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Add withMetadata() convenience function for adding multiple metadata k/v pairs to a Logger #322

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14 changes: 14 additions & 0 deletions Sources/Logging/Logging.swift
Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,20 @@ extension Logger {
}
}

/// Convenience function for merging multiple metadata items into a Logger's existing metadata.
///
/// - parameters:
/// - metadata: The metadata to merge into a Logger's existing metadata.
///
/// - note: Logging metadata behaves as a value that means a change to the logging metadata will only affect the
/// very `Logger` it was changed on.
@inlinable
public mutating func mergeMetadata(_ metadata: Logger.Metadata) {
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Can we add the uniquingKeysWith parameter as well à la Dictionary?

metadata.forEach { (key, value) in
self.handler[metadataKey: key] = value
}
Comment on lines +178 to +180
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I suspect in many (all?) handler implementations this will acquire and release a lock for each value we update. Can we call merge directly on the handler.metadata to avoid this? i.e. self.handler.metadata.merge(metadata)

}

/// Get or set the log level configured for this `Logger`.
///
/// - note: `Logger`s treat `logLevel` as a value. This means that a change in `logLevel` will only affect this
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53 changes: 53 additions & 0 deletions Tests/LoggingTests/LoggingTest.swift
Original file line number Diff line number Diff line change
Expand Up @@ -357,6 +357,59 @@ class LoggingTest: XCTestCase {
"nested-list": ["l1str", ["l2str1", "l2str2"]]])
}

func testMergeMetadata() {
let testLogging = TestLogging()
LoggingSystem.bootstrapInternal { testLogging.make(label: $0) }

var logger = Logger(label: "\(#function)")
let metadata: Logger.Metadata = [
"foo": ["bar", "buz"],
"empty-list": [],
"nested-list": ["l1str", ["l2str1", "l2str2"]],
]
logger.mergeMetadata(metadata)
logger.info("first log")
testLogging.history.assertExist(level: .info,
message: "first log",
metadata: ["foo": ["bar", "buz"],
"empty-list": [],
"nested-list": ["l1str", ["l2str1", "l2str2"]]])

// Non-overlapping metadata key-value pairs should be added without affecting existing metadata,
// while overlapping metadata key-value pairs should update the existing key's value.
logger.mergeMetadata([
"foo": ["bar"], // drops "buz" for existing key value
"newkey": "newvalue1" // adds new key-value pair
])
logger.info("second log")
testLogging.history.assertExist(level: .info,
message: "second log",
metadata: ["foo": ["bar"],
"empty-list": [],
"nested-list": ["l1str", ["l2str1", "l2str2"]],
"newkey": "newvalue1"])

// Finally, if new metadata with overlapping keys is added more than once, the
// latest value should be the one set in the Logger metadata.
logger.mergeMetadata([
"foo": [],
"newkey": "newvalue2"
])
logger.mergeMetadata([
"foo": "a new type for this value",
"newkey": "newvalue3"
])
logger.info("third log")
testLogging.history.assertExist(level: .info,
message: "third log",
metadata: ["foo": "a new type for this value",
"empty-list": [],
"nested-list": ["l1str", ["l2str1", "l2str2"]],
"newkey": "newvalue3"])


}

// Example of custom "box" which may be used to implement "render at most once" semantics
// Not thread-safe, thus should not be shared across threads.
internal final class LazyMetadataBox: CustomStringConvertible {
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