Tolerate target cycles when using dependency inference #10393
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# Rust tests will be skipped. Delete if not intended. [ci skip-rust-tests]
We can now use our conditional `if TYPE_CHECKING` imports. We no longer have the problem that sometimes MyPy would fail to find the import; all dependencies are properly modeled :) # Rust tests will be skipped. Delete if not intended. [ci skip-rust-tests]
stuhood
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Jul 17, 2020
Eric-Arellano
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Jul 18, 2020
…build#10393)" This reverts commit d2ecdda.
Eric-Arellano
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…" (#10401) It's flaky. Sometimes dependencies are not resolved properly: https://travis-ci.com/github/pantsbuild/pants/jobs/362307468#L802 [ci skip-rust-tests]
stuhood
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…in file-addresses. (#10409) ### Problem After more deeply investigating the issues with #10230 (demonstrated in #10393 and its revert), it doesn't seem like the right idea to rely on the engine's cycle detection (which the implementation of #10230 showed should primarily be used for deadlock detection) to expose high level cycle tolerance for the build graph. ### Solution Move to iterative transitive target expansion (à la #10046), and cycle detect afterward using DFS with a stack of visited entries. ### Result Fixes #10059, and closes #10229. A followup will back out portions of #10230 (but not all of it, as there were a number of other improvements mixed in). [ci skip-rust-tests]
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Closes #10059.
It's common in many languages, including Python, to sometimes have import cycles. When using generated subtargets—meaning either dependency inference or explicit file dependencies—Pants will tolerate these cycles. For now, there is no other way to express that a cycle should be tolerated. In the future, we may consider adding a syntax to BUILD files to allow indicating that cycles should be tolerated; it's easier to loosen than it is to tighten.
[ci skip-rust-tests]