cmd/dist: remove darwin/386, darwin/arm as valid ports

This only removes the ability to build it, and removes it as a
src/buildall.bash target (which uses go tool dist list).

Now:

$ go tool dist list | grep ^darwin
darwin/amd64
darwin/arm64

After this, remaining is removing leftover port--specific code in the
tree.

Updates #37610
Updates #37611

Change-Id: I00f03b2355c2e152f75e57abd3063be243529d2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/226985
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>

Author: bradfitz

src/cmd/api/goapi.go

@@ -60,8 +60,6 @@ var contexts = []*build.Context{
 	{GOOS: "linux", GOARCH: "amd64"},
 	{GOOS: "linux", GOARCH: "arm", CgoEnabled: true},
 	{GOOS: "linux", GOARCH: "arm"},
-	{GOOS: "darwin", GOARCH: "386", CgoEnabled: true},
-	{GOOS: "darwin", GOARCH: "386"},
 	{GOOS: "darwin", GOARCH: "amd64", CgoEnabled: true},
 	{GOOS: "darwin", GOARCH: "amd64"},
 	{GOOS: "windows", GOARCH: "amd64"},
@@ -252,6 +250,13 @@ func featureWithoutContext(f string) string {
 	return spaceParensRx.ReplaceAllString(f, "")
 }
 
+// portRemoved reports whether the given port-specific API feature is
+// okay to no longer exist because its port was removed.
+func portRemoved(feature string) bool {
+	return strings.Contains(feature, "(darwin-386)") ||
+		strings.Contains(feature, "(darwin-386-cgo)")
+}
+
 func compareAPI(w io.Writer, features, required, optional, exception []string, allowAdd bool) (ok bool) {
 	ok = true
 
@@ -279,6 +284,8 @@ func compareAPI(w io.Writer, features, required, optional, exception []string, a
 				// acknowledged by being in the file
 				// "api/except.txt". No need to print them out
 				// here.
+			} else if portRemoved(feature) {
+				// okay.
 			} else if featureSet[featureWithoutContext(feature)] {
 				// okay.
 			} else {

src/cmd/api/goapi_test.go

@@ -140,7 +140,6 @@ func TestCompareAPI(t *testing.T) {
 			name: "contexts reconverging",
 			required: []string{
 				"A",
-				"pkg syscall (darwin-386), type RawSockaddrInet6 struct",
 				"pkg syscall (darwin-amd64), type RawSockaddrInet6 struct",
 			},
 			features: []string{

src/cmd/dist/build.go

@@ -1515,9 +1515,7 @@ func checkNotStale(goBinary string, targets ...string) {
 // by 'go tool dist list'.
 var cgoEnabled = map[string]bool{
 	"aix/ppc64":       true,
-	"darwin/386":      false, // Issue 31751
 	"darwin/amd64":    true,
-	"darwin/arm":      true,
 	"darwin/arm64":    true,
 	"dragonfly/amd64": true,
 	"freebsd/386":     true,

src/cmd/go/go_test.go

@@ -1946,9 +1946,9 @@ func TestGenerateUsesBuildContext(t *testing.T) {
 	tg.grepStdout("linux amd64", "unexpected GOOS/GOARCH combination")
 
 	tg.setenv("GOOS", "darwin")
-	tg.setenv("GOARCH", "386")
+	tg.setenv("GOARCH", "arm64")
 	tg.run("generate", "gen")
-	tg.grepStdout("darwin 386", "unexpected GOOS/GOARCH combination")
+	tg.grepStdout("darwin arm64", "unexpected GOOS/GOARCH combination")
 }
 
 func TestGoEnv(t *testing.T) {