git tags and diff

git/log.go

@@ -0,0 +1,18 @@
+package git
+
+import "os/exec"
+
+func Log(previous, current string) (str string, err error) {
+	cmd := exec.Command(
+		"git",
+		"log",
+		"--pretty=oneline",
+		"--abbrev-commit",
+		previous+".."+current,
+	)
+	bts, err := cmd.CombinedOutput()
+	if err != nil {
+		return str, err
+	}
+	return string(bts), err
+}

git/tag.go

@@ -0,0 +1,34 @@
+package git
+
+import (
+	"os/exec"
+	"strings"
+)
+
+func CurrentTag() (tag string, err error) {
+	return getTag("master")
+}
+
+func PreviousTag() (tag string, err error) {
+	current, err := CurrentTag()
+	if err != nil {
+		return tag, err
+	}
+	return getTag(current + "^")
+}
+
+func getTag(ref string) (tag string, err error) {
+	cmd := exec.Command(
+		"git",
+		"describe",
+		"--tags",
+		"--abbrev=0",
+		"--always",
+		ref,
+	)
+	bts, err := cmd.CombinedOutput()
+	if err != nil {
+		return tag, err
+	}
+	return strings.Split(string(bts), "\n")[0], err
+}

main.go

@@ -2,9 +2,11 @@ package main
 
 import (
 	"fmt"
+	"log"
 
 	"github.com/goreleaser/releaser/build"
 	"github.com/goreleaser/releaser/config"
+	"github.com/goreleaser/releaser/git"
 )
 
 var version = "none"
@@ -14,6 +16,17 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
-	err = build.Build("master", config)
+	tag, err := git.CurrentTag()
+	if err != nil {
+		panic(err)
+	}
+	previousTag, err := git.PreviousTag()
+	diff, err := git.Log(previousTag, tag)
+	if err != nil {
+		panic(err)
+	}
+	log.Println(diff)
+	fmt.Println("Building", tag, "...")
+	err = build.Build(tag, config)
 	fmt.Println(err)
 }