cmd,log,net,runtime: simplify string prefix and suffix processing

Use the TrimPrefix, TrimSuffix and CutPrefix to simplify the code.

Change-Id: I3e2b271ec0d3f9ce664b830e2b0c21ab47337ed0
GitHub-Last-Rev: 4bd1577d24
GitHub-Pull-Request: golang/go#68629
Reviewed-on: https://go-review.googlesource.com/c/go/+/601675
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/cmd/cgo/out.go

@@ -378,9 +378,7 @@ func dynimport(obj string) {
 		defer f.Close()
 		sym, _ := f.ImportedSymbols()
 		for _, s := range sym {
-			if len(s) > 0 && s[0] == '_' {
+			s = strings.TrimPrefix(s, "_")
-				s = s[1:]
-			}
 			checkImportSymName(s)
 			fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s, s, "")
 		}

src/cmd/compile/internal/types2/resolver.go

@@ -167,10 +167,7 @@ func (check *Checker) importPackage(pos syntax.Pos, path, dir string) *Package {
 			if imp == nil {
 				// create a new fake package
 				// come up with a sensible package name (heuristic)
-				name := path
+				name := strings.TrimSuffix(path, "/")
-				if i := len(name); i > 0 && name[i-1] == '/' {
-					name = name[:i-1]
-				}
 				if i := strings.LastIndex(name, "/"); i >= 0 {
 					name = name[i+1:]
 				}

src/cmd/go/internal/load/pkg.go

@@ -2076,11 +2076,7 @@ func resolveEmbed(pkgdir string, patterns []string) (files []string, pmap map[st
 	for _, pattern = range patterns {
 		pid++
 
-		glob := pattern
+		glob, all := strings.CutPrefix(pattern, "all:")
-		all := strings.HasPrefix(pattern, "all:")
-		if all {
-			glob = pattern[len("all:"):]
-		}
 		// Check pattern is valid for //go:embed.
 		if _, err := pathpkg.Match(glob, ""); err != nil || !validEmbedPattern(glob) {
 			return nil, nil, fmt.Errorf("invalid pattern syntax")

src/cmd/go/internal/work/gc.go

@@ -248,10 +248,7 @@ func (a *Action) trimpath() string {
 	// same situations.
 
 	// Strip the object directory entirely.
-	objdir := a.Objdir
+	objdir := strings.TrimSuffix(a.Objdir, string(filepath.Separator))
-	if len(objdir) > 1 && objdir[len(objdir)-1] == filepath.Separator {
-		objdir = objdir[:len(objdir)-1]
-	}
 	rewrite := ""
 
 	rewriteDir := a.Package.Dir

src/log/slog/logger.go

@@ -5,6 +5,7 @@
 package slog
 
 import (
+	"bytes"
 	"context"
 	"log"
 	loginternal "log/internal"
@@ -96,9 +97,7 @@ func (w *handlerWriter) Write(buf []byte) (int, error) {
 
 	// Remove final newline.
 	origLen := len(buf) // Report that the entire buf was written.
-	if len(buf) > 0 && buf[len(buf)-1] == '\n' {
+	buf = bytes.TrimSuffix(buf, []byte{'\n'})
-		buf = buf[:len(buf)-1]
-	}
 	r := NewRecord(time.Now(), level, string(buf), pc)
 	return origLen, w.h.Handle(context.Background(), r)
 }

src/net/dnsclient_unix.go

@@ -18,6 +18,7 @@ import (
 	"internal/bytealg"
 	"internal/godebug"
 	"internal/itoa"
+	"internal/stringslite"
 	"io"
 	"os"
 	"runtime"
@@ -487,9 +488,7 @@ func avoidDNS(name string) bool {
 	if name == "" {
 		return true
 	}
-	if name[len(name)-1] == '.' {
+	name = stringslite.TrimSuffix(name, ".")
-		name = name[:len(name)-1]
-	}
 	return stringsHasSuffixFold(name, ".onion")
 }
 

src/net/http/cookiejar/jar.go

@@ -500,9 +500,7 @@ func (j *Jar) domainAndType(host, domain string) (string, bool, error) {
 	// From here on: If the cookie is valid, it is a domain cookie (with
 	// the one exception of a public suffix below).
 	// See RFC 6265 section 5.2.3.
-	if domain[0] == '.' {
+	domain = strings.TrimPrefix(domain, ".")
-		domain = domain[1:]
-	}
 
 	if len(domain) == 0 || domain[0] == '.' {
 		// Received either "Domain=." or "Domain=..some.thing",

src/runtime/os_darwin.go

@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"internal/abi"
+	"internal/stringslite"
 	"unsafe"
 )
 
@@ -465,10 +466,7 @@ func sysargs(argc int32, argv **byte) {
 	executablePath = gostringnocopy(argv_index(argv, n+1))
 
 	// strip "executable_path=" prefix if available, it's added after OS X 10.11.
-	const prefix = "executable_path="
+	executablePath = stringslite.TrimPrefix(executablePath, "executable_path=")
-	if len(executablePath) > len(prefix) && executablePath[:len(prefix)] == prefix {
-		executablePath = executablePath[len(prefix):]
-	}
 }
 
 func signalM(mp *m, sig int) {