Rebase — history নতুন করে সাজানো, interactive rebase আর merge বনাম rebase

// Rebase = replay commits on a new base, in a tiny commit DAG. fnv1a stands in for
// Git's SHA-1, which hashes the whole commit object; here only parent + change.
function fnv1a(s) {
  let h = 0x811c9dc5;
  for (const ch of s) { h ^= ch.charCodeAt(0); h = Math.imul(h, 0x01000193) >>> 0; }
  return h.toString(16).padStart(8, "0").slice(0, 7);
}
const commits = {}, refs = {};                 // id -> {parent, change}
function commit(parent, change) {
  const id = fnv1a((parent || "root") + "|" + change);
  commits[id] = { parent, change };
  return id;
}
function history(id) { const h = []; for (; id; id = commits[id].parent) h.push(id); return h; }
const A = commit(null, "add portal.conf"), B = commit(A, "add README");
refs.main = commit(B, "README: add contact");           // E on main
refs.feature = commit(commit(B, "add gpa.txt"), "show GPA"); // C, D on feature
console.log("before: feature =", history(refs.feature).join(" <- "));
function rebase(branch, onto) {
  if (history(refs[branch]).includes(refs[onto])) return console.log("  " + branch + " is up to date");
  const onBase = new Set(history(refs[onto])), todo = [];
  for (let id = refs[branch]; !onBase.has(id); id = commits[id].parent) todo.unshift(id);
  let tip = refs[onto];
  for (const old of todo) {
    tip = commit(tip, commits[old].change);            // same change, new parent
    console.log("  replay " + old + " -> " + tip + "  (" + commits[old].change + ")");
  }
  refs.ORIG_HEAD = refs[branch]; refs[branch] = tip;
}
rebase("feature", "main");
console.log("after:  feature =", history(refs.feature).join(" <- "));
const reach = new Set([...history(refs.main), ...history(refs.feature)]);
const ghosts = Object.keys(commits).filter(id => !reach.has(id));
console.log("unreachable but still stored:", ghosts.join(", "), "| ORIG_HEAD =", refs.ORIG_HEAD);
rebase("feature", "main");                              // main is already an ancestor

$ git switch -c feature/gpa
Switched to a new branch 'feature/gpa'
# (create gpa.txt; git add gpa.txt)
$ git commit -m "Add GPA calculator"
[feature/gpa 2e9e344] Add GPA calculator
 1 file changed, 1 insertion(+)
 create mode 100644 gpa.txt
# (append a line to gpa.txt; git add gpa.txt)
$ git commit -m "Show GPA on result page"
[feature/gpa 3af94ac] Show GPA on result page
 1 file changed, 1 insertion(+)
$ git switch main
Switched to branch 'main'
# (append the contact line to README.md; git add README.md)
$ git commit -m "Add contact to README"
[main 2313ddc] Add contact to README
 1 file changed, 1 insertion(+)
$ git log --oneline --graph --all
* 2313ddc (HEAD -> main) Add contact to README
| * 3af94ac (feature/gpa) Show GPA on result page
| * 2e9e344 Add GPA calculator
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config
$ git switch feature/gpa
Switched to branch 'feature/gpa'
$ git merge-base main feature/gpa
8e9e4e7f6bce7ab2bb6af6e0b877c8d38156ad2d
$ git rebase main
Successfully rebased and updated refs/heads/feature/gpa.
$ git log --oneline --graph --all
* 2d52732 (HEAD -> feature/gpa) Show GPA on result page
* 0324b2d Add GPA calculator
* 2313ddc (main) Add contact to README
* 8e9e4e7 Add README
* 9316721 Add portal config

$ git log --oneline --graph main feature/gpa ORIG_HEAD
* 2d52732 (HEAD -> feature/gpa) Show GPA on result page
* 0324b2d Add GPA calculator
* 2313ddc (main) Add contact to README
| * 3af94ac Show GPA on result page
| * 2e9e344 Add GPA calculator
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config
$ git cat-file -t 3af94ac
commit
$ git reflog -6
2d52732 (HEAD -> feature/gpa) HEAD@{0}: rebase (finish): returning to refs/heads/feature/gpa
2d52732 (HEAD -> feature/gpa) HEAD@{1}: rebase (pick): Show GPA on result page
0324b2d HEAD@{2}: rebase (pick): Add GPA calculator
2313ddc (main) HEAD@{3}: rebase (start): checkout main
3af94ac HEAD@{4}: checkout: moving from main to feature/gpa
2313ddc (main) HEAD@{5}: commit: Add contact to README
$ git range-diff 8e9e4e7..3af94ac main..feature/gpa
1:  2e9e344 = 1:  0324b2d Add GPA calculator
2:  3af94ac = 2:  2d52732 Show GPA on result page
$ git log --format="%h %an %ad | %cd %s" --date=format:%H:%M -3
2d52732 Rahim 10:04 | 10:06 Show GPA on result page
0324b2d Rahim 10:03 | 10:06 Add GPA calculator
2313ddc Rahim 10:05 | 10:05 Add contact to README

