultSet. Note also that after dropping these edges, "property" field on the "item" edge will no longer be necessary, since "reference" and "referenceResult" could be distinguished by the type of the incoming vertex of the "item" edge.

Are there languages that would make the above not possible?

Start with the LSIF declaration, reference, definition, ResultSet, and item relationships described in issue #25. Determine whether declaration and definition edges can be removed without losing information across languages, then document the decision and any required specification changes; the payload names no files or tests.