ast,build: add build constraints to File

Updates #3

ast.go

@@ -3,6 +3,7 @@ package avo
 import (
 	"errors"
 
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/gotypes"
 	"github.com/mmcloughlin/avo/operand"
 	"github.com/mmcloughlin/avo/reg"
@@ -94,8 +95,9 @@ type Section interface {
 
 // File represents an assembly file.
 type File struct {
-	Includes []string
+	Constraints buildtags.Constraints
-	Sections []Section
+	Includes    []string
+	Sections    []Section
 }
 
 func NewFile() *File {

build/context.go

@@ -5,6 +5,7 @@ import (
 	"go/types"
 
 	"github.com/mmcloughlin/avo"
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/gotypes"
 	"github.com/mmcloughlin/avo/operand"
 	"github.com/mmcloughlin/avo/reg"
@@ -46,6 +47,28 @@ func (c *Context) Package(path string) {
 	c.pkg = pkg
 }
 
+func (c *Context) BuildConstraints(t buildtags.ConstraintsConvertable) {
+	cs := t.ToConstraints()
+	if err := cs.Validate(); err != nil {
+		c.AddError(err)
+		return
+	}
+	c.file.Constraints = cs
+}
+
+func (c *Context) BuildConstraint(t buildtags.ConstraintConvertable) {
+	c.BuildConstraints(append(c.file.Constraints, t.ToConstraint()))
+}
+
+func (c *Context) BuildConstraintExpr(expr string) {
+	constraint, err := buildtags.ParseConstraint(expr)
+	if err != nil {
+		c.AddError(err)
+		return
+	}
+	c.BuildConstraint(constraint)
+}
+
 func (c *Context) Function(name string) {
 	c.function = avo.NewFunction(name)
 	c.file.AddSection(c.function)

build/global.go

@@ -4,6 +4,7 @@ import (
 	"flag"
 	"os"
 
+	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/gotypes"
 	"github.com/mmcloughlin/avo/operand"
 
@@ -52,6 +53,10 @@ func Generate() {
 	}
 }
 
+func BuildConstraints(t buildtags.ConstraintsConvertable) { ctx.BuildConstraints(t) }
+func BuildConstraint(t buildtags.ConstraintConvertable)   { ctx.BuildConstraint(t) }
+func BuildConstraintExpr(expr string)                     { ctx.BuildConstraintExpr(expr) }
+
 func GP8v() reg.GPVirtual  { return ctx.GP8v() }
 func GP16v() reg.GPVirtual { return ctx.GP16v() }
 func GP32v() reg.GPVirtual { return ctx.GP32v() }

printer/goasm.go

@@ -22,8 +22,7 @@ func NewGoAsm(cfg Config) Printer {
 }
 
 func (p *goasm) Print(f *avo.File) ([]byte, error) {
-	p.header()
+	p.header(f)
-	p.includes(f.Includes)
 	for _, s := range f.Sections {
 		switch s := s.(type) {
 		case *avo.Function:
@@ -37,15 +36,21 @@ func (p *goasm) Print(f *avo.File) ([]byte, error) {
 	return p.Result()
 }
 
-func (p *goasm) header() {
+func (p *goasm) header(f *avo.File) {
 	p.Comment(p.cfg.GeneratedWarning())
+
+	if len(f.Constraints) > 0 {
+		p.NL()
+		p.Printf(f.Constraints.GoString())
+	}
+
+	if len(f.Includes) > 0 {
+		p.NL()
+		p.includes(f.Includes)
+	}
 }
 
 func (p *goasm) includes(paths []string) {
-	if len(paths) == 0 {
-		return
-	}
-	p.NL()
 	for _, path := range paths {
 		p.Printf("#include \"%s\"\n", path)
 	}

printer/goasm_test.go

@@ -67,3 +67,17 @@ func TestTextDecl(t *testing.T) {
 		"",
 	})
 }
+
+func TestConstraints(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.BuildConstraintExpr("linux,386 darwin,!cgo")
+	ctx.BuildConstraintExpr("!noasm")
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"// +build linux,386 darwin,!cgo",
+		"// +build !noasm",
+		"",
+	})
+}