resolving this, discussing below

Perhaps this LogContext can also contain the number of stack frames added by the log stack. This would allow the creation of middleware-like log sinks that delegate to other sinks, while keeping the call stack count correct.

This is what WithCallDepth() is for. I agree that assuming literal 1 in the LogSink is kind of a mess, though. Passing it to every call to Info() feels a bit silly - it's not going to change, like the levels. It almost feels like logr.CallFrameCount() (simple, ugly) or something like:

logr.New(sink) calls sink.Init(numCallFrames), (probably a struct) which can choose to store that info if it needs.

agree

Good point. Early drafts needed this, but not any more.

On compat: There are some things that are just awkward after this, like DiscardLogger (the type) no longer making sense (it's a LogSink). We could jump thru hoops to make things work (make DiscardLogger a struct that embeds a Logger) or we could just make this the one breaking change. MOST clients will be fine with a recompile, and a small number will hit edge cases.

If we do that, we can EOL InfoLogger and a few other things.

Forcing noinline in the benchmark makes it more representative.

Before:

$ GO111MODULE=off go test -bench=. ./benchmark/
goos: linux
goarch: amd64
pkg: github.com/go-logr/logr/benchmark
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkDiscardInfoOneArg-6        	25409384	        54.15 ns/op
BenchmarkDiscardInfoSeveralArgs-6   	 8511532	       146.8 ns/op
BenchmarkDiscardV0Info-6            	 8260953	       152.7 ns/op
BenchmarkDiscardV9Info-6            	 8753974	       147.9 ns/op
BenchmarkDiscardError-6             	 8291468	       146.7 ns/op
BenchmarkDiscardWithValues-6        	18875984	        67.67 ns/op
BenchmarkDiscardWithName-6          	528824234	         2.077 ns/op
BenchmarkFuncrInfoOneArg-6          	 2606715	       476.2 ns/op
BenchmarkFuncrInfoSeveralArgs-6     	  823752	      1302 ns/op
BenchmarkFuncrV0Info-6              	  915470	      1422 ns/op
BenchmarkFuncrV9Info-6              	 4300730	       277.6 ns/op
BenchmarkFuncrError-6               	  837588	      1369 ns/op
BenchmarkFuncrWithValues-6          	 4193628	       294.4 ns/op
BenchmarkFuncrWithName-6            	10532635	       106.4 ns/op

After:

$ GO111MODULE=off go test -bench=. ./benchmark/
goos: linux
goarch: amd64
pkg: github.com/go-logr/logr/benchmark
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkDiscardInfoOneArg-6        	23285353	        52.58 ns/op
BenchmarkDiscardInfoSeveralArgs-6   	 8481985	       146.9 ns/op
BenchmarkDiscardV0Info-6            	 7851495	       144.8 ns/op
BenchmarkDiscardV9Info-6            	 8797778	       144.8 ns/op
BenchmarkDiscardError-6             	 7889066	       148.1 ns/op
BenchmarkDiscardWithValues-6        	19125424	        68.10 ns/op
BenchmarkDiscardWithName-6          	500619270	         2.165 ns/op
BenchmarkFuncrInfoOneArg-6          	 2841159	       490.9 ns/op
BenchmarkFuncrInfoSeveralArgs-6     	  887854	      1266 ns/op
BenchmarkFuncrV0Info-6              	  885891	      1221 ns/op
BenchmarkFuncrV9Info-6              	 7902538	       145.6 ns/op
BenchmarkFuncrError-6               	  852745	      1401 ns/op
BenchmarkFuncrWithValues-6          	 4401705	       295.1 ns/op
BenchmarkFuncrWithName-6            	11857100	       105.0 ns/op

Notably BenchmarkFuncrV9Info was cut almost in half, and there's room for more optimization.

I will make a new push with this change.

Hmm, I think a big part of this is the benchmark benefitting from optimizations that probably are not realistic in the wild. I'll look into it more later

Switching benchmark to Discard():

Before:

BenchmarkInfoOneArg-6        	309439507	         3.628 ns/op
BenchmarkInfoSeveralArgs-6   	103684642	        11.17 ns/op
BenchmarkV0Info-6            	10411196	       115.8 ns/op
BenchmarkV9Info-6            	 9963486	       118.2 ns/op
BenchmarkError-6             	82650194	        12.14 ns/op
BenchmarkWithValues-6        	220570576	         5.585 ns/op
BenchmarkWithName-6          	723292029	         1.441 ns/op

After:

BenchmarkInfoOneArg-6        	28276839	        46.68 ns/op
BenchmarkInfoSeveralArgs-6   	 9974653	       114.4 ns/op
BenchmarkV0Info-6            	11343361	       118.7 ns/op
BenchmarkV9Info-6            	10160247	       117.6 ns/op
BenchmarkError-6             	10033260	       113.5 ns/op
BenchmarkWithValues-6        	21537408	        59.31 ns/op
BenchmarkWithName-6          	502713001	         2.189 ns/op