Use builtin go buildinfo for git information

This makes things more workable with offbeat build procedures
eg package managers that might not fetch the repo from git,
golang autoembeds this info when available & fails gracefully when not,
or when manually requested with `-buildinfo=false` or `-buildvcs=false`
(this is what gentoo does)

Makefile

@@ -1,11 +1,4 @@
 NOW_RFC3339 = $(shell date -u +"%Y-%m-%dT%H:%M:%SZ")
-GIT_SHA = $(shell git rev-parse HEAD 2>/dev/null || no_git)
-GIT_BRANCH = $(shell git symbolic-ref --short HEAD 2>/dev/null ||:)
-ifneq ($(GIT_BRANCH),)
-GIT_COMMIT = $(GIT_SHA) ($(GIT_BRANCH))
-else
-GIT_COMMIT = $(GIT_SHA)
-endif
 
 all: build cmddocs
 
@@ -15,7 +8,7 @@ generate:
 
 build: generate
 	@echo Running Build
-	go build -o bin/flyctl -ldflags="-X 'github.com/superfly/flyctl/internal/buildinfo.buildDate=$(NOW_RFC3339)' -X 'github.com/superfly/flyctl/internal/buildinfo.commit=$(GIT_COMMIT)'" .
+	go build -o bin/flyctl -ldflags="-X 'github.com/superfly/flyctl/internal/buildinfo.buildDate=$(NOW_RFC3339)'" .
 
 test: FORCE
 	go test ./... -ldflags="-X 'github.com/superfly/flyctl/internal/buildinfo.buildDate=$(NOW_RFC3339)'" --run=$(T)

internal/buildinfo/version.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"strconv"
 	"time"
+	"runtime/debug"
 
 	"github.com/blang/semver"
 	"github.com/superfly/flyctl/terminal"
@@ -13,7 +14,6 @@ import (
 var (
 	buildDate = "<date>"
 	version   = "<version>"
-	commit    = "<commit>"
 )
 
 var (
@@ -66,7 +66,22 @@ func loadMeta() {
 }
 
 func Commit() string {
-	return commit
+	info, _ := debug.ReadBuildInfo();
+	var rev string = "<none>";
+	var dirty string = "";
+	for _, v := range info.Settings {
+		if v.Key == "vcs.revision" {
+			rev = v.Value;
+		}
+		if v.Key == "vcs.modified" {
+			if v.Value == "true" {
+				dirty = "-dirty"
+			} else {
+				dirty = "";
+			}
+		}
+	}
+	return rev + dirty;
 }
 
 func Version() semver.Version {

internal/buildinfo/version_test.go

@@ -12,22 +12,18 @@ func TestProdMeta(t *testing.T) {
 	environment = "production"
 	version = "1.2.3"
 	buildDate = "2020-06-05T13:32:23Z"
-	commit = "c8f7b8f"
 
 	loadMeta()
 
 	assert.Equal(t, "1.2.3", Version().String())
 	assert.Equal(t, "2020-06-05T13:32:23Z", BuildDate().Format(time.RFC3339))
-	assert.Equal(t, "c8f7b8f", Commit())
 }
 
 func TestDevMeta(t *testing.T) {
 	environment = "development"
 	version = "<version>"
-	commit = "<commit>"
 
 	loadMeta()
 
 	assert.Equal(t, fmt.Sprintf("0.0.0-%d+dev", BuildDate().Unix()), Version().String())
-	assert.Equal(t, "<commit>", Commit())
 }