Implement exercise T6L2/merge-undo

merge_undo/.gitmastery-exercise.json

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+{
+  "exercise_name": "merge-undo",
+  "tags": [
+    "git-branch",
+    "git-merge",
+    "git-reset"
+  ],
+  "requires_git": true,
+  "requires_github": false,
+  "base_files": {},
+  "exercise_repo": {
+    "repo_type": "local",
+    "repo_name": "play-characters",
+    "repo_title": null,
+    "create_fork": null,
+    "init": true
+  }
+}

merge_undo/README.md

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+# merge-undo
+
+Scenario: You are keeping notes on the characters of a play that you are writing. In the main story line (which is in the `main` branch), you introduced two characters, Rick and Morty. You had two other characters in two separate branches `daughter` and `son-in-law`. Just now, you introduced these two characters to the main story line by merging the two branches to the `main` branch.
+
+```mermaid
+gitGraph
+    commit id: "Add Rick"
+    commit id: "Add morty"
+    branch daughter
+    branch son-in-law
+    checkout daughter
+    commit id: "Add Beth"
+    checkout son-in-law
+    commit id: "Add Jerry"
+    checkout main
+    commit id: "Mention Morty is grandson"
+    merge daughter id: "Introduce Beth"
+    merge son-in-law id: "Introduce Jerry"
+```
+
+However, now you realise this is premature, and wish to undo that change.
+
+## Task
+
+Undo the merging of branches `son-in-law` and `daughter`.
+
+The result should be as follows:
+
+```mermaid
+gitGraph
+    commit id: "Add Rick"
+    commit id: "Add morty"
+    branch daughter
+    branch son-in-law
+    checkout daughter
+    commit id: "Add Beth"
+    checkout son-in-law
+    commit id: "Add Jerry"
+    checkout main
+    commit id: "Mention Morty is grandson"
+```

merge_undo/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, merge_with_message
+
+
+def setup(verbose: bool = False):
+    create_or_update_file(
+        "rick.txt",
+        """
+        Scientist
+        """,
+    )
+    add(["rick.txt"], verbose)
+    commit("Add Rick", verbose)
+
+    create_or_update_file(
+        "morty.txt",
+        """
+        Boy
+        """,
+    )
+    add(["morty.txt"], verbose)
+    commit("Add morty", verbose)
+
+    checkout("daughter", True, verbose)
+    create_or_update_file(
+        "beth.txt",
+        """
+        Vet
+        """,
+    )
+    add(["beth.txt"], verbose)
+    commit("Add Beth", verbose)
+
+    checkout("main", False, verbose)
+
+    checkout("son-in-law", True, verbose)
+    create_or_update_file(
+        "jerry.txt",
+        """
+        Salesman
+        """,
+    )
+    add(["jerry.txt"], verbose)
+    commit("Add Jerry", verbose)
+
+    checkout("main", False, verbose)
+    append_to_file(
+        "morty.txt",
+        """
+        Grandson
+        """,
+    )
+    add(["morty.txt"], verbose)
+    commit("Mention Morty is grandson", verbose)
+
+    merge_with_message("daughter", True, "Introduce Beth", verbose)
+    merge_with_message("son-in-law", True, "Introduce Jerry", verbose)

merge_undo/tests/specs/base.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Empty commit
+      id: start
+
+    # Add rick.txt and commit
+    - type: new-file
+      filename: rick.txt
+      contents: Scientist
+    - type: commit
+      message: Add Rick
+
+    # Add morty.txt and commit
+    - type: new-file
+      filename: morty.txt
+      contents: Boy
+    - type: commit
+      message: Add morty
+      id: morty-initial-commit
+
+    # Create 'daughter' branch, add beth.txt and commit
+    - type: branch
+      branch-name: daughter
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: daughter
+    - type: new-file
+      filename: beth.txt
+      contents: Vet
+    - type: commit
+      message: Add Beth
+
+    # Create 'son-in-law' branch, add jerry.txt and commit
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: son-in-law
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: son-in-law
+    - type: new-file
+      filename: jerry.txt
+      contents: Salesman
+    - type: commit
+      message: Add Jerry
+
+    # Checkout back to main, edit morty.txt and commit.
+    - type: checkout
+      branch-name: main
+    - type: edit-file
+      filename: morty.txt
+      contents: |
+        Boy
+        Grandson
+    - type: commit
+      message: Mention Morty is grandson
+      id: final-main-commit
+

