time/tzdata: generate zip constant during cmd/dist

We have a make.bash-time generation capability,
so use it to generate the embedded zip file for time/tzdata.
This is one less file to try to review in CLs like CL 455356.

For #22487.
Fixes #43350.

Change-Id: I2fcd0665fa0b1c830baec5fb4cd714483fea25a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/455357
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Author: rsc

.gitignore

@@ -40,6 +40,7 @@ _testmain.go
 /src/internal/buildcfg/zbootstrap.go
 /src/runtime/internal/sys/zversion.go
 /src/unicode/maketables
+/src/time/tzdata/zzipdata.go
 /test.out
 /test/garbage/*.out
 /test/pass.out

lib/time/update.bash

@@ -48,9 +48,8 @@ fi
 cd zoneinfo
 ../mkzip ../../zoneinfo.zip
 cd ../..
-go generate time/tzdata
 
-files="update.bash zoneinfo.zip ../../src/time/tzdata/zipdata.go"
+files="update.bash zoneinfo.zip"
 modified=true
 if git diff --quiet $files; then
 	modified=false

src/cmd/dist/build.go

@@ -558,6 +558,9 @@ var deptab = []struct {
 	{"go/build", []string{
 		"zcgo.go",
 	}},
+	{"time/tzdata", []string{
+		"zzipdata.go",
+	}},
 }
 
 // depsuffix records the allowed suffixes for source files.
@@ -575,6 +578,7 @@ var gentab = []struct {
 	{"zosarch.go", mkzosarch},
 	{"zversion.go", mkzversion},
 	{"zcgo.go", mkzcgo},
+	{"zzipdata.go", mktzdata},
 
 	// not generated anymore, but delete the file if we see it
 	{"enam.c", nil},
@@ -1346,7 +1350,8 @@ func cmdbootstrap() {
 
 	timelog("build", "go_bootstrap")
 	xprintf("Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.\n")
-	install("runtime") // dependency not visible in sources; also sets up textflag.h
+	install("runtime")     // dependency not visible in sources; also sets up textflag.h
+	install("time/tzdata") // no dependency in sources; creates generated file
 	install("cmd/go")
 	if vflag > 0 {
 		xprintf("\n")

src/cmd/dist/buildgo.go

@@ -124,3 +124,20 @@ func mkzcgo(dir, file string) {
 
 	writefile(buf.String(), file, writeSkipSame)
 }
+
+// mktzdata src/time/tzdata/zzipdata.go:
+//
+//	package tzdata
+//	const zipdata = "PK..."
+func mktzdata(dir, file string) {
+	zip := readfile(filepath.Join(dir, "../../../lib/time/zoneinfo.zip"))
+
+	var buf strings.Builder
+	fmt.Fprintf(&buf, "// Code generated by go tool dist; DO NOT EDIT.\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "package tzdata\n")
+	fmt.Fprintln(&buf)
+	fmt.Fprintf(&buf, "const zipdata = %q\n", zip)
+
+	writefile(buf.String(), file, writeSkipSame)
+}

src/time/tzdata/generate_zipdata.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:generate go run generate_zipdata.go
-
 // Package tzdata provides an embedded copy of the timezone database.
 // If this package is imported anywhere in the program, then if
 // the time package cannot find tzdata files on the system,
@@ -67,6 +65,8 @@ func loadFromEmbeddedTZData(name string) (string, error) {
 		zheader     = 0x04034b50
 	)
 
+	// zipdata is provided by zzipdata.go,
+	// which is generated by cmd/dist during make.bash.
 	z := zipdata
 
 	idx := len(z) - ztailsize