[plugin] Line-buffer stdout in the plugin helper so output streams as produced#682
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On Glibc/Musl, stdout is an `extern FILE *` global var, which Swift 6 strict concurrency rejects as "not concurrency-safe" when passed to setvbuf. Import the platform libc with @preconcurrency to suppress the diagnostic for that symbol. Verified with `swift build --target AWSLambdaPluginHelper` in the swiftlang/swift:nightly-6.4.x-bookworm container. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Motivation
When running the SwiftPM plugins (
lambda-init,lambda-build,lambda-deploy), output from thedeploy/deletecommands — and the helper's--helptext — only appeared on screen once the command had finished, instead of streaming as it was produced.The cause is stdio buffering. SwiftPM runs plugins with stdout connected to a pipe rather than a TTY, so the C runtime block-buffers stdout. The three plugins (
AWSLambdaInitializer,AWSLambdaBuilder,AWSLambdaDeployer) print nothing themselves — each is a thin wrapper that spawns the sharedAWSLambdaPluginHelperexecutable and lets it inherit stdout. All user-facingprint()output therefore originates from that one helper process, where it sat in the block buffer until exit.Change
Force line buffering at the start of
AWSLambdaPluginHelper.main():This makes each printed line flush on its newline, so output streams live. Because all three commands funnel through this single entry point, one call covers
init,build,deploy,delete, and the help text — no per-call-site changes and no risk of missing futureprintcalls.The platform libc import block follows the existing pattern in
Sources/AWSLambdaRuntime/Lambda.swift.Scope
AWSLambdaPackager) and the#if swift(<6.4)PluginUtils.swiftpath are intentionally left untouched — their output already streams as produced.Testing
swift build --target AWSLambdaPluginHelpersucceeds.🤖 Generated with Claude Code