testing: benchmarks: -bench: allow filtering subbenchmarks

Pull in testing/match.go verbatim from upstream and use it to filter benchmarks.

TODO: also update testing.go to filter tests similarly.

src/testing/match.go

@@ -5,9 +5,131 @@
 package testing
 
 import (
+	"fmt"
+	"os"
 	"strconv"
+	"strings"
+	"sync"
 )
 
+// matcher sanitizes, uniques, and filters names of subtests and subbenchmarks.
+type matcher struct {
+	filter    []string
+	matchFunc func(pat, str string) (bool, error)
+
+	mu       sync.Mutex
+	subNames map[string]int64
+}
+
+// TODO: fix test_main to avoid race and improve caching, also allowing to
+// eliminate this Mutex.
+var matchMutex sync.Mutex
+
+func newMatcher(matchString func(pat, str string) (bool, error), patterns, name string) *matcher {
+	var filter []string
+	if patterns != "" {
+		filter = splitRegexp(patterns)
+		for i, s := range filter {
+			filter[i] = rewrite(s)
+		}
+		// Verify filters before doing any processing.
+		for i, s := range filter {
+			if _, err := matchString(s, "non-empty"); err != nil {
+				fmt.Fprintf(os.Stderr, "testing: invalid regexp for element %d of %s (%q): %s\n", i, name, s, err)
+				os.Exit(1)
+			}
+		}
+	}
+	return &matcher{
+		filter:    filter,
+		matchFunc: matchString,
+		subNames:  map[string]int64{},
+	}
+}
+
+func (m *matcher) fullName(c *common, subname string) (name string, ok, partial bool) {
+	name = subname
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if c != nil && c.level > 0 {
+		name = m.unique(c.name, rewrite(subname))
+	}
+
+	matchMutex.Lock()
+	defer matchMutex.Unlock()
+
+	// We check the full array of paths each time to allow for the case that
+	// a pattern contains a '/'.
+	elem := strings.Split(name, "/")
+	for i, s := range elem {
+		if i >= len(m.filter) {
+			break
+		}
+		if ok, _ := m.matchFunc(m.filter[i], s); !ok {
+			return name, false, false
+		}
+	}
+	return name, true, len(elem) < len(m.filter)
+}
+
+func splitRegexp(s string) []string {
+	a := make([]string, 0, strings.Count(s, "/"))
+	cs := 0
+	cp := 0
+	for i := 0; i < len(s); {
+		switch s[i] {
+		case '[':
+			cs++
+		case ']':
+			if cs--; cs < 0 { // An unmatched ']' is legal.
+				cs = 0
+			}
+		case '(':
+			if cs == 0 {
+				cp++
+			}
+		case ')':
+			if cs == 0 {
+				cp--
+			}
+		case '\\':
+			i++
+		case '/':
+			if cs == 0 && cp == 0 {
+				a = append(a, s[:i])
+				s = s[i+1:]
+				i = 0
+				continue
+			}
+		}
+		i++
+	}
+	return append(a, s)
+}
+
+// unique creates a unique name for the given parent and subname by affixing it
+// with one or more counts, if necessary.
+func (m *matcher) unique(parent, subname string) string {
+	name := fmt.Sprintf("%s/%s", parent, subname)
+	empty := subname == ""
+	for {
+		next, exists := m.subNames[name]
+		if !empty && !exists {
+			m.subNames[name] = 1 // next count is 1
+			return name
+		}
+		// Name was already used. We increment with the count and append a
+		// string with the count.
+		m.subNames[name] = next + 1
+
+		// Add a count to guarantee uniqueness.
+		name = fmt.Sprintf("%s#%02d", name, next)
+		empty = false
+	}
+}
+
 // rewrite rewrites a subname to having only printable characters and no white
 // space.
 func rewrite(s string) string {