Add string log formatting witnesses and builder 👷

[p4checo]

Checklist

• I've rebased my changes on top of master
• I've built and run the project to see all new and existing tests pass
• I've followed the Mindera swift style guide
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

Until now, we relied on a custom string-based log format to convert log items into log messages. However, it was quite limited because it only allowed a predefined set of components/formats, evaluated the format string for every log item.

By modeling formatting as witnesses wrapping a closure that can be composed, more flexibility is achieved and items are formatted efficiently by performing a single (composed) closure.

To improve ergonomics, a new result builder was created to allow defining log formatting witnesses with a flexible DSL.

Description

• Create LogItemFormatComponent protocol to model first class types for multiple composable format operations.

• Create Log.ItemFormat namespace, to nest:

  • New LogItemFormatComponent implementations, operators and static helpers for most common operations
  • New Formatting witness and static helpers
  • New Builder result builder

• Update Log.StringLogItemFormatter to only require a Formatting and be instantiated via a Log.ItemFormat.Builder.

• Remove LogLevelFormatters.

• Deprecate Log.Item.testItem in favor of Log.Item.dummy().

• Fix and add relevant UTs.

• Add @inlinable annotations for improved optimization possibilities.

Log item formatting:

"<timestamp> <module>? | <level emoji> <level> | [<thread>/<queue>] <function> | <file>:<line> | <msg>"

Old

let string = "$DHH:mm:ss.SSS$d $O | $C $L | [$T/$Q] $F | $n:$l | $M"

New

@Builder var string: Log.ItemFormat.Formatting<String> {
    Group(separator: " ") {
        Group(separator: " ") {
            Timestamp()
            Module()
        }
        .trimmed() // remove empty space if `nil` module
        "|"
        EmojiLevel()
        Level()
            .uppercased()
            .rightPadded(7) // pad with spaces up to max level name length
        "|"
        Group(prefix: "[", separator: "/", suffix: "]") {
            Thread()
            Queue()
        }
        Function()
        "|"
        Group(separator: ":") {
            File()
            Line()
        }
        "|"
        \.message
    }
}

[codecov]

Codecov Report

Merging #252 (27cbac0) into master (d40bdce) will increase coverage by 0.22%.
The diff coverage is 98.85%.

❗ Current head 27cbac0 differs from pull request most recent head 673fac2. Consider uploading reports for the commit 673fac2 to get more accurate results

@@            Coverage Diff             @@
##           master     #252      +/-   ##
==========================================
+ Coverage   92.02%   92.24%   +0.22%     
==========================================
  Files          99      100       +1     
  Lines        3284     3367      +83     
==========================================
+ Hits         3022     3106      +84     
+ Misses        262      261       -1     

Impacted Files	Coverage Δ
.../ItemFormat/Log+ItemFormat+GenericComponents.swift	96.15% <96.15%> (ø)
...ing/ItemFormat/Log+ItemFormat+ItemComponents.swift	100.00% <100.00%> (ø)
...es/Logging/ItemFormat/Log+ItemFormat.Builder.swift	100.00% <100.00%> (ø)
...Logging/ItemFormat/Log+ItemFormat.Formatting.swift	100.00% <100.00%> (ø)
...ng/ItemFormatters/Log+StringLogItemFormatter.swift	100.00% <100.00%> (+5.55%)	⬆️

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