Changing references of lightning master to main (#1356)

**Context:**
The default branch of pennylane-lightning will be changed from `master`
to `main`. The references to `master` need to be updated.

**Description of the Change:**
Change references of `master` to `main`

**Benefits:**
The default branch gets updated.

**Possible Drawbacks:**
None

**Related GitHub Issues:**

---------

Co-authored-by: ringo-but-quantum <github-ringo-but-quantum@xanadu.ai>

Author: runora95

.github/CHANGELOG.md

@@ -35,6 +35,9 @@
 
 <h3>Internal changes ⚙️</h3>
 
+- Change default branch references from `master` to `main`.
+  [(#1356)](https://github.com/PennyLaneAI/pennylane-lightning/pull/1356)
+
 - Upgrade CIs to use CUDA 12.9.
   [(#1353)](https://github.com/PennyLaneAI/pennylane-lightning/pull/1353)
   [(#1354)](https://github.com/PennyLaneAI/pennylane-lightning/pull/1354)

.github/workflows/changelog_reminder.yml

@@ -16,7 +16,7 @@ jobs:
         changelog_regex: '.github/CHANGELOG.md'
         customPrMessage: |
           Hello. You may have forgotten to update the changelog!
-          Please edit [.github/CHANGELOG.md](/PennyLaneAI/pennylane-lightning/blob/master/.github/CHANGELOG.md) with:
+          Please edit [.github/CHANGELOG.md](/PennyLaneAI/pennylane-lightning/blob/main/.github/CHANGELOG.md) with:
           * A one-to-two sentence description of the change. You may include a small working example for new features.
           * A link back to this PR.
           * Your name (or GitHub username) in the contributors section.

.github/workflows/code_security_scan.yml

@@ -3,7 +3,7 @@ on:
   pull_request:
   push:
     branches:
-      - master
+      - main
 
 concurrency:
   group: code-security-scan-${{ github.workflow }}-${{ github.ref }}
@@ -25,4 +25,3 @@ jobs:
       semgrep-error-on-impact: HIGH
       semgrep-error-on-severity: ERROR
       bandit-error-on-severity: HIGH
-

.github/workflows/compat-docker-latest.yml

@@ -14,7 +14,7 @@ jobs:
     name: Docker latest - Linux::x86_64
     uses: ./.github/workflows/docker_linux_x86_64.yml
     with:
-      lightning-version: master
+      lightning-version: main
       pennylane-version: main
       push-to-dockerhub: false
     secrets: inherit # pass all secrets

.github/workflows/dev_version_script.py

@@ -83,15 +83,15 @@ def update_prerelease_version(repo_root_path: Path, version: Version):
     parser = argparse.ArgumentParser()
     parser.add_argument("--pr-path", dest="pr", type=Path, required=True, help="Path to the PR dir")
     parser.add_argument(
-        "--master-path", dest="master", type=Path, required=True, help="Path to the master dir"
+        "--main-path", dest="main", type=Path, required=True, help="Path to the main dir"
     )
 
     args = parser.parse_args()
 
     pr_version = extract_version(args.pr)
-    master_version = extract_version(args.master)
+    main_version = extract_version(args.main)
 
-    print("Got Package Version from 'master' ->", str(master_version))
+    print("Got Package Version from 'main' ->", str(main_version))
     print("Got Package Version from 'PR' ->", str(pr_version))
 
     # Only attempt to bump the version if the pull_request is:
@@ -102,7 +102,7 @@ def update_prerelease_version(repo_root_path: Path, version: Version):
     #  This captures the case during release where we might bump the release version
     #  within a PR and reset tag back to dev0
     if (
-        pr_version > master_version
+        pr_version > main_version
         and pr_version.prerelease
         and pr_version.prerelease == DEV_PRERELEASE_TAG_START
     ):
@@ -111,22 +111,22 @@ def update_prerelease_version(repo_root_path: Path, version: Version):
         )
         print("If this is happening in error, please report it to the PennyLane team!")
     elif pr_version.prerelease and pr_version.prerelease.startswith(DEV_PRERELEASE_TAG_PREFIX):
-        # If master branch does not have a prerelease (for any reason) OR does not have an ending number
+        # If main branch does not have a prerelease (for any reason) OR does not have an ending number
         # Then default to the starting tag
-        if not master_version.prerelease or master_version.prerelease == DEV_PRERELEASE_TAG_PREFIX:
+        if not main_version.prerelease or main_version.prerelease == DEV_PRERELEASE_TAG_PREFIX:
             next_prerelease_version = DEV_PRERELEASE_TAG_START
         else:
-            # If master branch does not have a prerelease (for any reason) OR does not have an ending number
+            # If main branch does not have a prerelease (for any reason) OR does not have an ending number
             # Then default to the starting tag
             if (
-                not master_version.prerelease
-                or master_version.prerelease == DEV_PRERELEASE_TAG_PREFIX
+                not main_version.prerelease
+                or main_version.prerelease == DEV_PRERELEASE_TAG_PREFIX
             ):
                 next_prerelease_version = DEV_PRERELEASE_TAG_START
             else:
-                # Generate the next prerelease version (eg: dev1 -> dev2). Sourcing from master version.
-                next_prerelease_version = master_version.next_version("prerelease").prerelease
-            new_version = master_version.replace(prerelease=next_prerelease_version)
+                # Generate the next prerelease version (eg: dev1 -> dev2). Sourcing from main version.
+                next_prerelease_version = main_version.next_version("prerelease").prerelease
+            new_version = main_version.replace(prerelease=next_prerelease_version)
             if pr_version != new_version:
                 print(f"Updating PR package version from -> '{pr_version}', to -> {new_version}")
                 update_prerelease_version(args.pr, new_version)