merge_undo/tests/specs/detached_head.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Empty commit
+      id: start
+    - type: new-file
+      filename: rick.txt
+      contents: Scientist
+    - type: commit
+      message: Add Rick
+    - type: new-file
+      filename: morty.txt
+      contents: Boy
+    - type: commit
+      message: Add morty
+      id: morty-initial-commit
+    - type: branch
+      branch-name: daughter
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: daughter
+    - type: new-file
+      filename: beth.txt
+      contents: Vet
+    - type: commit
+      message: Add Beth
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: son-in-law
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: son-in-law
+    - type: new-file
+      filename: jerry.txt
+      contents: Salesman
+    - type: commit
+      message: Add Jerry
+    - type: checkout
+      branch-name: main
+    - type: edit-file
+      filename: morty.txt
+      contents: |
+        Boy
+        Grandson
+    - type: commit
+      message: Mention Morty is grandson
+    - type: checkout
+      commit-hash: main
+

merge_undo/tests/specs/main_wrong_commit.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Empty commit
+      id: start
+    - type: new-file
+      filename: rick.txt
+      contents: Scientist
+    - type: commit
+      message: Add Rick
+    - type: new-file
+      filename: morty.txt
+      contents: Boy
+    - type: commit
+      message: Add morty
+      id: morty-initial-commit
+    - type: branch
+      branch-name: daughter
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: daughter
+    - type: new-file
+      filename: beth.txt
+      contents: Vet
+    - type: commit
+      message: Add Beth
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: son-in-law
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: son-in-law
+    - type: new-file
+      filename: jerry.txt
+      contents: Salesman
+    - type: commit
+      message: Add Jerry
+    - type: checkout
+      branch-name: main
+

merge_undo/tests/specs/merges_not_undone.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Empty commit
+      id: start
+    - type: new-file
+      filename: rick.txt
+      contents: Scientist
+    - type: commit
+      message: Add Rick
+    - type: new-file
+      filename: morty.txt
+      contents: Boy
+    - type: commit
+      message: Add morty
+      id: morty-initial-commit
+    - type: branch
+      branch-name: daughter
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: daughter
+    - type: new-file
+      filename: beth.txt
+      contents: Vet
+    - type: commit
+      message: Add Beth
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: son-in-law
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: son-in-law
+    - type: new-file
+      filename: jerry.txt
+      contents: Salesman
+    - type: commit
+      message: Add Jerry
+    - type: checkout
+      branch-name: main
+    - type: edit-file
+      filename: morty.txt
+      contents: |
+        Boy
+        Grandson
+    - type: commit
+      message: Mention Morty is grandson
+    - type: merge
+      branch-name: daughter
+      message: Introduce Beth
+      no-ff: true
+    - type: merge
+      branch-name: son-in-law
+      message: introduce Jerry
+      no-ff: true

merge_undo/tests/specs/not_main.yml

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+initialization:
+  steps:
+    - type: commit
+      empty: true
+      message: Empty commit
+      id: start
+    - type: new-file
+      filename: rick.txt
+      contents: Scientist
+    - type: commit
+      message: Add Rick
+    - type: new-file
+      filename: morty.txt
+      contents: Boy
+    - type: commit
+      message: Add morty
+      id: morty-initial-commit
+    - type: branch
+      branch-name: daughter
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: daughter
+    - type: new-file
+      filename: beth.txt
+      contents: Vet
+    - type: commit
+      message: Add Beth
+    - type: checkout
+      branch-name: main
+    - type: branch
+      branch-name: son-in-law
+      from-commit: morty-initial-commit
+    - type: checkout
+      branch-name: son-in-law
+    - type: new-file
+      filename: jerry.txt
+      contents: Salesman
+    - type: commit
+      message: Add Jerry
+    - type: checkout
+      branch-name: main
+    - type: edit-file
+      filename: morty.txt
+      contents: |
+        Boy
+        Grandson
+    - type: commit
+      message: Mention Morty is grandson
+    - type: checkout
+      branch-name: daughter