cmd/cover: replace code using optimized golang.org/x/tools/cover

After CL 179377, this change deletes all the prior cmd/cover code
and instead vendors and type aliases code using the significantly
optimized  golang.org/x/tools/cover, which sped up ParseProfiles by
manually parsing profiles instead of a regex. The speed up was:

name         old time/op   new time/op   delta
ParseLine-12 2.43µs ± 2%   0.05µs ± 8%   -97.98% (p=0.000 n=10+9)

name         old speed     new speed       delta
ParseLine-12 42.5MB/s ± 2% 2103.2MB/s ± 7% +4853.14% (p=0.000 n=10+9)

Fixes #32211.

Change-Id: Ie4e8be7502f25eb95fae7a9d8334fc97b045d53f
Reviewed-on: https://go-review.googlesource.com/c/go/+/249759
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>

2 files changed, 262 insertions, 0 deletions

diff --git a/src/cmd/vendor/golang.org/x/tools/cover/profile.go b/src/cmd/vendor/golang.org/x/tools/cover/profile.go
new file mode 100644
index 0000000000..57195774ce
--- /dev/null
+++ b/src/cmd/vendor/golang.org/x/tools/cover/profile.go
@@ -0,0 +1,261 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package cover provides support for parsing coverage profiles
+// generated by "go test -coverprofile=cover.out".
+package cover // import "golang.org/x/tools/cover"
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"math"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// Profile represents the profiling data for a specific file.
+type Profile struct {
+	FileName string
+	Mode     string
+	Blocks   []ProfileBlock
+}
+
+// ProfileBlock represents a single block of profiling data.
+type ProfileBlock struct {
+	StartLine, StartCol int
+	EndLine, EndCol     int
+	NumStmt, Count      int
+}
+
+type byFileName []*Profile
+
+func (p byFileName) Len() int           { return len(p) }
+func (p byFileName) Less(i, j int) bool { return p[i].FileName < p[j].FileName }
+func (p byFileName) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
+// ParseProfiles parses profile data in the specified file and returns a
+// Profile for each source file described therein.
+func ParseProfiles(fileName string) ([]*Profile, error) {
+	pf, err := os.Open(fileName)
+	if err != nil {
+		return nil, err
+	}
+	defer pf.Close()
+
+	files := make(map[string]*Profile)
+	buf := bufio.NewReader(pf)
+	// First line is "mode: foo", where foo is "set", "count", or "atomic".
+	// Rest of file is in the format
+	//	encoding/base64/base64.go:34.44,37.40 3 1
+	// where the fields are: name.go:line.column,line.column numberOfStatements count
+	s := bufio.NewScanner(buf)
+	mode := ""
+	for s.Scan() {
+		line := s.Text()
+		if mode == "" {
+			const p = "mode: "
+			if !strings.HasPrefix(line, p) || line == p {
+				return nil, fmt.Errorf("bad mode line: %v", line)
+			}
+			mode = line[len(p):]
+			continue
+		}
+		fn, b, err := parseLine(line)
+		if err != nil {
+			return nil, fmt.Errorf("line %q doesn't match expected format: %v", line, err)
+		}
+		p := files[fn]
+		if p == nil {
+			p = &Profile{
+				FileName: fn,
+				Mode:     mode,
+			}
+			files[fn] = p
+		}
+		p.Blocks = append(p.Blocks, b)
+	}
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
+	for _, p := range files {
+		sort.Sort(blocksByStart(p.Blocks))
+		// Merge samples from the same location.
+		j := 1
+		for i := 1; i < len(p.Blocks); i++ {
+			b := p.Blocks[i]
+			last := p.Blocks[j-1]
+			if b.StartLine == last.StartLine &&
+				b.StartCol == last.StartCol &&
+				b.EndLine == last.EndLine &&
+				b.EndCol == last.EndCol {
+				if b.NumStmt != last.NumStmt {
+					return nil, fmt.Errorf("inconsistent NumStmt: changed from %d to %d", last.NumStmt, b.NumStmt)
+				}
+				if mode == "set" {
+					p.Blocks[j-1].Count |= b.Count
+				} else {
+					p.Blocks[j-1].Count += b.Count
+				}
+				continue
+			}
+			p.Blocks[j] = b
+			j++
+		}
+		p.Blocks = p.Blocks[:j]
+	}
+	// Generate a sorted slice.
+	profiles := make([]*Profile, 0, len(files))
+	for _, profile := range files {
+		profiles = append(profiles, profile)
+	}
+	sort.Sort(byFileName(profiles))
+	return profiles, nil
+}
+
+// parseLine parses a line from a coverage file.
+// It is equivalent to the regex
+// ^(.+):([0-9]+)\.([0-9]+),([0-9]+)\.([0-9]+) ([0-9]+) ([0-9]+)$
+//
+// However, it is much faster: https://golang.org/cl/179377
+func parseLine(l string) (fileName string, block ProfileBlock, err error) {
+	end := len(l)
+
+	b := ProfileBlock{}
+	b.Count, end, err = seekBack(l, ' ', end, "Count")
+	if err != nil {
+		return "", b, err
+	}
+	b.NumStmt, end, err = seekBack(l, ' ', end, "NumStmt")
