Fix rule graph nondeterminism due to undetected ambiguity #7379
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…dep. Otherwise, we will not detect the case where the same rule can be satisfied by multiple parameter combinations.
…e if it consumes a provided Get param (possibly transitively).
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approved these changes
Mar 14, 2019
| let mut rules_by_kind: HashMap<EntryWithDeps, (usize, &Entry)> = HashMap::new(); | ||
| for satisfiable_entry in &satisfiable_entries { | ||
| // We prefer the non-ambiguous rule with the smallest set of Params, as that minimizes Node | ||
| // identities in the graph and biases toward receiving values from dependencies (which do not |
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This is "identities", which is accurate here... we refer to the Params that a @rule consumes as part of its "identity", because the same @rule can be used with multiple sets of Params, which might each (as seen in this ticket!) affect their behaviour.
blorente
reviewed
Mar 14, 2019
…nested_raise` (because it was not installed).
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Problem
Integration tests of
@console_ruleswould frequently flake (as in #6782) with rules self-cycling in a peculiar way. Investigating the failure lead to the conclusion that theRuleGraphwas being constructed non-deterministically.The source of the non-determinism was that we were "simplifying" all instances of one
@rulethat used the same number ofParams, and treating them interchangeably. But that simplification was subject to rust's randomized hash ordering, and so we would choose which of theParamsto use at random.After fixing that non-determinism, we also needed to solve the underlying ambiguities (there were two or three) that lead to there being multiple options to choose from.
Solution
GraphMaker::choose_dependencyto not simplify rules, and instead preserve all candidates with the current minimumParamset size.Paramprovided by aGetare eligible to satisfy it. See the explanation in the test.Result
Unskips
@console_ruleintegration tests, and adds a (previously flaky, now stable) unit test of the ambiguous case. Fixes #6782.