all: remove coverageredesign experiment

The coverageredesign experiment was turned on by default by
CL 436236 in September, 2022. We've documented it and people
are using it. This CL removes the ability to turn off the experiment.
This removes some old code that is no longer being executed.

For #51430

Change-Id: I88d4998c8b5ea98eef8145d7ca6ebd96f64fbc2b
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-darwin-amd64-longtest,gotip-linux-arm64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/644997
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>

3 files changed, 24 insertions, 112 deletions

diff --git a/src/testing/cover.go b/src/testing/cover.go
index 6ad43ab9ff..74c97d471e 100644
--- a/src/testing/cover.go
+++ b/src/testing/cover.go
@@ -6,13 +6,6 @@
 
 package testing
 
-import (
-	"fmt"
-	"internal/goexperiment"
-	"os"
-	"sync/atomic"
-)
-
 // CoverBlock records the coverage data for a single basic block.
 // The fields are 1-indexed, as in an editor: The opening line of
 // the file is number 1, for example. Columns are measured
@@ -27,8 +20,6 @@ type CoverBlock struct {
 	Stmts uint16 // Number of statements included in this block.
 }
 
-var cover Cover
-
 // Cover records information about test coverage checking.
 // NOTE: This struct is internal to the testing infrastructure and may change.
 // It is not covered (yet) by the Go 1 compatibility guidelines.
@@ -39,86 +30,8 @@ type Cover struct {
 	CoveredPackages string
 }
 
-// Coverage reports the current code coverage as a fraction in the range [0, 1].
-// If coverage is not enabled, Coverage returns 0.
-//
-// When running a large set of sequential test cases, checking Coverage after each one
-// can be useful for identifying which test cases exercise new code paths.
-// It is not a replacement for the reports generated by 'go test -cover' and
-// 'go tool cover'.
-func Coverage() float64 {
-	if goexperiment.CoverageRedesign {
-		return coverage2()
-	}
-	var n, d int64
-	for _, counters := range cover.Counters {
-		for i := range counters {
-			if atomic.LoadUint32(&counters[i]) > 0 {
-				n++
-			}
-			d++
-		}
-	}
-	if d == 0 {
-		return 0
-	}
-	return float64(n) / float64(d)
-}
-
 // RegisterCover records the coverage data accumulators for the tests.
 // NOTE: This function is internal to the testing infrastructure and may change.
 // It is not covered (yet) by the Go 1 compatibility guidelines.
 func RegisterCover(c Cover) {
-	cover = c
-}
-
-// mustBeNil checks the error and, if present, reports it and exits.
-func mustBeNil(err error) {
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "testing: %s\n", err)
-		os.Exit(2)
-	}
-}
-
-// coverReport reports the coverage percentage and writes a coverage profile if requested.
-func coverReport() {
-	if goexperiment.CoverageRedesign {
-		coverReport2()
-		return
-	}
-	var f *os.File
-	var err error
-	if *coverProfile != "" {
-		f, err = os.Create(toOutputDir(*coverProfile))
-		mustBeNil(err)
-		fmt.Fprintf(f, "mode: %s\n", cover.Mode)
-		defer func() { mustBeNil(f.Close()) }()
-	}
-
-	var active, total int64
-	var count uint32
-	for name, counts := range cover.Counters {
-		blocks := cover.Blocks[name]
-		for i := range counts {
-			stmts := int64(blocks[i].Stmts)
-			total += stmts
-			count = atomic.LoadUint32(&counts[i]) // For -mode=atomic.
-			if count > 0 {
-				active += stmts
-			}
-			if f != nil {
-				_, err := fmt.Fprintf(f, "%s:%d.%d,%d.%d %d %d\n", name,
-					blocks[i].Line0, blocks[i].Col0,
-					blocks[i].Line1, blocks[i].Col1,
-					stmts,
-					count)
-				mustBeNil(err)
-			}
-		}
-	}
-	if total == 0 {
-		fmt.Println("coverage: [no statements]")
-		return
-	}
-	fmt.Printf("coverage: %.1f%% of statements%s\n", 100*float64(active)/float64(total), cover.CoveredPackages)
 }
diff --git a/src/testing/newcover.go b/src/testing/newcover.go
index ad2f622640..5a8d728831 100644
--- a/src/testing/newcover.go
+++ b/src/testing/newcover.go
@@ -8,49 +8,52 @@ package testing
 
 import (
 	"fmt"
-	"internal/goexperiment"
 	"os"
 	_ "unsafe" // for linkname
 )
 
