bind: discover pkgconfig package name

This CL enhances gengo with the ability to discover the latest python.pc
package name and adds it to the #cgo pkgconfig pragma.

Fixes #51.

Change-Id: If4d46d6fe90731df6b2cb4f9c39fb3ec967e7330

bind/bind.go

@@ -54,12 +54,13 @@ func GenCPython(w io.Writer, fset *token.FileSet, pkg *Package, lang int) error
 }
 
 // GenGo generates a cgo package from a Go package
-func GenGo(w io.Writer, fset *token.FileSet, pkg *Package) error {
+func GenGo(w io.Writer, fset *token.FileSet, pkg *Package, lang int) error {
 	buf := new(bytes.Buffer)
 	gen := &goGen{
 		printer: &printer{buf: buf, indentEach: []byte("\t")},
 		fset:    fset,
 		pkg:     pkg,
+		lang:    lang,
 	}
 	err := gen.gen()
 	if err != nil {

bind/gengo.go

@@ -7,7 +7,6 @@ package bind
 import (
 	"fmt"
 	"go/token"
-	"path/filepath"
 	"strings"
 
 	"golang.org/x/tools/go/types"
@@ -20,7 +19,7 @@ const (
 // File is generated by gopy gen. Do not edit.
 package main
 
-//#cgo pkg-config: python2 --cflags --libs
+//#cgo pkg-config: %[3]s --cflags --libs
 //#include <stdlib.h>
 //#include <string.h>
 //#include <complex.h>
@@ -134,6 +133,7 @@ type goGen struct {
 
 	fset *token.FileSet
 	pkg  *Package
+	lang int // python's version API (2 or 3)
 	err  ErrorList
 }
 
@@ -952,7 +952,12 @@ func (g *goGen) genPreamble() {
 		pkgimport = fmt.Sprintf("_ %q", g.pkg.pkg.Path())
 	}
 
-	g.Printf(goPreamble, n, pkgimport, filepath.Base(n))
+	pkgcfg, err := getPkgConfig(g.lang)
+	if err != nil {
+		panic(err)
+	}
+
+	g.Printf(goPreamble, n, pkgimport, pkgcfg)
 }
 
 func (g *goGen) tupleString(tuple []*Var) string {

bind/utils.go

@@ -5,7 +5,13 @@
 package bind
 
 import (
+	"bufio"
+	"bytes"
 	"fmt"
+	"io"
+	"os/exec"
+	"regexp"
+	"sort"
 
 	"golang.org/x/tools/go/types"
 )
@@ -79,3 +85,67 @@ func isConstructor(sig *types.Signature) bool {
 	//TODO(sbinet)
 	return false
 }
+
+// getPkgConfig returns the name of the pkg-config python's pc file
+func getPkgConfig(vers int) (string, error) {
+	bin, err := exec.LookPath("pkg-config")
+	if err != nil {
+		return "", fmt.Errorf(
+			"gopy: could not locate 'pkg-config' executable (err: %v)",
+			err,
+		)
+	}
+
+	out, err := exec.Command(bin, "--list-all").Output()
+	if err != nil {
+		return "", fmt.Errorf(
+			"gopy: error retrieving the list of packages known to pkg-config (err: %v)",
+			err,
+		)
+	}
+
+	pkgs := []string{}
+	re := regexp.MustCompile(fmt.Sprintf(`^python(\s|-|\.|)%d.*?`, vers))
+	s := bufio.NewScanner(bytes.NewReader(out))
+	for s.Scan() {
+		err = s.Err()
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			break
+		}
+
+		line := s.Bytes()
+		if !bytes.HasPrefix(line, []byte("python")) {
+			continue
+		}
+
+		if !re.Match(line) {
+			continue
+		}
+
+		pkg := bytes.Split(line, []byte(" "))
+		pkgs = append(pkgs, string(pkg[0]))
+	}
+
+	if err != nil {
+		return "", fmt.Errorf(
+			"gopy: error scanning pkg-config output (err: %v)",
+			err,
+		)
+	}
+
+	if len(pkgs) <= 0 {
+		return "", fmt.Errorf(
+			"gopy: could not find pkg-config file (no python.pc installed?)",
+		)
+	}
+
+	sort.Strings(pkgs)
+
+	// FIXME(sbinet): make sure we take the latest version?
+	pkgcfg := pkgs[0]
+
+	return pkgcfg, nil
+}

gen.go

@@ -40,6 +40,18 @@ func genPkg(odir string, p *bind.Package, lang string) error {
 		// no-op
 	}
 
+	pyvers := 2
+	switch lang {
+	case "python2", "py2":
+		pyvers = 2
+	case "python3", "py3":
+		pyvers = 3
+	}
+
+	if err != nil {
+		return err
+	}
+
 	switch lang {
 	case "python2", "py2":
 		o, err = os.Create(filepath.Join(odir, p.Name()+".c"))
@@ -62,7 +74,7 @@ func genPkg(odir string, p *bind.Package, lang string) error {
 		}
 		defer o.Close()
 
-		err = bind.GenGo(o, fset, p)
+		err = bind.GenGo(o, fset, p, pyvers)
 		if err != nil {
 			return err
 		}