[dev.cc] cmd/dist: write cmd/internal/obj/zbootstrap.go

cmd/internal/obj needs information about the default
values of GOROOT, GOARM, GOEXPERIMENT, Version, and so on.
It cannot ask package runtime, because during bootstrap
package runtime comes from Go 1.4.
So it must have its own copy.

Change-Id: I73d3e75a3d47210b3184a51a810ebb44826b81e5
Reviewed-on: https://go-review.googlesource.com/3140Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

.gitignore

@@ -35,6 +35,7 @@ src/cmd/gc/mkbuiltin1
 src/cmd/gc/opnames.h
 src/cmd/gc/y.output
 src/cmd/go/zdefaultcc.go
+src/cmd/internal/obj/zbootstrap.go
 src/go/doc/headscan
 src/runtime/mkversion
 src/runtime/zaexperiment.h

src/cmd/dist/buildruntime.go

@@ -45,3 +45,31 @@ func mkzexperiment(dir, file string) {
 
 	writefile(out, file, 0)
 }
+
+// mkzbootstrap writes cmd/internal/obj/zbootstrap.go:
+//
+//	package obj
+//
+//	const defaultGOROOT = <goroot>
+//	const defaultGOARM = <goarm>
+//	const defaultGOOS = <goos>
+//	const defaultGOARCH = <goarch>
+//	const version = <version>
+//	const goexperiment = <goexperiment>
+//
+func mkzbootstrap(file string) {
+	out := fmt.Sprintf(
+		"// auto generated by go tool dist\n"+
+			"\n"+
+			"package obj\n"+
+			"\n"+
+			"const defaultGOROOT = `%s`\n"+
+			"const defaultGOARM = `%s`\n"+
+			"const defaultGOOS = `%s`\n"+
+			"const defaultGOARCH = `%s`\n"+
+			"const version = `%s`\n"+
+			"const goexperiment = `%s`\n",
+		goroot_final, goarm, gohostos, gohostarch, goversion, os.Getenv("GOEXPERIMENT"))
+
+	writefile(out, file, 0)
+}

src/cmd/dist/buildtool.go

@@ -38,6 +38,8 @@ func bootstrapBuildTools() {
 	}
 	xprintf("##### Building Go toolchain using %s.\n", goroot_bootstrap)
 
+	mkzbootstrap(pathf("%s/src/cmd/internal/obj/zbootstrap.go", goroot))
+
 	// Use $GOROOT/pkg/bootstrap as the bootstrap workspace root.
 	// We use a subdirectory of $GOROOT/pkg because that's the
 	// space within $GOROOT where we store all generated objects.