-// cover2 variable stores the current coverage mode and a
+// cover variable stores the current coverage mode and a
 // tear-down function to be called at the end of the testing run.
-var cover2 struct {
+var cover struct {
 	mode        string
 	tearDown    func(coverprofile string, gocoverdir string) (string, error)
 	snapshotcov func() float64
 }
 
-// registerCover2 is invoked during "go test -cover" runs.
+// registerCover is invoked during "go test -cover" runs.
 // It is used to record a 'tear down' function
 // (to be called when the test is complete) and the coverage mode.
-func registerCover2(mode string, tearDown func(coverprofile string, gocoverdir string) (string, error), snapcov func() float64) {
+func registerCover(mode string, tearDown func(coverprofile string, gocoverdir string) (string, error), snapcov func() float64) {
 	if mode == "" {
 		return
 	}
-	cover2.mode = mode
-	cover2.tearDown = tearDown
-	cover2.snapshotcov = snapcov
+	cover.mode = mode
+	cover.tearDown = tearDown
+	cover.snapshotcov = snapcov
 }
 
-// coverReport2 invokes a callback in _testmain.go that will
+// coverReport reports the coverage percentage and
+// writes a coverage profile if requested.
+// This invokes a callback in _testmain.go that will
 // emit coverage data at the point where test execution is complete,
 // for "go test -cover" runs.
-func coverReport2() {
-	if !goexperiment.CoverageRedesign {
-		panic("unexpected")
-	}
-	if errmsg, err := cover2.tearDown(*coverProfile, *gocoverdir); err != nil {
+func coverReport() {
+	if errmsg, err := cover.tearDown(*coverProfile, *gocoverdir); err != nil {
 		fmt.Fprintf(os.Stderr, "%s: %v\n", errmsg, err)
 		os.Exit(2)
 	}
 }
 
-// coverage2 returns a rough "coverage percentage so far"
-// number to support the testing.Coverage() function.
-func coverage2() float64 {
-	if cover2.mode == "" {
+// Coverage reports the current code coverage as a fraction in the range [0, 1].
+// If coverage is not enabled, Coverage returns 0.
+//
+// When running a large set of sequential test cases, checking Coverage after each one
+// can be useful for identifying which test cases exercise new code paths.
+// It is not a replacement for the reports generated by 'go test -cover' and
+// 'go tool cover'.
+func Coverage() float64 {
+	if cover.mode == "" {
 		return 0.0
 	}
-	return cover2.snapshotcov()
+	return cover.snapshotcov()
 }
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 3833bfc84b..2bfa4b6db0 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -403,7 +403,6 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"internal/goexperiment"
 	"internal/race"
 	"io"
 	"math/rand"
@@ -700,10 +699,7 @@ func Testing() bool {
 // values are "set", "count", or "atomic". The return value will be
 // empty if test coverage is not enabled.
 func CoverMode() string {
-	if goexperiment.CoverageRedesign {
-		return cover2.mode
-	}
-	return cover.Mode
+	return cover.mode
 }
 
 // Verbose reports whether the -test.v flag is set.
@@ -2021,7 +2017,7 @@ type testDeps interface {
 // It is not meant to be called directly and is not subject to the Go 1 compatibility document.
 // It may change signature from release to release.
 func MainStart(deps testDeps, tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) *M {
-	registerCover2(deps.InitRuntimeCoverage())
+	registerCover(deps.InitRuntimeCoverage())
 	Init()
 	return &M{
 		deps:        deps,