utils: Add a git-r utility for mapping svn revisions to git revisions in the monorepo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305598 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/utils/git-svn/git-r/git-r.go b/utils/git-svn/git-r/git-r.go
new file mode 100644 (file)
index 0000000..fb641c9
--- /dev/null
+++ b/utils/git-svn/git-r/git-r.go
@@ -0,0 +1,169 @@
+//===- git-r.go - svn revisions to git revisions --------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is a small program for mapping svn revisions to git revisions in the
+// monorepo.
+//
+// To set up:
+// 1) http://llvm.org/docs/GettingStarted.html#for-developers-to-work-with-a-git-monorepo
+//    and make sure to follow the instructions for fetching commit notes.
+// 2) go build
+// 3) cp git-r ~/bin
+//
+// To use:
+// $ git r 1
+// 09c4b68e68c4fcff64b00e1ac077c4f4a524cbcc
+//
+//===----------------------------------------------------------------------===//
+
+package main
+
+import (
+       "bufio"
+       "bytes"
+       "encoding/gob"
+       "fmt"
+       "log"
+       "os"
+       "os/exec"
+       "strconv"
+       "strings"
+)
+
+func git(args ...string) (*bytes.Buffer, error) {
+       cmd := exec.Command("git", args...)
+
+       var b bytes.Buffer
+       cmd.Stdout = &b
+       err := cmd.Run()
+
+       return &b, err
+}
+
+func mkrevmap() []string {
+       revs, err := git("grep", "git-svn-rev", "refs/notes/commits")
+       if err != nil {
+               panic(err)
+       }
+
+       var revmap []string
+
+       scanner := bufio.NewScanner(revs)
+       for scanner.Scan() {
+               // refs/notes/commits:00/0b/d4acb454290301c140a1d9c4f7a45aa2fa9c:git-svn-rev: 37235
+
+               bits := strings.Split(scanner.Text(), ":")
+               gitrev := strings.Replace(bits[1], "/", "", -1)
+               svnrev := bits[3][1:]
+
+               svnrevn, err := strconv.Atoi(svnrev)
+               if err != nil {
+                       panic(err)
+               }
+
+               if svnrevn >= len(revmap) {
+                       newrevmap := make([]string, svnrevn+1)
+                       copy(newrevmap, revmap)
+                       revmap = newrevmap
+               }
+               revmap[svnrevn] = gitrev
+       }
+
+       return revmap
+}
+
+type revmap struct {
+       Noterev string
+       Revs    []string
+}
+
+func writerevmap(path string, rmap *revmap, svnrev int) {
+       noterevbuf, err := git("rev-parse", "refs/notes/commits")
+       if err != nil {
+               fmt.Fprintf(os.Stderr, "%s: could not find refs/notes/commits, see instructions:\n", os.Args[0])
+               fmt.Fprintln(os.Stderr, "http://llvm.org/docs/GettingStarted.html#for-developers-to-work-with-a-git-monorepo")
+               os.Exit(1)
+       }
+       noterev := noterevbuf.String()
+       noterev = noterev[:len(noterev)-1]
+
+       if rmap == nil || rmap.Noterev != noterev {
+               var newrmap revmap
+               newrmap.Revs = mkrevmap()
+               newrmap.Noterev = noterev
+
+               f, err := os.Create(path)
+               if err != nil {
+                       panic(err)
+               }
+
+               enc := gob.NewEncoder(f)
+               err = enc.Encode(newrmap)
+               if err != nil {
+                       os.Remove(path)
+                       panic(err)
+               }
+
+               rmap = &newrmap
+       }
+
+       if svnrev >= len(rmap.Revs) || rmap.Revs[svnrev] == "" {
+               fmt.Fprintf(os.Stderr, "%s: %d: unknown revision\n", os.Args[0], svnrev)
+               os.Exit(1)
+       }
+
+       fmt.Println(rmap.Revs[svnrev])
+}
+
+func main() {
+       if len(os.Args) != 2 {
+               fmt.Fprintf(os.Stderr, "%s: expected a single argument\n", os.Args[0])
+               os.Exit(1)
+       }
+       svnrev, err := strconv.Atoi(os.Args[1])
+       if err != nil {
+               fmt.Fprintf(os.Stderr, "%s: %s: expected an integer argument\n", os.Args[0], os.Args[1])
+               os.Exit(1)
+       }
+
+       gitdirbuf, err := git("rev-parse", "--git-common-dir")
+       if err != nil {
+               fmt.Fprintf(os.Stderr, "%s: not in a git repository\n", os.Args[0])
+               os.Exit(1)
+       }
+
+       gitdir := gitdirbuf.String()
+       gitdir = gitdir[:len(gitdir)-1]
+       err = os.Chdir(gitdir)
+       if err != nil {
+               panic(err)
+       }
+
+       mappath := "git-svn-revmap-cache"
+       f, err := os.Open(mappath)
+       if err != nil {
+               writerevmap(mappath, nil, svnrev)
+               return
+       }
+
+       dec := gob.NewDecoder(f)
+       var rmap revmap
+       err = dec.Decode(&rmap)
+       if err != nil {
+               writerevmap(mappath, nil, svnrev)
+               return
+       }
+
+       if svnrev < len(rmap.Revs) && rmap.Revs[svnrev] != "" {
+               fmt.Println(rmap.Revs[svnrev])
+               return
+       }
+
+       writerevmap(mappath, &rmap, svnrev)
+}