Fix revision solver for branch and tag (#660)

fix Repository.ResolveRevision for branch and tag

7 files changed, 82 insertions, 54 deletions

diff --git a/_examples/README.md b/_examples/README.md
index 10594ab..271379b 100644
--- a/_examples/README.md
+++ b/_examples/README.md
@@ -11,9 +11,10 @@ Here you can find a list of annotated _go-git_ examples:
 - [remotes](remotes/main.go) - Working with remotes: adding, removing, etc
 - [progress](progress/main.go) - Printing the progress information from the sideband
 - [push](push/main.go) - Push repository to default remote (origin)
-- [checkout](checkout/main.go) - check out a specific commit from a repository
-- [tag](tag/main.go) - list/print repository tags
-- [pull](pull/main.go) - pull changes from a remote repository
+- [checkout](checkout/main.go) - Check out a specific commit from a repository
+- [tag](tag/main.go) - List/print repository tags
+- [pull](pull/main.go) - Pull changes from a remote repository
+- [revision](revision/main.go) - Solve a revision into a commit
 ### Advanced
 - [custom_http](custom_http/main.go) - Replacing the HTTP client using a custom one
 - [storage](storage/README.md) - Implementing a custom storage system
diff --git a/_examples/common.go b/_examples/common.go
index 2719c0e..81ed647 100644
--- a/_examples/common.go
+++ b/_examples/common.go
@@ -6,7 +6,7 @@ import (
 	"strings"
 )
 
-// CheckArgs should be used to esnure the right command line arguments are
+// CheckArgs should be used to ensure the right command line arguments are
 // passed before executing an example.
 func CheckArgs(arg ...string) {
 	if len(os.Args) < len(arg)+1 {
diff --git a/_examples/common_test.go b/_examples/common_test.go
index d164297..6f8df45 100644
--- a/_examples/common_test.go
+++ b/_examples/common_test.go
@@ -23,6 +23,7 @@ var args = map[string][]string{
 	"open":        {cloneRepository(defaultURL, tempFolder())},
 	"progress":    {defaultURL, tempFolder()},
 	"push":        {setEmptyRemote(cloneRepository(defaultURL, tempFolder()))},
+	"revision":    {cloneRepository(defaultURL, tempFolder()), "master~2^"},
 	"showcase":    {defaultURL, tempFolder()},
 	"tag":         {cloneRepository(defaultURL, tempFolder())},
 	"pull":        {createRepositoryWithRemote(tempFolder(), defaultURL)},
diff --git a/_examples/revision/main.go b/_examples/revision/main.go
new file mode 100644
index 0000000..a2389bd
--- /dev/null
+++ b/_examples/revision/main.go
@@ -0,0 +1,32 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"gopkg.in/src-d/go-git.v4"
+	. "gopkg.in/src-d/go-git.v4/_examples"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+// Example how to resolve a revision into its commit counterpart
+func main() {
+	CheckArgs("<path>", "<revision>")
+
+	path := os.Args[1]
+	revision := os.Args[2]
+
+	// We instantiate a new repository targeting the given path (the .git folder)
+	r, err := git.PlainOpen(path)
+	CheckIfError(err)
+
+	// Resolve revision into a sha1 commit, only some revisions are resolved
+	// look at the doc to get more details
+	Info("git rev-parse %s", revision)
+
+	h, err := r.ResolveRevision(plumbing.Revision(revision))
+
+	CheckIfError(err)
+
+	fmt.Println(h.String())
+}
diff --git a/plumbing/reference.go b/plumbing/reference.go
index 2c30fe0..2f53d4e 100644
--- a/plumbing/reference.go
+++ b/plumbing/reference.go
@@ -15,10 +15,10 @@ const (
 	symrefPrefix    = "ref: "
 )
 
