v3.0.0-rc.0: breaking changes

[smn]

Summary

First release candidate for v3.0.0. Lands every breaking change deferred to a major version in CRITICAL_REVIEW.md (Phase 7) plus full removal of the V2 parser/evaluator. Cut as an rc so engage CI can surface migration work before final tag.

Breaking changes

• Context.new/2 no longer normalizes by default. lowercase_keys and coerce_strings both default to false. Variable lookup remains case-insensitive at evaluation time. Pass lowercase_keys: true, coerce_strings: true to restore v2 behavior.
• :skip_context_evaluation? removed. Use coerce_strings: false.
• String literals inside expressions are no longer re-evaluated as templates. Top-level evaluate_as_string!/3 is unchanged. Use Expression.evaluate_template/3 for explicit template resolution inside callback arguments.
• Expression.error/1 removed. Use Expression.error_map/1 for the legacy map shape, or raise Expression.Error.
• = on two DateTimes now compares full DateTime (matches ==). v2 incorrectly compared only the date portion via Date.compare/2.
• Entire V2 parser/evaluator removed. Expression.V2, V2.Parser, V2.Compile, V2.Context, V2.Eval, V2.Callbacks, V2.Callbacks.Standard, V2.Autodoc, V2.Compat are all gone. Static-analysis consumers (engage's Turn.Dsl.Validation / Turn.Dsl.Parser) will need to migrate to V1's AST surface or grow new compile-to-AST capabilities — this is the rc's primary forcing function.
• Benchmarks + benchee dep removed. The benchmark/ directory existed for V1↔V2 comparison; with V2 gone it has no purpose. benchee, deep_merge, statistex removed from mix.lock.

Why an rc

tag-and-discover is the strategy: cut the rc, run engage's full CI against it, address fallout (engage's V2 references in Turn.Dsl.Validation / Turn.Dsl.Parser, the one Expression.error/1 call site in turn/build/callbacks.ex:188), then bump to 3.0.0 final.

Test plan

• mix test — 386 doctests, 235 tests, 0 failures
• mix credo --strict — no issues
• mix format --check-formatted — clean
• mix compile --warnings-as-errors — clean
• Run engage CI against 3.0.0-rc.0 to surface migration work
• Address engage fallout (V2 deps, Expression.error/1 call site)
• Tag 3.0.0 final once rc is green

Files

See CHANGELOG.md for the user-facing changelog and V3_PLAN.md for the implementation plan with consumer-impact notes.

[santiagocardo]

This is great 🔥✨🎉
Happy to try this new version on PROD. I hope this fixes existing bugs, especially the ones related to type coercions 🤞

[santiagocardo]

I believe that at some point should highlight this as a syntax error. Users should use == instead.

[santiagocardo]

@smn, if there are no more references to V2, we can remove this to avoid confusion, no?