Support shortened commit SHAs in URLs (go-gitea#6450)

This supports using a git SHA of any length between 7 and 40
characters in URLs (e.g. /src/commit/SHA/...).  Previously
only commit SHAs of the full 40 character length were supported.

The RepoRefAny ref type is used in one place, in the
/api/v1/user/repo/raw API endpoint where it is used to guess whether
the remainder of the path is a ref name followed by a file path
or merely a file path.  There is no good way to guess whether
a shortened SHA is intended in that circumstance (e.g.,
/raw/beefcafe/README.txt could be /README.txt in the beefcafe{..32}
commit, or /beefcafe/README.txt on the master branch).  For this
case, we don't support shortened SHAs and only match on the full
one.

Signed-off-by: James E. Blair <jeblair@redhat.com>

modules/context/repo.go

@@ -475,8 +475,10 @@ const (
 	RepoRefBranch
 	// RepoRefTag tag
 	RepoRefTag
-	// RepoRefCommit commit
+	// RepoRefCommit short or long commit
 	RepoRefCommit
+	// RepoRefFullCommit long commit only
+	RepoRefFullCommit
 	// RepoRefBlob blob
 	RepoRefBlob
 )
@@ -511,7 +513,7 @@ func getRefName(ctx *Context, pathType RepoRefType) string {
 		if refName := getRefName(ctx, RepoRefTag); len(refName) > 0 {
 			return refName
 		}
-		if refName := getRefName(ctx, RepoRefCommit); len(refName) > 0 {
+		if refName := getRefName(ctx, RepoRefFullCommit); len(refName) > 0 {
 			return refName
 		}
 		if refName := getRefName(ctx, RepoRefBlob); len(refName) > 0 {
@@ -523,12 +525,18 @@ func getRefName(ctx *Context, pathType RepoRefType) string {
 		return getRefNameFromPath(ctx, path, ctx.Repo.GitRepo.IsBranchExist)
 	case RepoRefTag:
 		return getRefNameFromPath(ctx, path, ctx.Repo.GitRepo.IsTagExist)
-	case RepoRefCommit:
+	case RepoRefFullCommit:
 		parts := strings.Split(path, "/")
 		if len(parts) > 0 && len(parts[0]) == 40 {
 			ctx.Repo.TreePath = strings.Join(parts[1:], "/")
 			return parts[0]
 		}
+	case RepoRefCommit:
+		parts := strings.Split(path, "/")
+		if len(parts) > 0 && len(parts[0]) >= 7 && len(parts[0]) <= 40 {
+			ctx.Repo.TreePath = strings.Join(parts[1:], "/")
+			return parts[0]
+		}
 	case RepoRefBlob:
 		_, err := ctx.Repo.GitRepo.GetBlob(path)
 		if err != nil {
@@ -611,7 +619,7 @@ func RepoRefByType(refType RepoRefType) macaron.Handler {
 					return
 				}
 				ctx.Repo.CommitID = ctx.Repo.Commit.ID.String()
-			} else if len(refName) == 40 {
+			} else if len(refName) >= 7 && len(refName) <= 40 {
 				ctx.Repo.IsViewCommit = true
 				ctx.Repo.CommitID = refName