$ git log --oneline --graph --all
* 92a039f (main) Mark pass mark as board rule
| * df28b53 (HEAD -> feature/pass-mark) Set pass mark to 50
| * 9c0a8f6 Add grace marks option
| * d080157 Set pass mark to 45
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config
$ git rebase main
Auto-merging portal.conf
CONFLICT (content): Merge conflict in portal.conf
error: could not apply d080157... Set pass mark to 45
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Could not apply d080157... # Set pass mark to 45
$ git status
interactive rebase in progress; onto 92a039f
Last command done (1 command done):
   pick d080157 # Set pass mark to 45
Next commands to do (2 remaining commands):
   pick 9c0a8f6 # Add grace marks option
   pick df28b53 # Set pass mark to 50
  (use "git rebase --edit-todo" to view and edit)
You are currently rebasing branch 'feature/pass-mark' on '92a039f'.
  (fix conflicts and then run "git rebase --continue")
  (use "git rebase --skip" to skip this patch)
  (use "git rebase --abort" to check out the original branch)

Unmerged paths:
  (use "git restore --staged <file>..." to unstage)
  (use "git add <file>..." to mark resolution)
	both modified:   portal.conf

no changes added to commit (use "git add" and/or "git commit -a")
$ cat portal.conf
title = Result Portal
<<<<<<< HEAD
pass_mark = 40  # board rule
=======
pass_mark = 45
>>>>>>> d080157 (Set pass mark to 45)
grade_scale = 5
show_rank = no

$ git rebase --abort
$ git status --short --branch
## feature/pass-mark
$ git log --oneline -1
df28b53 (HEAD -> feature/pass-mark) Set pass mark to 50

$ git rebase main
…  (the same conflict in portal.conf as above)
# (edit portal.conf: pass_mark = 45  # board rule; remove the markers)
$ git add portal.conf
# (Git opens the editor with the message "Set pass mark to 45"; save and close)
$ git rebase --continue
[detached HEAD 18cf9e6] Set pass mark to 45
 1 file changed, 1 insertion(+), 1 deletion(-)
Auto-merging portal.conf
CONFLICT (content): Merge conflict in portal.conf
error: could not apply df28b53... Set pass mark to 50
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Could not apply df28b53... # Set pass mark to 50
$ cat portal.conf
title = Result Portal
<<<<<<< HEAD
pass_mark = 45  # board rule
=======
pass_mark = 50
>>>>>>> df28b53 (Set pass mark to 50)
grade_scale = 5
show_rank = no
grace_marks = 2
# (edit again: pass_mark = 50  # board rule; remove the markers)
$ git add portal.conf
$ git rebase --continue
[detached HEAD 525683c] Set pass mark to 50
 1 file changed, 1 insertion(+), 1 deletion(-)
Successfully rebased and updated refs/heads/feature/pass-mark.
$ git log --oneline --graph --all
* 525683c (HEAD -> feature/pass-mark) Set pass mark to 50
* a100128 Add grace marks option
* 18cf9e6 Set pass mark to 45
* 92a039f (main) Mark pass mark as board rule
* 8e9e4e7 Add README
* 9316721 Add portal config
$ cat portal.conf
title = Result Portal
pass_mark = 50  # board rule
grade_scale = 5
show_rank = no
grace_marks = 2

