refactor(bootstrapper): replace recursion with trampoline for iterative execution

[rd4398]

This commit converts recursive bootstrap methods to generators using the trampoline library, eliminating Python's recursion depth limit for deep/wide dependency graphs.

trampoline source: https://gitlab.com/ferreum/trampoline

Closes: #1068

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: 0f6092c2-3685-45dd-adaa-011f15cbe780

📥 Commits

Reviewing files that changed from the base of the PR and between c2f6fb6 and 1f7ac06.

📒 Files selected for processing (3)

• pyproject.toml
• src/fromager/bootstrapper.py
• tests/test_bootstrapper.py

🚧 Files skipped from review as they are similar to previous changes (2)

• pyproject.toml
• src/fromager/bootstrapper.py

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📝 Walkthrough

Walkthrough

The bootstrap flow was converted from direct recursive calls to a generator-based, trampoline-driven model. bootstrap() now invokes self._bootstrap_gen(...) via trampoline(). Methods _bootstrap_gen, _bootstrap_single_version, _bootstrap_impl, _prepare_build_dependencies, _handle_build_requirements, and _build_from_source were changed to yield work and return generator types; call sites were updated to yield those generators. _get_version_from_package_metadata() now runs _prepare_build_dependencies() through trampoline(). pyproject.toml adds trampoline to dependencies and mypy overrides. Tests were adapted to run generators via trampoline() and to use generator-style mocks.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: converting recursive bootstrap methods to use the trampoline library for iterative execution.
Description check	✅ Passed	The description is related to the changeset, explaining the conversion to generators using trampoline to eliminate recursion depth limits.
Linked Issues check	✅ Passed	The PR addresses issue #1068 by converting recursive bootstrap methods to iterative execution using trampoline, eliminating recursion depth limits for deep dependency graphs.
Out of Scope Changes check	✅ Passed	All changes are scoped to the bootstrap refactoring: adding trampoline dependency, converting methods to generators, and updating tests to use trampoline.

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[dhellmann]

I have to admit, this is a small clean change but I really had to study the trampoline code to make sense of how it works. I'm not sure how I feel about hiding the cleverness in another library vs. having a non-recursive depth-first traversal algorithm here in fromager.

[dhellmann]

Maybe we could be more specific with types here, instead of using typing.Any?

[rd4398]

I think we cannot be more specific because of the way the way trampoline works

- YieldType — we yield child generators, but each yield site yields a different generator type, so a single precise type isn't possible within one method 
                                                                 
- SendType — the value received from yield depends on which child generator was yielded (e.g., SourceBuildResult from _build_from_source, None from _bootstrap_gen)

[dhellmann]

We can still declare our type accurately, even if trampoline doesn't care, can't we?

[rd4398]

I have to admit, this is a small clean change but I really had to study the trampoline code to make sense of how it works. I'm not sure how I feel about hiding the cleverness in another library vs. having a non-recursive depth-first traversal algorithm here in fromager.

Yeah, I agree. I wonder whether we want to move back to implementing our plan for iterative bootstrap even though it is a significantly big change. @LalatenduMohanty what do you think? cc @tiran

[dhellmann]

I have to admit, this is a small clean change but I really had to study the trampoline code to make sense of how it works. I'm not sure how I feel about hiding the cleverness in another library vs. having a non-recursive depth-first traversal algorithm here in fromager.

Yeah, I agree. I wonder whether we want to move back to implementing our plan for iterative bootstrap even though it is a significantly big change. @LalatenduMohanty what do you think? cc @tiran

I'd be interested in seeing the change to compare them for readability.

[rd4398]

I have to admit, this is a small clean change but I really had to study the trampoline code to make sense of how it works. I'm not sure how I feel about hiding the cleverness in another library vs. having a non-recursive depth-first traversal algorithm here in fromager.

Yeah, I agree. I wonder whether we want to move back to implementing our plan for iterative bootstrap even though it is a significantly big change. @LalatenduMohanty what do you think? cc @tiran

I'd be interested in seeing the change to compare them for readability.

Ack, will submit the PR today with that implementation.

[rd4398]

I have to admit, this is a small clean change but I really had to study the trampoline code to make sense of how it works. I'm not sure how I feel about hiding the cleverness in another library vs. having a non-recursive depth-first traversal algorithm here in fromager.

Yeah, I agree. I wonder whether we want to move back to implementing our plan for iterative bootstrap even though it is a significantly big change. @LalatenduMohanty what do you think? cc @tiran

I'd be interested in seeing the change to compare them for readability.

Ack, will submit the PR today with that implementation.

Done. @dhellmann @LalatenduMohanty #1116 is the alternative implementation. Please take a look when you have time