cmd/dist: require Go 1.17 for building Go

This makes builds using earlier Go bootstrap versions fail pretty clearly:

% GOROOT_BOOTSTRAP=$HOME/sdk/go1.16 ./make.bash
Building Go cmd/dist using /Users/rsc/sdk/go1.16. (go1.16 darwin/amd64)
found packages main (build.go) and building_Go_requires_Go_1_17_or_later (notgo117.go) in /Users/rsc/go/src/cmd/dist
%

All the builders have Go 1.17 or later for bootstrap now except
for the android corellium builders, which still need updating (#54246).
We are accepting breakage on those for now.

Fixes #44505.

Change-Id: I12a67f42f61dba43a331cee0a150194d3e42c044
Reviewed-on: https://go-review.googlesource.com/c/go/+/420902
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/dist/notgo117.go b/src/cmd/dist/notgo117.go
new file mode 100644 (file)
index 0000000..eb1c949
--- /dev/null
+++ b/src/cmd/dist/notgo117.go
@@ -0,0 +1,22 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Go 1.20 and later requires Go 1.17 as the bootstrap toolchain.
+// If cmd/dist is built using an earlier Go version, this file will be
+// included in the build and cause an error like:
+//
+// % GOROOT_BOOTSTRAP=$HOME/sdk/go1.16 ./make.bash
+// Building Go cmd/dist using /Users/rsc/sdk/go1.16. (go1.16 darwin/amd64)
+// found packages main (build.go) and building_Go_requires_Go_1_17_or_later (notgo117.go) in /Users/rsc/go/src/cmd/dist
+// %
+//
+// which is the best we can do under the circumstances.
+//
+// See go.dev/issue/44505 for more background on
+// why Go moved on from Go 1.4 for bootstrap.
+
+//go:build !go1.17
+// +build !go1.17
+
+package building_Go_requires_Go_1_17_or_later