internal/txtar: bring back to main repo, for tests in std

This used to be cmd/go/internal/txtar,
and then it was moved to golang.org/x/tools/txtar
and revendored from there into cmd/vendor/golang.org/x/tools/txtar.

We have a use for txtar in a new test in the standard library,
which cannot access cmd/vendor. But we also don't really want
to vendor it into the standard library as is, because that would
be the first vendoring of x/tools in std, and it would be better
to keep std separate from x/tools, even for testing.

Instead, since a little copying is better than a little dependency,
just make a copy in internal/txtar. The package does not change.

Having done that, replace the uses in cmd/go so that there's
only one copy in the main repo.

Change-Id: I70b5cc05da3f6ebcc0fd9052ebcb3d369fb57956
Reviewed-on: https://go-review.googlesource.com/c/go/+/384254
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/go/internal/fsys/fsys_test.go

@@ -5,14 +5,13 @@ import (
 	"errors"
 	"fmt"
 	"internal/testenv"
+	"internal/txtar"
 	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"reflect"
 	"testing"
-
-	"golang.org/x/tools/txtar"
 )
 
 // initOverlay resets the overlay state to reflect the config.

src/cmd/go/proxy_test.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"internal/txtar"
 	"io"
 	"io/fs"
 	"log"
@@ -30,7 +31,6 @@ import (
 	"golang.org/x/mod/semver"
 	"golang.org/x/mod/sumdb"
 	"golang.org/x/mod/sumdb/dirhash"
-	"golang.org/x/tools/txtar"
 )
 
 var (

src/cmd/go/script_test.go

@@ -15,6 +15,7 @@ import (
 	"fmt"
 	"go/build"
 	"internal/testenv"
+	"internal/txtar"
 	"io/fs"
 	"os"
 	"os/exec"
@@ -33,8 +34,6 @@ import (
 	"cmd/go/internal/robustio"
 	"cmd/go/internal/work"
 	"cmd/internal/sys"
-
-	"golang.org/x/tools/txtar"
 )
 
 var testSum = flag.String("testsum", "", `may be tidy, listm, or listall. If set, TestScript generates a go.sum file at the beginning of each test and updates test files if they pass.`)

src/cmd/go/testdata/addmod.go

@@ -24,13 +24,12 @@ import (
 	"flag"
 	"fmt"
 	exec "internal/execabs"
+	"internal/txtar"
 	"io/fs"
 	"log"
 	"os"
 	"path/filepath"
 	"strings"
-
-	"golang.org/x/tools/txtar"
 )
 
 func usage() {

src/cmd/go/testdata/savedir.go

@@ -18,14 +18,13 @@ package main
 import (
 	"flag"
 	"fmt"
+	"internal/txtar"
 	"io/fs"
 	"log"
 	"os"
 	"path/filepath"
 	"strings"
 	"unicode/utf8"
-
-	"golang.org/x/tools/txtar"
 )
 
 func usage() {

src/cmd/go/testdata/script/README

@@ -7,7 +7,7 @@ In general script files should have short names: a few words, not whole sentence
 The first word should be the general category of behavior being tested,
 often the name of a go subcommand (list, build, test, ...) or concept (vendor, pattern).
 
-Each script is a text archive (go doc cmd/go/internal/txtar).
+Each script is a text archive (go doc internal/txtar).
 The script begins with an actual command script to run
 followed by the content of zero or more supporting files to
 create in the script's temporary file system before it starts executing.

src/cmd/vendor/modules.txt

@@ -96,7 +96,6 @@ golang.org/x/tools/go/types/typeutil
 golang.org/x/tools/internal/analysisinternal
 golang.org/x/tools/internal/lsp/fuzzy
 golang.org/x/tools/internal/typeparams
-golang.org/x/tools/txtar
 # golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
 ## explicit; go 1.11
 golang.org/x/xerrors

src/go/build/deps_test.go

@@ -553,6 +553,9 @@ var depsRules = `
 
 	FMT, container/heap, math/rand
 	< internal/trace;
+
+	FMT
+	< internal/txtar;
 `
 
 // listStdPkgs returns the same list of packages as "go list std".