// Rebase replays commits one by one, so one overlapping line can conflict again
// and again. A merge compares only the two final tips with their merge base.
function merge3(base, ours, theirs) {              // one-line three-way merge
  if (ours === theirs || theirs === base) return { line: ours };
  if (ours === base) return { line: theirs };
  return { conflict: true };
}
const resolve = theirs => theirs + "  # board rule"; // keep new value AND main's note
const base = "pass_mark = 40";
const mainTip = "pass_mark = 40  # board rule";
const feature = ["pass_mark = 45", "pass_mark = 50", "pass_mark = 55"]; // 3 commits

function rebaseCount(commits) {
  let tip = mainTip, parent = base, n = 0;
  for (const line of commits) {
    let r = merge3(parent, tip, line);             // base = the commit's old parent
    const hit = !!r.conflict;
    if (hit) { n++; r = { line: resolve(line) }; }
    console.log("  replay '" + line + "' ->", hit ? "resolution #" + n : "clean", "->", r.line);
    tip = r.line; parent = line;
  }
  return n;
}
console.log("rebase, 3 commits:"); const a = rebaseCount(feature);
const m = merge3(base, mainTip, feature[2]);
const b = m.conflict ? 1 : 0;
console.log("merge once: resolutions", b, "->", m.conflict ? resolve(feature[2]) : m.line);
console.log("squash first, then rebase:"); const c = rebaseCount([feature[2]]);
console.log("total resolutions -> rebase:", a, "| merge:", b, "| squash+rebase:", c);

# (meanwhile Karim pushed "Show rank on result page" to origin/main)
# (create help.txt; git add help.txt)
$ git commit -m "Add help page"
[main 5c8086f] Add help page
 1 file changed, 1 insertion(+)
 create mode 100644 help.txt
$ git push
To ../origin.git
 ! [rejected]        main -> main (fetch first)
error: failed to push some refs to '../origin.git'
hint: Updates were rejected because the remote contains work that you do not
hint: have locally. This is usually caused by another repository pushing to
hint: the same ref. If you want to integrate the remote changes, use
hint: 'git pull' before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
$ git pull --rebase
From ../origin
   8e9e4e7..8754dd6  main       -> origin/main
Successfully rebased and updated refs/heads/main.
$ git log --oneline --graph --all
* 6fb4576 (HEAD -> main) Add help page
* 8754dd6 (origin/main, origin/HEAD) Show rank on result page
* 8e9e4e7 Add README
* 9316721 Add portal config
$ git push
To ../origin.git
   8754dd6..6fb4576  main -> main

$ git log --oneline --graph --all
* d481af7 (main) Add contact to README
| * 445469e (HEAD -> feature/ui) Add print button
| * 9d34915 Add result table UI
| * aae7a7c (feature/api) Add result by roll API
| * b3e3d6b Add results API
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config
$ git rebase --onto main feature/api feature/ui
Successfully rebased and updated refs/heads/feature/ui.
$ git log --oneline --graph --all
* ba9e682 (HEAD -> feature/ui) Add print button
* 648bb82 Add result table UI
* d481af7 (main) Add contact to README
| * aae7a7c (feature/api) Add result by roll API
| * b3e3d6b Add results API
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config

# (same starting graph as above, HEAD on feature/ui)
$ git rebase --update-refs main
Successfully rebased and updated refs/heads/feature/ui.
Updated the following refs with --update-refs:
	refs/heads/feature/api
$ git log --oneline --graph --all
* 4b38fef (HEAD -> feature/ui) Add print button
* 3cabd0a Add result table UI
* 9a4854f (feature/api) Add result by roll API
* f815977 Add results API
* d481af7 (main) Add contact to README
* 8e9e4e7 Add README
* 9316721 Add portal config

$ git log --oneline
6dadb43 (HEAD -> feature/notice) Add notice categoriess
92fbb0e Debug print
8a3b36f Add date format
769758f Add notice dates
1a1ddb1 Fix typo in notice board
600a574 Add notice board
8e9e4e7 (main) Add README
9316721 Add portal config
$ git rebase -i HEAD~6
# The editor opens the todo list (comment lines trimmed):
    pick 600a574 # Add notice board
    pick 1a1ddb1 # Fix typo in notice board
    pick 769758f # Add notice dates
    pick 8a3b36f # Add date format
    pick 92fbb0e # Debug print
    pick 6dadb43 # Add notice categoriess
    
