cmd/compile/internal/syntax: add -skip flag to exclude files from Tes…

…tStdLib

TestStdLib reports parsed lines and lines/s information. To make
it easier to compare apples to apples when making changes in the
std lib, a regular expression provided via the -skip flag filters
files we don't want to process.

Change-Id: I27d9c32032eac4e78581205892e4f26947c91bd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/221600
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/cmd/compile/internal/syntax/parser_test.go

@@ -10,16 +10,20 @@ import (
 	"fmt"
 	"io/ioutil"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 )
 
-var fast = flag.Bool("fast", false, "parse package files in parallel")
-var src_ = flag.String("src", "parser.go", "source file to parse")
-var verify = flag.Bool("verify", false, "verify idempotent printing")
+var (
+	fast   = flag.Bool("fast", false, "parse package files in parallel")
+	verify = flag.Bool("verify", false, "verify idempotent printing")
+	src_   = flag.String("src", "parser.go", "source file to parse")
+	skip   = flag.String("skip", "", "files matching this regular expression are skipped by TestStdLib")
+)
 
 func TestParse(t *testing.T) {
 	ParseFile(*src_, func(err error) { t.Error(err) }, nil, 0)
@@ -30,6 +34,15 @@ func TestStdLib(t *testing.T) {
 		t.Skip("skipping test in short mode")
 	}
 
+	var skipRx *regexp.Regexp
+	if *skip != "" {
+		var err error
+		skipRx, err = regexp.Compile(*skip)
+		if err != nil {
+			t.Fatalf("invalid argument for -skip (%v)", err)
+		}
+	}
+
 	var m1 runtime.MemStats
 	runtime.ReadMemStats(&m1)
 	start := time.Now()
@@ -46,6 +59,12 @@ func TestStdLib(t *testing.T) {
 			runtime.GOROOT(),
 		} {
 			walkDirs(t, dir, func(filename string) {
+				if skipRx != nil && skipRx.MatchString(filename) {
+					// Always report skipped files since regexp
+					// typos can lead to surprising results.
+					fmt.Printf("skipping %s\n", filename)
+					return
+				}
 				if debug {
 					fmt.Printf("parsing %s\n", filename)
 				}