.github/workflows/format.yml

@@ -3,7 +3,7 @@ on:
   pull_request:
   push:
     branches:
-      - master
+      - main
 
 concurrency:
   group: format-${{ github.ref }}

.github/workflows/pre_release_version_bump.yml

@@ -35,4 +35,4 @@ jobs:
           body: updated changelog and _version.py
           branch: pre-release-version-bump
           reviewers: tomlqc, maliasadi
-          base: master
+          base: main

.github/workflows/sync-main-to-master.yml

@@ -0,0 +1,53 @@
+# This workflow syncs the main branch to master every weekday. It will remain until the master branch is deleted.
+name: Sync main to master
+
+on:
+  # Scheduled trigger every weekday at 2:47am UTC
+  schedule:
+  - cron:  '47 2 * * 1-5'
+  workflow_dispatch:
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          ref: master
+          token: ${{ secrets.PENNYLANE_MASTER_MAIN_WRITE }}
+          fetch-depth: 0 
+
+      - name: Sync main to master
+        run: |
+          git fetch origin 
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"          
+          if git merge --no-commit --ff-only origin/main; then
+            echo "Synching from main to master."
+            echo "merge_conflict=false" >> $GITHUB_ENV
+            git push origin master 
+          else
+            echo "Merge conflict detected. Creating a PR ..."
+            echo "merge_conflict=true" >> $GITHUB_ENV
+            git merge --abort || true 
+          fi   
+
+        # If there are conflicts, create a PR for resolution
+      - name: Create PR for conflict resolution
+        env:
+          GH_TOKEN: ${{ secrets.PENNYLANE_MASTER_MAIN_WRITE }}
+        if: env.merge_conflict == 'true'            
+        run: |
+          git checkout main
+          BRANCH="main_$(date +'%Y-%m-%d-%H-%M-%S')"
+          echo "tmp_branch=$BRANCH" >> $GITHUB_ENV
+          git checkout -b "$BRANCH"
+          git config user.name "GitHub Actions Bot"
+          git config user.email "<>"
+          if ! git diff --quiet origin/master origin/main; then
+            git push --set-upstream origin "$BRANCH"
+            gh pr create --repo PennyLaneAI/pennylane-lightning --title "Daily main sync to master - conflict resolution" --body "" --base master 
+          else
+            echo "No new changes to sync from main to master."
+          fi 
+          exit 1

.github/workflows/tests_gpu_cpp.yml

@@ -5,11 +5,11 @@ on:
       lightning-version:
         type: string
         required: true
-        description: The version of Lightning to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from master)
+        description: The version of Lightning to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from main)
       pennylane-version:
         type: string
         required: true
-        description: The version of PennyLane to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from master)
+        description: The version of PennyLane to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from main)
   pull_request:
     types:
       - opened
@@ -18,7 +18,7 @@ on:
       - ready_for_review
   push:
     branches:
-      - master
+      - main
 
 env:
   CI_CUDA_ARCH: 86

.github/workflows/tests_gpu_python.yml

@@ -5,11 +5,11 @@ on:
       lightning-version:
         type: string
         required: true
-        description: The version of Lightning to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from master)
+        description: The version of Lightning to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from main)
       pennylane-version:
         type: string
         required: true
-        description: The version of PennyLane to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from master)
+        description: The version of PennyLane to use. Valid values are either 'release' (most recent release candidate), 'stable' (most recent git-tag) or 'latest' (most recent commit from main)
   pull_request:
     types:
       - opened
@@ -18,7 +18,7 @@ on:
       - ready_for_review
   push:
     branches:
-      - master
+      - main
 
 env:
   CI_CUDA_ARCH: 86