printer: constraints formatting (#209)

Uses `buildtag.Format` to format constraints in the assembly and stub file
printers. This will ensure `// + build` and `//go:build` syntax are used
consistent with the current Go version.

Updates #183

printer/goasm.go

@@ -4,6 +4,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/internal/prnt"
 	"github.com/mmcloughlin/avo/ir"
 	"github.com/mmcloughlin/avo/operand"
@@ -44,8 +45,12 @@ func (p *goasm) header(f *ir.File) {
 	p.Comment(p.cfg.GeneratedWarning())
 
 	if len(f.Constraints) > 0 {
+		constraints, err := buildtags.Format(f.Constraints)
+		if err != nil {
+			p.AddError(err)
+		}
 		p.NL()
-		p.Printf(f.Constraints.GoString())
+		p.Printf(constraints)
 	}
 
 	if len(f.Includes) > 0 {

printer/goasm_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/mmcloughlin/avo/attr"
 	"github.com/mmcloughlin/avo/build"
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/printer"
 	"github.com/mmcloughlin/avo/reg"
 )
@@ -73,13 +74,24 @@ func TestConstraints(t *testing.T) {
 	ctx.ConstraintExpr("linux,386 darwin,!cgo")
 	ctx.ConstraintExpr("!noasm")
 
-	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+	expect := []string{
 		"// Code generated by avo. DO NOT EDIT.",
 		"",
-		"// +build linux,386 darwin,!cgo",
-		"// +build !noasm",
-		"",
-	})
+	}
+	if buildtags.GoBuildSyntaxSupported() {
+		expect = append(expect,
+			"//go:build ((linux && 386) || (darwin && !cgo)) && !noasm",
+		)
+	}
+	if buildtags.PlusBuildSyntaxSupported() {
+		expect = append(expect,
+			"// +build linux,386 darwin,!cgo",
+			"// +build !noasm",
+		)
+	}
+	expect = append(expect, "")
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, expect)
 }
 
 func TestAlignmentNoOperands(t *testing.T) {

printer/stubs.go

@@ -1,6 +1,7 @@
 package printer
 
 import (
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/internal/prnt"
 	"github.com/mmcloughlin/avo/ir"
 )
@@ -19,8 +20,12 @@ func (s *stubs) Print(f *ir.File) ([]byte, error) {
 	s.Comment(s.cfg.GeneratedWarning())
 
 	if len(f.Constraints) > 0 {
+		constraints, err := buildtags.Format(f.Constraints)
+		if err != nil {
+			s.AddError(err)
+		}
 		s.NL()
-		s.Printf(f.Constraints.GoString())
+		s.Printf(constraints)
 	}
 
 	s.NL()

printer/stubs_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/mmcloughlin/avo/build"
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/printer"
 )
 
@@ -26,3 +27,32 @@ func TestStubsPragmas(t *testing.T) {
 		"",
 	})
 }
+
+func TestStubsConstraints(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.ConstraintExpr("linux darwin")
+	ctx.ConstraintExpr("amd64 arm64 mips64x ppc64x")
+
+	expect := []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+	}
+	if buildtags.GoBuildSyntaxSupported() {
+		expect = append(expect,
+			"//go:build (linux || darwin) && (amd64 || arm64 || mips64x || ppc64x)",
+		)
+	}
+	if buildtags.PlusBuildSyntaxSupported() {
+		expect = append(expect,
+			"// +build linux darwin",
+			"// +build amd64 arm64 mips64x ppc64x",
+		)
+	}
+	expect = append(expect,
+		"",
+		"package printer",
+		"",
+	)
+
+	AssertPrintsLines(t, ctx, printer.NewStubs, expect)
+}