internal/telemetry: remove the concept of a Tagger

The Tagger interface allowed for specifying a key in a tag list and having the
value be aquired from the context automatically. It was almost never used, and
the alternative (using the key to get the value) is not that much more long
winded, so it was not holding it's own weight from a complexity persective alone
but the performance cost of having to use a list of interface rather than a list
of tags was very large. See the benchstat improvements below for the difference
it makes to both speed and memory usage, especially in the no exporter case.

name                 old time/op    new time/op    delta
Baseline-8              341ns ± 2%     342ns ± 1%     ~     (p=0.139 n=19+18)
LoggingNoExporter-8    2.46µs ± 5%    1.97µs ± 3%  -19.88%  (p=0.000 n=19+20)
Logging-8              13.3µs ± 2%    12.8µs ± 2%   -3.42%  (p=0.000 n=17+20)
LoggingStdlib-8        5.39µs ± 6%    5.34µs ± 3%     ~     (p=0.692 n=20+19)

name                 old alloc/op   new alloc/op   delta
Baseline-8              80.0B ± 0%     80.0B ± 0%     ~     (all equal)
LoggingNoExporter-8      728B ± 0%      440B ± 0%  -39.56%  (p=0.000 n=20+20)
Logging-8              2.75kB ± 0%    2.46kB ± 0%  -10.53%  (p=0.000 n=17+20)
LoggingStdlib-8          568B ± 0%      568B ± 0%     ~     (all equal)

name                 old allocs/op  new allocs/op  delta
Baseline-8               5.00 ± 0%      5.00 ± 0%     ~     (all equal)
LoggingNoExporter-8      32.0 ± 0%      23.0 ± 0%  -28.12%  (p=0.000 n=20+20)
Logging-8                88.0 ± 0%      79.0 ± 0%  -10.23%  (p=0.000 n=20+20)
LoggingStdlib-8          28.0 ± 0%      28.0 ± 0%     ~     (all equal)

Change-Id: Ic203ad0c5de7451348976b999a0d038ac532dc39
Reviewed-on: https://go-review.googlesource.com/c/tools/+/221737
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

internal/lsp/diagnostics.go

@@ -203,7 +203,7 @@ func (s *Server) publishReports(ctx context.Context, snapshot source.Snapshot, r
 			Version:     key.id.Version,
 		}); err != nil {
 			if ctx.Err() == nil {
-				log.Error(ctx, "publishReports: failed to deliver diagnostic", err, telemetry.File)
+				log.Error(ctx, "publishReports: failed to deliver diagnostic", err, telemetry.File.Tag(ctx))
 			}
 			continue
 		}

internal/telemetry/log/log.go

@@ -12,7 +12,6 @@ import (
 
 	"golang.org/x/tools/internal/telemetry"
 	"golang.org/x/tools/internal/telemetry/export"
-	"golang.org/x/tools/internal/telemetry/tag"
 )
 
 type Event telemetry.Event
@@ -27,18 +26,18 @@ func With(ctx context.Context, tags ...telemetry.Tag) {
 
 // Print takes a message and a tag list and combines them into a single tag
 // list before delivering them to the loggers.
-func Print(ctx context.Context, message string, tags ...tag.Tagger) {
+func Print(ctx context.Context, message string, tags ...telemetry.Tag) {
 	export.Log(ctx, telemetry.Event{
 		At:      time.Now(),
 		Message: message,
-		Tags:    tag.Tags(ctx, tags...),
+		Tags:    tags,
 	})
 }
 
 // Error takes a message and a tag list and combines them into a single tag
 // list before delivering them to the loggers. It captures the error in the
 // delivered event.
-func Error(ctx context.Context, message string, err error, tags ...tag.Tagger) {
+func Error(ctx context.Context, message string, err error, tags ...telemetry.Tag) {
 	if err == nil {
 		err = errorString(message)
 		message = ""
@@ -47,7 +46,7 @@ func Error(ctx context.Context, message string, err error, tags ...tag.Tagger) {
 		At:      time.Now(),
 		Message: message,
 		Error:   err,
-		Tags:    tag.Tags(ctx, tags...),
+		Tags:    tags,
 	})
 }
 

internal/telemetry/tag.go

@@ -5,7 +5,6 @@
 package telemetry
 
 import (
-	"context"
 	"fmt"
 )
 
@@ -26,12 +25,6 @@ func (t Tag) Format(f fmt.State, r rune) {
 	fmt.Fprintf(f, `%v="%v"`, t.Key, t.Value)
 }
 
-// Tag returns the tag unmodified.
-// It makes Key conform to the Tagger interface.
-func (t Tag) Tag(ctx context.Context) Tag {
-	return t
-}
-
 // Get will get a single key's value from the list.
 func (l TagList) Get(k interface{}) interface{} {
 	for _, t := range l {

internal/telemetry/tag/tag.go

@@ -18,14 +18,6 @@ import (
 //TODO: Do we need to do something more efficient than just store tags
 //TODO: directly on the context?
 
-// Tagger is the interface to something that returns a Tag given a context.
-// Both Tag itself and Key support this interface, allowing methods that can
-// take either (and other implementations as well)
-type Tagger interface {
-	// Tag returns a Tag potentially using information from the Context.
-	Tag(context.Context) telemetry.Tag
-}
-
 // With is roughly equivalent to context.WithValue except that it also notifies
 // registered observers.
 // Unlike WithValue, it takes a list of tags so that you can set many values
@@ -48,12 +40,3 @@ func Get(ctx context.Context, keys ...interface{}) telemetry.TagList {
 	}
 	return tags
 }
-
-// Tags collects a list of tags for the taggers from the context.
-func Tags(ctx context.Context, taggers ...Tagger) telemetry.TagList {
-	tags := make(telemetry.TagList, len(taggers))
-	for i, t := range taggers {
-		tags[i] = t.Tag(ctx)
-	}
-	return tags
-}