    # Rebase 8e9e4e7..6dadb43 onto 8e9e4e7 (6 commands)
    #
    # Commands:
    # p, pick <commit> = use commit
    # …
# We change it to this, save and close:
    pick 600a574 Add notice board
    fixup 1a1ddb1 Fix typo in notice board
    reword 6dadb43 Add notice categoriess
    pick 769758f Add notice dates
    squash 8a3b36f Add date format
    drop 92fbb0e Debug print
    exec ls
# reword: the editor shows "Add notice categoriess"; we fix it to "Add notice categories"
[detached HEAD a665934] Add notice categories
 Date: Thu Jan 15 10:08:00 2026 +0600
 1 file changed, 2 insertions(+)
 create mode 100644 categories.txt
# squash: the editor shows both messages; we write "Add notice dates with dd-mm-yyyy format"
[detached HEAD 78f0f9a] Add notice dates with dd-mm-yyyy format
 Date: Thu Jan 15 10:05:00 2026 +0600
 1 file changed, 2 insertions(+)
 create mode 100644 dates.txt
Executing: ls
README.md
categories.txt
dates.txt
notices.txt
portal.conf
Successfully rebased and updated refs/heads/feature/notice.

$ git log --oneline --graph --all
* 78f0f9a (HEAD -> feature/notice) Add notice dates with dd-mm-yyyy format
* a665934 Add notice categories
* 86c0eed Add notice board
* 8e9e4e7 (main) Add README
* 9316721 Add portal config
$ git log --format="%h %s" main..
78f0f9a Add notice dates with dd-mm-yyyy format
a665934 Add notice categories
86c0eed Add notice board
$ git show --stat --format="%h %s" HEAD~1
a665934 Add notice categories

 categories.txt | 2 ++
 1 file changed, 2 insertions(+)

// Interactive rebase todo interpreter: pick, reword, squash, fixup, drop.
const msg = {
  a1: "Add notice board", a2: "Fix typo in notice board", a3: "Add notice dates",
  a4: "Add date format", a5: "Debug print", a6: "Add notice categoriess"
};
function runTodo(todo) {
  const out = [];                          // new history: {from: [old ids], msg}
  for (const line of todo.trim().split("\n")) {
    const [cmd, id, ...text] = line.trim().split(/\s+/);
    const prev = out[out.length - 1];
    if (cmd === "pick") out.push({ from: [id], msg: msg[id] });
    else if (cmd === "reword") out.push({ from: [id], msg: text.join(" ") }); // Git asks in an editor
    else if (cmd === "squash" || cmd === "fixup") {
      if (!prev) throw new Error("cannot '" + cmd + "' without a previous commit");
      prev.from.push(id);
      if (cmd === "squash") prev.msg += " / " + msg[id];  // Git lets you edit both messages
    } else if (cmd !== "drop") throw new Error("unknown command " + cmd);
  }
  return out;
}
const todo = `
pick a1
fixup a2
reword a6 Add notice categories
pick a3
squash a4
drop a5`;
runTodo(todo).forEach((c, i) =>
  console.log((i + 1) + ". " + c.msg.padEnd(36) + "<- " + c.from.join("+")));
const todo2 = todo.replace("drop a5", "");            // delete the line instead
const lost = Object.keys(msg).filter(id => !todo2.includes(" " + id));
console.log("line deleted from the todo -> commit lost:", lost.join(", "));
try { runTodo("fixup a2\npick a1"); } catch (e) { console.log("error:", e.message); }

# (create login.txt; git add)
$ git commit -m "Add login page"
[feature/login 5631ab5] Add login page
 1 file changed, 1 insertion(+)
 create mode 100644 login.txt
# (create logout.txt; git add)
$ git commit -m "Add logout button"
[feature/login 0f360a4] Add logout button
 1 file changed, 1 insertion(+)
 create mode 100644 logout.txt
# (a bug in the login page: add the captcha field to login.txt; git add)
$ git commit --fixup=5631ab5
[feature/login 0e7b03c] fixup! Add login page
 1 file changed, 1 insertion(+), 1 deletion(-)
$ git log --oneline
0e7b03c (HEAD -> feature/login) fixup! Add login page
0f360a4 Add logout button
5631ab5 Add login page
8e9e4e7 (main) Add README
9316721 Add portal config
$ git rebase -i --autosquash main
# (with --autosquash the todo list already arrives arranged like this; we only save and close)
    pick 5631ab5 # Add login page
    fixup 0e7b03c # fixup! Add login page
    pick 0f360a4 # Add logout button
Successfully rebased and updated refs/heads/feature/login.
$ git log --oneline
d18169d (HEAD -> feature/login) Add logout button
4e4b6bc Add login page
8e9e4e7 (main) Add README
9316721 Add portal config
$ cat login.txt
login form: roll, password, captcha

