Some basic git objects.

Author: apenwarr

go.mod

@@ -0,0 +1,9 @@
+module github.com/apenwarr/git_subtrac
+
+go 1.12
+
+require (
+	github.com/src-d/go-git v4.7.0+incompatible
+	golang.org/x/crypto v0.0.0-20191108234033-bd318be0434a // indirect
+	gopkg.in/src-d/go-git.v4 v4.13.1
+)

go.sum

@@ -0,0 +1,63 @@
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subtrac.go

@@ -0,0 +1,99 @@
+package main
+
+import (
+	"fmt"
+	//	"github.com/pborman/getopt/v2"
+	"gopkg.in/src-d/go-git.v4"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"log"
+	"strings"
+)
+
+func debugf(fmt string, args ...interface{}) {
+	log.Printf(fmt, args...)
+}
+
+func fatalf(fmt string, args ...interface{}) {
+	log.Fatalf("git-subtrac: "+fmt, args...)
+}
+
+type Trac struct {
+	commit     object.Commit
+	subHeads   []Trac
+	tracCommit *object.Commit
+}
+
+func (t Trac) String() string {
+	var heads []string
+	for _, v := range t.subHeads {
+		heads = append(heads, fmt.Sprintf("%.10v", v.commit.Hash))
+	}
+	headstr := strings.Join(heads, ",")
+
+	if t.tracCommit != nil {
+		return fmt.Sprintf("%.10v[%v]<%.10v>",
+			t.commit.Hash, headstr, t.tracCommit.Hash)
+	} else {
+		return fmt.Sprintf("%.10v[%v]<>", t.commit.Hash, headstr)
+	}
+}
+
+type Cache struct {
+	repo  *git.Repository
+	tracs map[plumbing.Hash]Trac
+}
+
+func NewCache(r *git.Repository) *Cache {
+	c := Cache{
+		repo:  r,
+		tracs: make(map[plumbing.Hash]Trac),
+	}
+	return &c
+}
+
+func (c *Cache) String() string {
+	var out []string
+	for _, v := range c.tracs {
+		out = append(out, v.String())
+	}
+	return strings.Join(out, "\n")
+}
+
+// Mercifully, git's content-addressable storage means there are never
+// any cycles when traversing the commit+submodule hierarchy, although the
+// same sub-objects may occur many times at different points in the tree.
+func (c *Cache) Add(commit *object.Commit) error {
+	c.tracs[commit.Hash] = Trac{
+		commit: *commit,
+	}
+	return nil
+}
+
+func (c *Cache) AddByRef(refname string) error {
+	rn := plumbing.NewBranchReferenceName(refname)
+	ref, err := c.repo.Reference(rn, true)
+	if err != nil {
+		return err
+	}
+	commit, err := c.repo.CommitObject(ref.Hash())
+	if err != nil {
+		return err
+	}
+	return c.Add(commit)
+}
+
+func main() {
+	log.SetFlags(0)
+	r, err := git.PlainOpen(".")
+	if err != nil {
+		fatalf("git.PlainOpen: %v\n", err)
+	}
+	c := NewCache(r)
+	refname := "junk"
+	err = c.AddByRef(refname)
+	if err != nil {
+		fatalf("AddByRef: %v: %v\n", refname, err)
+	}
+	debugf("cache:\n%v\n", c)
+}