Use go:build directives in generated files.

Build constraints are now inferred from go:build directives rather than +build
directives. +build directives are still emitted in generated files as required
in Go 1.16 and earlier.

Note that go/build/constraint was added in Go 1.16, so gVisor now requires Go
1.16.

PiperOrigin-RevId: 387240779

2 files changed, 9 insertions, 6 deletions

diff --git a/tools/go_generics/go_merge/BUILD b/tools/go_generics/go_merge/BUILD
index 5e0487e93..211e6b3ed 100644
--- a/tools/go_generics/go_merge/BUILD
+++ b/tools/go_generics/go_merge/BUILD
@@ -7,6 +7,6 @@ go_binary(
     srcs = ["main.go"],
     visibility = ["//:sandbox"],
     deps = [
-        "//tools/tags",
+        "//tools/constraintutil",
     ],
 )
diff --git a/tools/go_generics/go_merge/main.go b/tools/go_generics/go_merge/main.go
index 801f2354f..81394ddce 100644
--- a/tools/go_generics/go_merge/main.go
+++ b/tools/go_generics/go_merge/main.go
@@ -25,9 +25,8 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
-	"strings"
 
-	"gvisor.dev/gvisor/tools/tags"
+	"gvisor.dev/gvisor/tools/constraintutil"
 )
 
 var (
@@ -131,6 +130,12 @@ func main() {
 	}
 	f.Decls = newDecls
 
+	// Infer build constraints for the output file.
+	bcexpr, err := constraintutil.CombineFromFiles(flag.Args())
+	if err != nil {
+		fatalf("Failed to read build constraints: %v\n", err)
+	}
+
 	// Write the output file.
 	var buf bytes.Buffer
 	if err := format.Node(&buf, fset, f); err != nil {
@@ -141,9 +146,7 @@ func main() {
 		fatalf("opening output: %v\n", err)
 	}
 	defer outf.Close()
-	if t := tags.Aggregate(flag.Args()); len(t) > 0 {
-		fmt.Fprintf(outf, "%s\n\n", strings.Join(t.Lines(), "\n"))
-	}
+	outf.WriteString(constraintutil.Lines(bcexpr))
 	if _, err := outf.Write(buf.Bytes()); err != nil {
 		fatalf("write: %v\n", err)
 	}