cgo.go

package langd

import (
	"fmt"
	"go/build"
	"os"
	"os/exec"
	"regexp"
	"strings"

	"github.com/pkg/errors"
)

var cgoRe = regexp.MustCompile(`[/\\:]`)

// Return the flags to use when invoking the C or C++ compilers, or cgo.
func cflags(p *build.Package, def bool) (cppflags, cflags, cxxflags, ldflags []string) {
	var defaults string
	if def {
		defaults = "-g -O2"
	}

	cppflags = stringList(envList("CGO_CPPFLAGS", ""), p.CgoCPPFLAGS)
	cflags = stringList(envList("CGO_CFLAGS", defaults), p.CgoCFLAGS)
	cxxflags = stringList(envList("CGO_CXXFLAGS", defaults), p.CgoCXXFLAGS)
	ldflags = stringList(envList("CGO_LDFLAGS", defaults), p.CgoLDFLAGS)
	return
}

// envList returns the value of the given environment variable broken
// into fields, using the default value when the variable is empty.
func envList(key, def string) []string {
	v := os.Getenv(key)
	if v == "" {
		v = def
	}
	return strings.Fields(v)
}

// stringList's arguments should be a sequence of string or []string values.
// stringList flattens them into a single []string.
func stringList(args ...interface{}) []string {
	var x []string
	for _, arg := range args {
		switch arg := arg.(type) {
		case []string:
			x = append(x, arg...)
		case string:
			x = append(x, arg)
		default:
			panic("stringList: invalid argument")
		}
	}
	return x
}

// pkgConfig runs pkg-config with the specified arguments and returns the flags it prints.
func pkgConfig(mode string, pkgs []string) (flags []string, err error) {
	cmd := exec.Command("pkg-config", append([]string{mode}, pkgs...)...)
	out, err := cmd.CombinedOutput()
	if err != nil {
		s := fmt.Sprintf("%s failed: %v", strings.Join(cmd.Args, " "), err)
		if len(out) > 0 {
			s = fmt.Sprintf("%s: %s", s, out)
		}
		return nil, errors.New(s)
	}
	if len(out) > 0 {
		flags = strings.Fields(string(out))
	}
	return
}

// pkgConfigFlags calls pkg-config if needed and returns the cflags
// needed to build the package.
func pkgConfigFlags(p *build.Package) (cflags []string, err error) {
	if len(p.CgoPkgConfig) == 0 {
		return nil, nil
	}
	return pkgConfig("--cflags", p.CgoPkgConfig)
}