+	if err != nil {
+		return "", b, err
+	}
+	b.EndCol, end, err = seekBack(l, '.', end, "EndCol")
+	if err != nil {
+		return "", b, err
+	}
+	b.EndLine, end, err = seekBack(l, ',', end, "EndLine")
+	if err != nil {
+		return "", b, err
+	}
+	b.StartCol, end, err = seekBack(l, '.', end, "StartCol")
+	if err != nil {
+		return "", b, err
+	}
+	b.StartLine, end, err = seekBack(l, ':', end, "StartLine")
+	if err != nil {
+		return "", b, err
+	}
+	fn := l[0:end]
+	if fn == "" {
+		return "", b, errors.New("a FileName cannot be blank")
+	}
+	return fn, b, nil
+}
+
+// seekBack searches backwards from end to find sep in l, then returns the
+// value between sep and end as an integer.
+// If seekBack fails, the returned error will reference what.
+func seekBack(l string, sep byte, end int, what string) (value int, nextSep int, err error) {
+	// Since we're seeking backwards and we know only ASCII is legal for these values,
+	// we can ignore the possibility of non-ASCII characters.
+	for start := end - 1; start >= 0; start-- {
+		if l[start] == sep {
+			i, err := strconv.Atoi(l[start+1 : end])
+			if err != nil {
+				return 0, 0, fmt.Errorf("couldn't parse %q: %v", what, err)
+			}
+			if i < 0 {
+				return 0, 0, fmt.Errorf("negative values are not allowed for %s, found %d", what, i)
+			}
+			return i, start, nil
+		}
+	}
+	return 0, 0, fmt.Errorf("couldn't find a %s before %s", string(sep), what)
+}
+
+type blocksByStart []ProfileBlock
+
+func (b blocksByStart) Len() int      { return len(b) }
+func (b blocksByStart) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
+func (b blocksByStart) Less(i, j int) bool {
+	bi, bj := b[i], b[j]
+	return bi.StartLine < bj.StartLine || bi.StartLine == bj.StartLine && bi.StartCol < bj.StartCol
+}
+
+// Boundary represents the position in a source file of the beginning or end of a
+// block as reported by the coverage profile. In HTML mode, it will correspond to
+// the opening or closing of a <span> tag and will be used to colorize the source
+type Boundary struct {
+	Offset int     // Location as a byte offset in the source file.
+	Start  bool    // Is this the start of a block?
+	Count  int     // Event count from the cover profile.
+	Norm   float64 // Count normalized to [0..1].
+	Index  int     // Order in input file.
+}
+
+// Boundaries returns a Profile as a set of Boundary objects within the provided src.
+func (p *Profile) Boundaries(src []byte) (boundaries []Boundary) {
+	// Find maximum count.
+	max := 0
+	for _, b := range p.Blocks {
+		if b.Count > max {
+			max = b.Count
+		}
+	}
+	// Divisor for normalization.
+	divisor := math.Log(float64(max))
+
+	// boundary returns a Boundary, populating the Norm field with a normalized Count.
+	index := 0
+	boundary := func(offset int, start bool, count int) Boundary {
+		b := Boundary{Offset: offset, Start: start, Count: count, Index: index}
+		index++
+		if !start || count == 0 {
+			return b
+		}
+		if max <= 1 {
+			b.Norm = 0.8 // Profile is in"set" mode; we want a heat map. Use cov8 in the CSS.
+		} else if count > 0 {
+			b.Norm = math.Log(float64(count)) / divisor
+		}
+		return b
+	}
+
+	line, col := 1, 2 // TODO: Why is this 2?
+	for si, bi := 0, 0; si < len(src) && bi < len(p.Blocks); {
+		b := p.Blocks[bi]
+		if b.StartLine == line && b.StartCol == col {
+			boundaries = append(boundaries, boundary(si, true, b.Count))
+		}
+		if b.EndLine == line && b.EndCol == col || line > b.EndLine {
+			boundaries = append(boundaries, boundary(si, false, 0))
+			bi++
+			continue // Don't advance through src; maybe the next block starts here.
+		}
+		if src[si] == '\n' {
+			line++
+			col = 0
+		}
+		col++
+		si++
+	}
+	sort.Sort(boundariesByPos(boundaries))
+	return
+}
+
+type boundariesByPos []Boundary
+
+func (b boundariesByPos) Len() int      { return len(b) }
+func (b boundariesByPos) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
+func (b boundariesByPos) Less(i, j int) bool {
+	if b[i].Offset == b[j].Offset {
+		// Boundaries at the same offset should be ordered according to
+		// their original position.
+		return b[i].Index < b[j].Index
+	}
+	return b[i].Offset < b[j].Offset
+}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index af92df8721..7a8e98733a 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -46,6 +46,7 @@ golang.org/x/sys/unix
 golang.org/x/sys/windows
 # golang.org/x/tools v0.1.1-0.20210220032852-2363391a5b2f
 ## explicit
+golang.org/x/tools/cover
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/internal/analysisflags
 golang.org/x/tools/go/analysis/internal/facts