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Ruby: Case barrier guards - #10981
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hmac wants to merge 12 commits into
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hmac
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Oct 26, 2022
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- Ruby: Add basic case string comp barrier guard
- Ruby: Use better names in barrier guard predicates
- Ruby: Add more case barrier guard tests
- Ruby: Add SplatExprCfgNode
- Ruby: Recognise more case barrier guards
- Ruby: Fix barrier guard type
- Ruby: Add placeholder test
- Ruby: Add case barrier to command injection query
- Ruby: Merge case barrier with string const barrier
- Ruby: Add custom barrier guard for cases
- Ruby: Move when clause special-case to shared code
This recognises barriers of the form case foo when "some string literal" foo end where the read of `foo` inside the `when` is guarded by the comparison of `foo` with `"some string literal"`. We don't yet recognise more complex constructs such as case array inclusion.
A previous changed relaxed the signature from ExprCfgNode to AstCfgNode.
Both these barriers are for comparison with a constant string, so it seems cleaner to merge them together.
`when` clauses in case expressions exert control over their corresponding `then` branches, but this is not easily noticeable in the CFG. The individual patterns in the clause have conditional successors, not the `when` node itself. Specifically, this means that in an expression such as case foo when "foo", "bar" foo end the pattern `"bar"` technically does not control the read of `foo` on line 3, because that read is also reachable from the previous pattern `"foo"`. Instead of considering the patterns in isolation, we instead consider the entire `when` clause, provided that all patterns have edges to the `then` node with the same successor. In practice this means we copy the implementation of `DataFlow::BarrierGuard` but use a custom predicate in place of `ConditionBlock.controls`.
This means that we will always treat `when` clauses specially when considering whether one basic block controls another. Provided the special case is correect, I think this is fine to do. It allows us to simplify the case barrier guard by using the parameterized module.
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Nov 3, 2022
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Closing in favour of #11114 |
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