go/build: trim filename extension starting at the final dot

Previously, goodOSArchFile trimmed the file name's extension from the first
instance of "." in the name. This resulted in strange behavior when
compiling files with dots in their names.

This change causes goodOSArchFile to trim the file name's extension from
the final instance of ".", as path.Ext suggests should happen.

Fixes golang#46662

Author: knusbaum

src/cmd/vendor/golang.org/x/sys/unix/syscall_darwin.1_12.go renamed to src/cmd/vendor/golang.org/x/sys/unix/syscall_go1_12_darwin.go

@@ -1944,7 +1944,7 @@ func (ctxt *Context) matchTag(name string, allTags map[string]bool) bool {
 // if GOOS=illumos, then files with GOOS=solaris are also matched.
 // if GOOS=ios, then files with GOOS=darwin are also matched.
 func (ctxt *Context) goodOSArchFile(name string, allTags map[string]bool) bool {
-	if dot := strings.Index(name, "."); dot != -1 {
+	if dot := strings.LastIndex(name, "."); dot != -1 {
 		name = name[:dot]
 	}
 

src/cmd/vendor/golang.org/x/sys/unix/syscall_darwin.1_13.go renamed to src/cmd/vendor/golang.org/x/sys/unix/syscall_go1_13_darwin.go

@@ -396,6 +396,8 @@ var matchFileTests = []struct {
 	{ctxtP9, "foo.go", "", true},
 	{ctxtP9, "foo1.go", "// +build linux\n\npackage main\n", false},
 	{ctxtP9, "foo.badsuffix", "", false},
+	{ctxtP9, "file.name_plan9.go", "", true},
+	{ctxtP9, "file.name_linux.go", "", false},
 	{ctxtAndroid, "foo_linux.go", "", true},
 	{ctxtAndroid, "foo_android.go", "", true},
 	{ctxtAndroid, "foo_plan9.go", "", false},
@@ -404,24 +406,29 @@ var matchFileTests = []struct {
 	{ctxtAndroid, "plan9_test.go", "", true},
 	{ctxtAndroid, "arm.s", "", true},
 	{ctxtAndroid, "amd64.s", "", true},
+	{ctxtAndroid, "file.name_android.go", "", true},
+	{ctxtAndroid, "file.name_linux.go", "", true},
+	{ctxtAndroid, "file.name_plan9.go", "", false},
 }
 
 func TestMatchFile(t *testing.T) {
 	for _, tt := range matchFileTests {
-		ctxt := tt.ctxt
-		ctxt.OpenFile = func(path string) (r io.ReadCloser, err error) {
-			if path != "x+"+tt.name {
-				t.Fatalf("OpenFile asked for %q, expected %q", path, "x+"+tt.name)
+		t.Run("", func(t *testing.T) {
+			ctxt := tt.ctxt
+			ctxt.OpenFile = func(path string) (r io.ReadCloser, err error) {
+				if path != "x+"+tt.name {
+					t.Fatalf("OpenFile asked for %q, expected %q", path, "x+"+tt.name)
+				}
+				return &readNopCloser{strings.NewReader(tt.data)}, nil
 			}
-			return &readNopCloser{strings.NewReader(tt.data)}, nil
-		}
-		ctxt.JoinPath = func(elem ...string) string {
-			return strings.Join(elem, "+")
-		}
-		match, err := ctxt.MatchFile("x", tt.name)
-		if match != tt.match || err != nil {
-			t.Fatalf("MatchFile(%q) = %v, %v, want %v, nil", tt.name, match, err, tt.match)
-		}
+			ctxt.JoinPath = func(elem ...string) string {
+				return strings.Join(elem, "+")
+			}
+			match, err := ctxt.MatchFile("x", tt.name)
+			if match != tt.match || err != nil {
+				t.Fatalf("MatchFile(%q) = %v, %v, want %v, nil", tt.name, match, err, tt.match)
+			}
+		})
 	}
 }
 

src/cmd/vendor/golang.org/x/sys/unix/zsyscall_darwin_amd64.1_13.go renamed to src/cmd/vendor/golang.org/x/sys/unix/zsyscall_go1_13_darwin_amd64.go

@@ -51,6 +51,8 @@ var tests = []GoodFileTest{
 	{"file_foo_" + otherArch + ".go", false},
 	{"file_" + thisOS + ".c", true},
 	{"file_" + otherOS + ".c", false},
+	{"file.name_" + thisOS + ".go", true},
+	{"file.name_" + otherOS + ".go", false},
 }
 
 func TestGoodOSArch(t *testing.T) {