-// refRevParseRules are a set of rules to parse references into short names.
+// RefRevParseRules are a set of rules to parse references into short names.
 // These are the same rules as used by git in shorten_unambiguous_ref.
 // See: https://github.com/git/git/blob/e0aaa1b6532cfce93d87af9bc813fb2e7a7ce9d7/refs.c#L417
-var refRevParseRules = []string{
+var RefRevParseRules = []string{
 	"refs/%s",
 	"refs/tags/%s",
 	"refs/heads/%s",
@@ -83,7 +83,7 @@ func (r ReferenceName) String() string {
 func (r ReferenceName) Short() string {
 	s := string(r)
 	res := s
-	for _, format := range refRevParseRules {
+	for _, format := range RefRevParseRules {
 		_, err := fmt.Sscanf(s, format, &res)
 		if err == nil {
 			continue
diff --git a/repository.go b/repository.go
index 7cdc0d5..8a966c6 100644
--- a/repository.go
+++ b/repository.go
@@ -891,6 +891,9 @@ func (r *Repository) Worktree() (*Worktree, error) {
 }
 
 // ResolveRevision resolves revision to corresponding hash.
+//
+// Implemented resolvers : HEAD, branch, tag, heads/branch, refs/heads/branch,
+// refs/tags/tag, refs/remotes/origin/branch, refs/remotes/origin/HEAD, tilde and caret (HEAD~1, master~^, tag~2, ref/heads/master~1, ...), selection by text (HEAD^{/fix nasty bug})
 func (r *Repository) ResolveRevision(rev plumbing.Revision) (*plumbing.Hash, error) {
 	p := revision.NewParserFromString(string(rev))
 
@@ -905,15 +908,22 @@ func (r *Repository) ResolveRevision(rev plumbing.Revision) (*plumbing.Hash, err
 	for _, item := range items {
 		switch item.(type) {
 		case revision.Ref:
-			ref, err := storer.ResolveReference(r.Storer, plumbing.ReferenceName(item.(revision.Ref)))
+			revisionRef := item.(revision.Ref)
+			var ref *plumbing.Reference
 
-			if err != nil {
-				return &plumbing.ZeroHash, err
+			for _, rule := range append([]string{"%s"}, plumbing.RefRevParseRules...) {
+				ref, err = storer.ResolveReference(r.Storer, plumbing.ReferenceName(fmt.Sprintf(rule, revisionRef)))
+
+				if err == nil {
+					break
+				}
 			}
 
-			h := ref.Hash()
+			if ref == nil {
+				return &plumbing.ZeroHash, plumbing.ErrReferenceNotFound
+			}
 
-			commit, err = r.CommitObject(h)
+			commit, err = r.CommitObject(ref.Hash())
 
 			if err != nil {
 				return &plumbing.ZeroHash, err
@@ -986,29 +996,6 @@ func (r *Repository) ResolveRevision(rev plumbing.Revision) (*plumbing.Hash, err
 			}
 
 			commit = c
-		case revision.AtDate:
-			history := object.NewCommitPreorderIter(commit, nil, nil)
-
-			date := item.(revision.AtDate).Date
-
-			var c *object.Commit
-			err := history.ForEach(func(hc *object.Commit) error {
-				if date.Equal(hc.Committer.When.UTC()) || hc.Committer.When.UTC().Before(date) {
-					c = hc
-					return storer.ErrStop
-				}
-
-				return nil
-			})
-			if err != nil {
-				return &plumbing.ZeroHash, err
-			}
-
-			if c == nil {
-				return &plumbing.ZeroHash, fmt.Errorf(`No commit exists prior to date "%s"`, date.String())
-			}
-
-			commit = c
 		}
 	}
 
diff --git a/repository_test.go b/repository_test.go
index 2ebc597..cf0805a 100644
--- a/repository_test.go
+++ b/repository_test.go
@@ -1265,24 +1265,32 @@ func (s *RepositorySuite) TestWorktreeBare(c *C) {
 }
 
