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

llvm-svn: 305598

llvm/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)
+}