Xcode Build Tuner

Implement only approved build optimization changes, verify compilation, and prove the result with the same benchmark contract.

Rules

• Require either checked items in .build-benchmark/optimization-plan.md or an explicit user instruction.
• Apply one logical fix at a time; keep edits reviewable and reversible.
• Re-benchmark after changes and report wall-clock deltas.
• If a speculative change regresses or shows no useful benefit, flag it and recommend revert when appropriate.
• Do not revert recommended build settings only because one noisy benchmark failed to improve.

Fix Types

• Build settings: DEBUG_INFORMATION_FORMAT=dwarf for Debug, SWIFT_COMPILATION_MODE=singlefile, COMPILATION_CACHE_ENABLE_CACHING=YES, EAGER_LINKING=YES, SWIFT_USE_INTEGRATED_DRIVER=YES, ONLY_ACTIVE_ARCH=YES, and cross-target setting alignment. Verify with xcodebuild -showBuildSettings.
• Script phases: declare inputs/outputs, add configuration guards, move long lists to .xcfilelist, and enable dependency analysis when possible.
• Source compilation: add types, break generic/chained expressions, mark non-subclassed classes final, tighten access control, extract huge SwiftUI builders, and add explicit closure return types. Read references/fix-patterns.md for examples.
• SwiftPM graph: split oversized modules, remove upward/circular dependencies, extract interface modules, remove unnecessary @_exported import, align options, and pin branch dependencies to tags or revisions. Confirm tags with git ls-remote --tags; verify with xcodebuild -resolvePackageDependencies.

Workflow

1. Read the approved plan or user instruction.
2. Identify exact files/settings for each approved item.
3. Apply the change.
4. Run a quick build to catch compiler/linker errors.
5. Re-run the original baseline command, usually:

   python3 ../../shared/build-optimization/scripts/benchmark_builds.py \
     --project App.xcodeproj --scheme MyApp --configuration Debug \
     --destination "platform=iOS Simulator,name=<latest available iPhone simulator>,OS=latest" \
     --output-dir .build-benchmark

1. Compare clean, cached clean when present, and incremental medians.

Regression Policy

• Evaluate wall-clock time first; cumulative task time is supporting evidence.
• A slower standard clean build can still be acceptable when cached clean or incremental builds improve.
• Keep best-practice settings even without immediate measurable improvement; they align with current Xcode direction and may compound later.
• For speculative source/script/graph changes, recommend revert if all measured build types regress or if there is no median/cached/incremental benefit.
• Distinguish "outlier reduction only" from true median improvement.

Report

Lead with plain wall-clock impact:

Clean build: X.Xs (was Y.Ys) - Z.Zs faster/slower.
Incremental build: X.Xs (was Y.Ys) - Z.Zs faster/slower.

Then include files changed, status per fix (Kept, Kept (best practice), Reverted, Blocked, No improvement), confidence/noise notes, and any deviation from the approved plan. If task work decreased but wall-clock did not, say that parallel Xcode work hid the improvement.

References

• references/fix-patterns.md
• ../../shared/build-optimization/references/build-settings-best-practices.md
• ../../shared/build-optimization/references/recommendation-format.md