From ec095f1df0ff1b2937205e17b3c011f31d3737ca Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 13 Jul 2020 22:24:52 -0400
Subject: [PATCH] path: avoid import of strings

Pushing path lower in the hierarchy, to allow path < io/fs < os
in the io/fs prototype. But this change is worth doing even if io/fs
is not accepted.

Change-Id: Id51b3a638167ca005dadfb9b730287e518ec12a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/243904
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
---
 src/go/build/deps_test.go |  7 ++++++-
 src/path/match.go         |  4 ++--
 src/path/match_test.go    |  7 +++++--
 src/path/path.go          | 36 ++++++++++++++++++++++++++----------
 src/path/path_test.go     |  3 ++-
 5 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 1edd96c5e3..79836c0d67 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -101,6 +101,11 @@ var depsRules = `
 
 	reflect !< sort;
 
+	RUNTIME, unicode/utf8
+	< path;
+
+	unicode !< path;
+
 	# SYSCALL is RUNTIME plus the packages necessary for basic system calls.
 	RUNTIME, unicode/utf8, unicode/utf16
 	< internal/syscall/windows/sysdll, syscall/js
@@ -137,7 +142,7 @@ var depsRules = `
 	# STR is basic string and buffer manipulation.
 	RUNTIME, io, unicode/utf8, unicode/utf16, unicode
 	< bytes, strings
-	< bufio, path;
+	< bufio;
 
 	bufio, path, strconv
 	< STR;
diff --git a/src/path/match.go b/src/path/match.go
index d39d24450a..837eb8bb8b 100644
--- a/src/path/match.go
+++ b/src/path/match.go
@@ -6,7 +6,7 @@ package path
 
 import (
 	"errors"
-	"strings"
+	"internal/bytealg"
 	"unicode/utf8"
 )
 
@@ -43,7 +43,7 @@ Pattern:
 		star, chunk, pattern = scanChunk(pattern)
 		if star && chunk == "" {
 			// Trailing * matches rest of string unless it has a /.
-			return !strings.Contains(name, "/"), nil
+			return bytealg.IndexByteString(name, '/') < 0, nil
 		}
 		// Look for match at current position.
 		t, ok, err := matchChunk(chunk, name)
diff --git a/src/path/match_test.go b/src/path/match_test.go
index 127180e570..3e027e1f68 100644
--- a/src/path/match_test.go
+++ b/src/path/match_test.go
@@ -2,9 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package path
+package path_test
 
-import "testing"
+import (
+	. "path"
+	"testing"
+)
 
 type MatchTest struct {
 	pattern, s string
diff --git a/src/path/path.go b/src/path/path.go
index c513114b4d..f1f3499f63 100644
--- a/src/path/path.go
+++ b/src/path/path.go
@@ -11,10 +11,6 @@
 // operating system paths, use the path/filepath package.
 package path
 
-import (
-	"strings"
-)
-
 // A lazybuf is a lazily constructed path buffer.
 // It supports append, reading previously appended bytes,
 // and retrieving the final string. It does not allocate a buffer
@@ -139,13 +135,22 @@ func Clean(path string) string {
 	return out.string()
 }
 
+// lastSlash(s) is strings.LastIndex(s, "/") but we can't import strings.
+func lastSlash(s string) int {
+	i := len(s) - 1
+	for i >= 0 && s[i] != '/' {
+		i--
+	}
+	return i
+}
+
 // Split splits path immediately following the final slash,
 // separating it into a directory and file name component.
 // If there is no slash in path, Split returns an empty dir and
 // file set to path.
 // The returned values have the property that path = dir+file.
 func Split(path string) (dir, file string) {
-	i := strings.LastIndex(path, "/")
+	i := lastSlash(path)
 	return path[:i+1], path[i+1:]
 }
 
@@ -155,12 +160,23 @@ func Split(path string) (dir, file string) {
 // empty or all its elements are empty, Join returns
 // an empty string.
 func Join(elem ...string) string {
-	for i, e := range elem {
-		if e != "" {
-			return Clean(strings.Join(elem[i:], "/"))
+	size := 0
+	for _, e := range elem {
+		size += len(e)
+	}
+	if size == 0 {
+		return ""
+	}
+	buf := make([]byte, 0, size+len(elem)-1)
+	for _, e := range elem {
+		if len(buf) > 0 || e != "" {
+			if len(buf) > 0 {
+				buf = append(buf, '/')
+			}
+			buf = append(buf, e...)
 		}
 	}
-	return ""
+	return Clean(string(buf))
 }
 
 // Ext returns the file name extension used by path.
@@ -189,7 +205,7 @@ func Base(path string) string {
 		path = path[0 : len(path)-1]
 	}
 	// Find the last element
-	if i := strings.LastIndex(path, "/"); i >= 0 {
+	if i := lastSlash(path); i >= 0 {
 		path = path[i+1:]
 	}
 	// If empty now, it had only slashes.
diff --git a/src/path/path_test.go b/src/path/path_test.go
index 2a3635300e..a57286f6b8 100644
--- a/src/path/path_test.go
+++ b/src/path/path_test.go
@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package path
+package path_test
 
 import (
+	. "path"
 	"runtime"
 	"testing"
 )
-- 
2.48.1