feat(git): allow custom merge commit ids

Currently, merge commits can have a git tag, but they cannot have a
custom git commit ID.

This commit allows modifying the default merge commit id.
It also displays all merge commits IDs, which undoes
3ccf027f42

src/diagrams/git/gitGraphParserV2.spec.js

@@ -496,6 +496,76 @@ describe('when parsing a gitGraph', function () {
     ]);
   });
 
+  it('should handle merge ids', function () {
+    const str = `gitGraph:
+      commit
+      branch testBranch
+      checkout testBranch
+      commit
+      checkout main
+      %% Merge Tag and ID
+      merge testBranch tag: "merge-tag" id: "2-222"
+      branch testBranch2
+      checkout testBranch2
+      commit
+      checkout main
+      %% Merge ID and Tag (reverse order)
+      merge testBranch2 id: "4-444" tag: "merge-tag2"
+      branch testBranch3
+      checkout testBranch3
+      commit
+      checkout main
+      %% just Merge ID
+      merge testBranch3 id: "6-666"
+    `;
+
+    parser.parse(str);
+    const commits = parser.yy.getCommits();
+    expect(Object.keys(commits).length).toBe(7);
+    expect(parser.yy.getCurrentBranch()).toBe('main');
+    expect(parser.yy.getDirection()).toBe('LR');
+
+    // The order of these commits is in alphabetical order of IDs
+    const [
+      mainCommit,
+      testBranchCommit,
+      testBranchMerge,
+      testBranch2Commit,
+      testBranch2Merge,
+      testBranch3Commit,
+      testBranch3Merge,
+    ] = Object.values(commits);
+
+    console.log(Object.keys(commits));
+
+    expect(mainCommit.branch).toBe('main');
+    expect(mainCommit.parents).toStrictEqual([]);
+
+    expect(testBranchCommit.branch).toBe('testBranch');
+    expect(testBranchCommit.parents).toStrictEqual([mainCommit.id]);
+
+    expect(testBranchMerge.branch).toBe('main');
+    expect(testBranchMerge.parents).toStrictEqual([mainCommit.id, testBranchCommit.id]);
+    expect(testBranchMerge.tag).toBe('merge-tag');
+    expect(testBranchMerge.id).toBe('2-222');
+
+    expect(testBranch2Merge.branch).toBe('main');
+    expect(testBranch2Merge.parents).toStrictEqual([testBranchMerge.id, testBranch2Commit.id]);
+    expect(testBranch2Merge.tag).toBe('merge-tag2');
+    expect(testBranch2Merge.id).toBe('4-444');
+
+    expect(testBranch3Merge.branch).toBe('main');
+    expect(testBranch3Merge.parents).toStrictEqual([testBranch2Merge.id, testBranch3Commit.id]);
+    expect(testBranch3Merge.id).toBe('6-666');
+
+    expect(parser.yy.getBranchesAsObjArray()).toStrictEqual([
+      { name: 'main' },
+      { name: 'testBranch' },
+      { name: 'testBranch2' },
+      { name: 'testBranch3' },
+    ]);
+  });
+
   it('should throw error when try to branch existing branch: main', function () {
     const str = `gitGraph
     commit