Logger output buffered when piping

[kjcjohnson]

The print function in Swift is fully buffered by default, so when piping gen-ir output, the logger outputs get delayed and, occasionally, split.

Example (gen-ir 0.5.0-alpha)
In a CI script, I want to save off the output of gen-ir into a separate file, as well as see the progress in the console. I call gen-ir in a pipe to do so:

set -o pipefail && gen-ir <build-log> <xcarchive> --project-path <workspace> | tee gen-ir.log

Here, each Running command (clang) XX of YY. Target modules processed: ZZ no longer is printed in real time, until enough are printed to fill the buffer. Occasionally, we'll also see, e.g., Running comm or similar split lines, when the full line doesn't fit inside the IO buffer.

Impact
Makes it more difficult to track the progress of gen-ir. In our case, it takes ~15 minutes to process everything, so it would be nice to have the real-time updates instead of waiting for the buffer to fill, which takes ~30s - ~1min.

Suggested Fix
Flush stdout after printing a log message. Not sure what other ways there are, but adding fflush(__stdoutp) after the print call in StdoutLogHandler.swift did it for me.

gen-ir/Sources/GenIR/StdoutLogHandler.swift

Lines 29 to 43 in e8da32c

	func log(
	level: Logger.Level,
	message: Logger.Message,
	metadata: Logger.Metadata?,
	source: String,
	file: String,
	function: String,
	line: UInt
	) {
	let levelPrefix = prefix(for: level)
	let timestamp = timestamp(for: level)
	let lineInfo = lineInfo(for: level, file: file, function: function, line: line)
	print("\(timestamp)\(lineInfo)\(levelPrefix)\(message)")
	}

[NinjaLikesCheez]

This will be addressed in #62 (https://github.com/veracode/gen-ir/pull/62/files#diff-fb10c82a336be9dc08b5db062c7270903e82bb9865d8e8e4aa1a5924ea469ca3) :)

[bmxav]

This has since been merged and will be available in v0.5.0 which we are planning to get out within the next week.