Modernization Phase 2.2: modules — streamr-logger + streamr-utils (folly GMF, coro canary) [iosbuild]

[ptesavol]

The phase the plan budgeted risk for: folly enters the global module fragment, and streamr-utils is the folly::coro coroutine canary. Both cleared with margin.

What's migrated

• streamr-logger — 4 partitions (:Logger, :LoggerImpl, :SLogger, :StreamrLogLevel) + primary unit. folly's logging machinery compiles in the GMF without incident. detail/ headers get no partitions (internal API); the detail-testing LoggerEnvTest keeps its detail #include alongside import streamr.logger — mixing is the designed property of the façade.
• streamr-utils — 21 partitions + primary. The coroutine canary (waitForEvent, waitForCondition, collect, toCoroTask — folly::coro Tasks in exported signatures) passed with zero compiler workarounds under Clang 22. The per-header opt-out budget went unused.
• 20 test files + both examples now import; logger 63/63, utils 49/49 tests green through modules.

Mechanisms discovered (now part of the scaffolding/docs)

1. target_compile_features(… PUBLIC cxx_std_26) is required on exported module targets — when another build tree consumes the export, CMake synthesizes a BMI-compiling target on the consumer side and hard-errors unless the standard is an exported usage requirement. Added to streamr_add_module_library(); surfaced the moment logger consumed json's export.
2. Namespace-scope constexpr constants have internal linkage and can't be re-exported — 7 header constants became inline constexpr (the correct C++17 idiom regardless of modules).
3. clangd-modules root cause pinned down: the quirks from 2.1 and this phase share one mechanism — clangd fails to unify std types between its preamble and types reached through BMIs, biting only where std types cross the module boundary in import-using files. One test file (toEthereumAddressOrENSNameTest.cpp, whose whole API is std types in Branded wrappers) needed the planned lint-exclusion fallback — first and only use; the compiler still typechecks it on every build. Also: bugprone-exception-escape now correctly fires on main() in import-using files (clangd sees deeper through BMIs) — real findings, fixed with function-try-blocks.

Verification

Gate	Result
Package builds (26 BMIs + archives)	✅
Package tests via import	✅ logger 63/63, utils 49/49
Downstream standalone builds (proto-rpc, dht — find_package + #include)	✅ unchanged
Root tree	✅ 307/307
Full lint	✅ (one documented exclusion)
iOS cross-build	this PR ([iosbuild])

Honest bench note: no incremental-rebuild improvement is expected yet — dht/trackerless-network still #include SLogger/utils headers. The measured win (the 48-TU/62–70 s SLogger.hpp baseline) arrives when those packages flip in 2.4/2.5 and their test TUs load BMIs instead of re-parsing the header stack.

Next

Phase 2.3: streamr-proto-rpc — the first :protos partition (over ProtoRpc.pb.h) and the RpcCommunicator template stack.

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