 func (s *RepositorySuite) TestResolveRevision(c *C) {
-	url := s.GetLocalRepositoryURL(
-		fixtures.ByURL("https://github.com/git-fixtures/basic.git").One(),
-	)
-
-	r, _ := Init(memory.NewStorage(), nil)
-	err := r.clone(context.Background(), &CloneOptions{URL: url})
+	f := fixtures.ByURL("https://github.com/git-fixtures/basic.git").One()
+	sto, err := filesystem.NewStorage(f.DotGit())
+	c.Assert(err, IsNil)
+	r, err := Open(sto, f.DotGit())
 	c.Assert(err, IsNil)
 
 	datas := map[string]string{
-		"HEAD": "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
-		"refs/heads/master~2^^~":      "b029517f6300c2da0f4b651b8642506cd6aaf45d",
-		"HEAD~2^^~":                   "b029517f6300c2da0f4b651b8642506cd6aaf45d",
-		"HEAD~3^2":                    "a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
-		"HEAD~3^2^0":                  "a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
-		"HEAD~2^{/binary file}":       "35e85108805c84807bc66a02d91535e1e24b38b9",
-		"HEAD~^{!-some}":              "1669dce138d9b841a518c64b10914d88f5e488ea",
-		"HEAD@{2015-03-31T11:56:18Z}": "918c48b83bd081e863dbe1b80f8998f058cd8294",
-		"HEAD@{2015-03-31T11:49:00Z}": "1669dce138d9b841a518c64b10914d88f5e488ea",
+		"HEAD":                       "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"heads/master":               "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"heads/master~1":             "918c48b83bd081e863dbe1b80f8998f058cd8294",
+		"refs/heads/master":          "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"refs/heads/master~2^^~":     "b029517f6300c2da0f4b651b8642506cd6aaf45d",
+		"refs/tags/v1.0.0":           "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"refs/remotes/origin/master": "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"refs/remotes/origin/HEAD":   "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"HEAD~2^^~":                  "b029517f6300c2da0f4b651b8642506cd6aaf45d",
+		"HEAD~3^2":                   "a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
+		"HEAD~3^2^0":                 "a5b8b09e2f8fcb0bb99d3ccb0958157b40890d69",
+		"HEAD~2^{/binary file}":      "35e85108805c84807bc66a02d91535e1e24b38b9",
+		"HEAD~^{/!-some}":            "1669dce138d9b841a518c64b10914d88f5e488ea",
+		"master":                     "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"branch":                     "e8d3ffab552895c19b9fcf7aa264d277cde33881",
+		"v1.0.0":                     "6ecf0ef2c2dffb796033e5a02219af86ec6584e5",
+		"branch~1":                   "918c48b83bd081e863dbe1b80f8998f058cd8294",
+		"v1.0.0~1":                   "918c48b83bd081e863dbe1b80f8998f058cd8294",
+		"master~1":                   "918c48b83bd081e863dbe1b80f8998f058cd8294",
 	}
 
 	for rev, hash := range datas {
@@ -1303,10 +1311,9 @@ func (s *RepositorySuite) TestResolveRevisionWithErrors(c *C) {
 	c.Assert(err, IsNil)
 
 	datas := map[string]string{
-		"efs/heads/master~":           "reference not found",
-		"HEAD^3":                      `Revision invalid : "3" found must be 0, 1 or 2 after "^"`,
-		"HEAD^{/whatever}":            `No commit message match regexp : "whatever"`,
-		"HEAD@{2015-03-31T09:49:00Z}": `No commit exists prior to date "2015-03-31 09:49:00 +0000 UTC"`,
+		"efs/heads/master~": "reference not found",
+		"HEAD^3":            `Revision invalid : "3" found must be 0, 1 or 2 after "^"`,
+		"HEAD^{/whatever}":  `No commit message match regexp : "whatever"`,
 	}
 
 	for rev, rerr := range datas {