$ git reflog -12
78f0f9a (HEAD -> feature/notice) HEAD@{0}: rebase (finish): returning to refs/heads/feature/notice
78f0f9a (HEAD -> feature/notice) HEAD@{1}: rebase (squash): Add notice dates with dd-mm-yyyy format
c07af10 HEAD@{2}: rebase (pick): Add notice dates
a665934 HEAD@{3}: rebase (reword): Add notice categories
c3fb83c HEAD@{4}: rebase (reword): Add notice categoriess
86c0eed HEAD@{5}: rebase (fixup): Add notice board
600a574 HEAD@{6}: rebase (start): checkout HEAD~6
6dadb43 HEAD@{7}: commit: Add notice categoriess
92fbb0e HEAD@{8}: commit: Debug print
8a3b36f HEAD@{9}: commit: Add date format
769758f HEAD@{10}: commit: Add notice dates
1a1ddb1 HEAD@{11}: commit: Fix typo in notice board
$ git reflog show feature/notice -3
78f0f9a (HEAD -> feature/notice) feature/notice@{0}: rebase (finish): refs/heads/feature/notice onto 8e9e4e7f6bce7ab2bb6af6e0b877c8d38156ad2d
6dadb43 feature/notice@{1}: commit: Add notice categoriess
92fbb0e feature/notice@{2}: commit: Debug print
$ git log --oneline ORIG_HEAD -7
6dadb43 Add notice categoriess
92fbb0e Debug print
8a3b36f Add date format
769758f Add notice dates
1a1ddb1 Fix typo in notice board
600a574 Add notice board
8e9e4e7 (main) Add README
$ git reset --hard ORIG_HEAD
HEAD is now at 6dadb43 Add notice categoriess
$ git log --oneline -3
6dadb43 (HEAD -> feature/notice) Add notice categoriess
92fbb0e Debug print
8a3b36f Add date format

# Way 1 (a second copy of the same repo, before any rebase): merge
$ git switch main
Already on 'main'
$ git merge --no-edit feature/gpa
Merge made by the 'ort' strategy.
 gpa.txt | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 gpa.txt
$ git log --oneline --graph
*   b1bf3a3 (HEAD -> main) Merge branch 'feature/gpa'
|\  
| * 3af94ac (feature/gpa) Show GPA on result page
| * 2e9e344 Add GPA calculator
* | 2313ddc Add contact to README
|/  
* 8e9e4e7 Add README
* 9316721 Add portal config

# Way 2 (the rebased repo above): fast-forward main
$ git switch main
Switched to branch 'main'
$ git merge --ff-only feature/gpa
Updating 2313ddc..2d52732
Fast-forward
 gpa.txt | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 gpa.txt
$ git log --oneline --graph
* 2d52732 (HEAD -> main, feature/gpa) Show GPA on result page
* 0324b2d Add GPA calculator
* 2313ddc Add contact to README
* 8e9e4e7 Add README
* 9316721 Add portal config

# (feature/sms with one commit "Add SMS alert" is already pushed; main moved on the server)
$ git fetch
From ../origin
   8e9e4e7..7c19bd3  main       -> origin/main
$ git rebase origin/main
Successfully rebased and updated refs/heads/feature/sms.
$ git push
To ../origin.git
 ! [rejected]        feature/sms -> feature/sms (non-fast-forward)
error: failed to push some refs to '../origin.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. If you want to integrate the remote changes,
hint: use 'git pull' before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
$ git push --force-with-lease
To ../origin.git
 + 96722f0...baca70f feature/sms -> feature/sms (forced update)

# (Karim, by mistake, pushed "Add SMS text" to the same feature/sms;
#  Rahim, unaware, commits "Add SMS sender name" and rebases again)
$ git push --force-with-lease
To ../origin.git
 ! [rejected]        feature/sms -> feature/sms (stale info)
error: failed to push some refs to '../origin.git'
$ git fetch
From ../origin
   baca70f..ff5f531  feature/sms -> origin/feature/sms
$ git log --oneline --graph --all
* e4a14fb (HEAD -> feature/sms) Add SMS sender name
| * ff5f531 (origin/feature/sms) Add SMS text
|/  
* baca70f Add SMS alert
* 7c19bd3 (origin/main, origin/HEAD) Show rank on result page
* 8e9e4e7 (main) Add README
* 9316721 Add portal config