Implement exercise T6L2/branch-forward

branch_forward/.gitmastery-exercise.json

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+{
+  "exercise_name": "branch-forward",
+  "tags": [
+    "git-branch",
+    "git-merge"
+  ],
+  "requires_git": true,
+  "requires_github": false,
+  "base_files": {},
+  "exercise_repo": {
+    "repo_type": "local",
+    "repo_name": "love-story",
+    "repo_title": null,
+    "create_fork": null,
+    "init": true
+  }
+}

branch_forward/README.md

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+# branch-forward
+
+You are outlining a story and experimenting with different plotlines. Each version lives on its own branch, and you now need to fold the right storyline back into `main` without cluttering the history.
+
+## Learning objectives
+
+- Identify when a branch can be fast-forward merged
+- Use fast-forward merges to keep the commit graph linear
+- [Fast-forward merges](https://nus-cs2103-ay2526s1.github.io/website/book/gitAndGithub/merge/index.html)
+
+## Task
+
+1. Review the `with-sally` and `with-ginny` branches.
+2. Merge only the branch(es) that can be fast-forwarded into `main`.
+3. Leave other branches (if any) unmerged.
+
+## Hints
+
+
+<details>
+
+<summary>Hint 1</summary>
+
+Ensure you have switched to the destination branch before initiating the merge.
+
+</details>

branch_forward/download.py

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+from exercise_utils.file import append_to_file, create_or_update_file
+from exercise_utils.git import add, checkout, commit
+
+
+def setup(verbose: bool = False):
+    create_or_update_file(
+        "story.txt",
+        """
+        Harry was single.
+        """,
+    )
+    add(["story.txt"], verbose)
+    commit("Introduce Harry", verbose)
+
+    append_to_file(
+        "story.txt",
+        """
+        Harry did not have a family.
+        """,
+    )
+    add(["story.txt"], verbose)
+    commit("Add about family", verbose)
+
+    checkout("with-ginny", True, verbose)
+    append_to_file(
+        "story.txt",
+        """
+        Then he met Ginny.
+        """,
+    )
+    add(["story.txt"], verbose)
+    commit("Add about Ginny", verbose)
+
+    checkout("main", False, verbose)
+    create_or_update_file(
+        "cast.txt",
+        """
+        Harry
+        """,
+    )
+    add(["cast.txt"], verbose)
+    commit("Add cast.txt", verbose)
+
+    checkout("with-sally", True, verbose)
+    append_to_file(
+        "story.txt",
+        """
+        Then he met Sally
+        """,
+    )
+    add(["story.txt"], verbose)
+    commit("Mention Sally", verbose)
+
+    checkout("with-ginny", False, verbose)
+    append_to_file(
+        "story.txt",
+        """
+        Ginny was single too
+        """,
+    )
+    add(["story.txt"], verbose)
+    commit("Mention Ginny is single", verbose)
+

branch_forward/tests/specs/base.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+    - type: merge
+      branch-name: with-sally
+

branch_forward/tests/specs/merge_with_sally_no_ff.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+    - type: merge
+      branch-name: with-sally
+      no-ff: true
+

branch_forward/tests/specs/no_merges.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+

branch_forward/tests/specs/other_branch_ff.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: with-ron
+    - type: checkout
+      branch-name: with-ron
+    - type: commit
+      empty: true
+      message: Mention Ron
+
+    - type: checkout
+      branch-name: main
+    - type: merge
+      branch-name: with-ron
+

branch_forward/tests/specs/other_branch_non_ff.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+    - type: merge
+      branch-name: with-ginny
+

branch_forward/tests/specs/with_sally_non_ff_then_ff.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Introduce Harry
+      id: start
+    - type: commit
+      empty: true
+      message: Add about family
+
+    - type: branch
+      branch-name: with-ginny
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Add about Ginny
+
+    - type: checkout
+      branch-name: main
+    - type: commit
+      empty: true
+      message: Add cast.txt
+
+    - type: branch
+      branch-name: with-sally
+    - type: checkout
+      branch-name: with-sally
+    - type: commit
+      empty: true
+      message: Mention Sally
+
+    - type: checkout
+      branch-name: with-ginny
+    - type: commit
+      empty: true
+      message: Mention Ginny is single
+
+    - type: checkout
+      branch-name: main
+    - type: bash
+      runs: |
+        git merge with-sally --no-ff -m "Non fast-forward merge"
+        git reset --hard 'HEAD^'
+        git merge with-sally
+