Fix generic witness table SequentialIDDecorations #6129
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juliusikkala
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Fixes (hopefully) #5407, although I couldn't get OPs code compiling with the current master branch version of Slang. At least this PR fixes the two similar cases from the comments. This is likely not the correct way to do it, but it's probably easiest to discuss this in a PR since I want to fix this in any case.
The problem appears to be that witness tables for generic structs don't get
SequentialIDDecorations. This is becauseensureWitnessTableSequentialIDschecks for LinkageDecoration, which those generic witness tables don't have (but should they?). WhenaddLinkageDecorationis called for witness tables invisitInheritanceDecl(slang-lower-to-ir.cpp), it starts by finding the outermost generic and attaches the decoration to that, which in this case is not the witness table itself.I tried adding a new flag to
addLinkageDecorationto skip that outermost-generic-search, skipping it only invisitInheritanceDecl, but that broke some tests, so it's probably not that simple.So the overkill approach in this PR is to give
SequentialIDDecorationto every single witness table for whichensureWitnessTableSequentialIDsis called. It doesn't seem to break any tests and fixes the code examples from that issue, but I guess there must be some negative consequences since clearly some effort was seen to only add the IDs in a very specific corner case.