feat(merge-lane)!: change no-snap to avoid fast-forward (#9159)

Until now, in case lane-b is merged into lane-a and a component (e.g.
comp-a) is ahead in lane-b, we simply updated lane-a with the new snap
of lane-b. (this behavior is similar to the "fast-forward" in Git).
This was true regardless of `--no-snap` flag. The `--no-snap` flag was
only for cases when comp-a is diverged in history and no conflicts
found, which was auto-snapping the component and saving two parents, the
head of lane-a and the head of lane-b.

In come cases, the end result of such a merge is not desirable. Some
changes might be done to this comp-a in lane-b which I would like to
investigate and test before I decide to get them in lane-a. Although
comp-a wasn't changed/snapped in my lane-a, still, I prefer to get the
changes of comp-a as modified, so then `bit diff` will show the new
changes I'm getting and then I can decide later to snap these changes.
This PR makes this possible by using the `--no-snap` flag. In practice,
it considers this state of target-ahead (lane-b) as diverged, which, as
a result - doesn't update lane-a, only the component-files and the
unmerged files with the heads data.

A new flag `--no-auto-snap` was introduced to keep the previous behavior
of `--no-snap` in case users need them.

e2e/harmony/lanes/bit-remove-on-lanes.e2e.ts

@@ -324,10 +324,10 @@ describe('bit lane command', function () {
         expect(staged).to.include(`${helper.scopes.remote}/comp2`);
       });
     });
-    describe('when merging with --no-snap', () => {
+    describe('when merging with --no-auto-snap', () => {
       before(() => {
         helper.scopeHelper.getClonedLocalScope(beforeMerge);
-        output = helper.command.mergeLane('lane-a', '-x --no-snap');
+        output = helper.command.mergeLane('lane-a', '-x --no-auto-snap');
       });
       it('bit status should not show the component as soft-removed from remote', () => {
         const status = helper.command.statusJson();

e2e/harmony/lanes/merge-lanes.e2e.ts

@@ -523,7 +523,7 @@ describe('merge lanes', function () {
     describe('merge the lane without snapping', () => {
       before(() => {
         helper.scopeHelper.getClonedLocalScope(beforeMerge);
-        helper.command.mergeLane('main', '--auto-merge-resolve theirs --no-snap -x');
+        helper.command.mergeLane('main', '--auto-merge-resolve theirs --no-auto-snap -x');
       });
       it('should show the during-merge as modified', () => {
         const status = helper.command.statusJson();
@@ -664,12 +664,12 @@ describe('merge lanes', function () {
         expect(() => helper.command.export()).to.not.throw();
       });
     });
-    describe('bit lane merge with --resolve-unrelated and --no-snap', () => {
+    describe('bit lane merge with --resolve-unrelated and --no-auto-snap', () => {
       before(() => {
         helper.scopeHelper.getClonedRemoteScope(remoteScopeAfterExport);
         helper.scopeHelper.getClonedLocalScope(afterLaneExport);
         helper.command.import();
-        helper.command.mergeLane('main', '--resolve-unrelated --no-snap');
+        helper.command.mergeLane('main', '--resolve-unrelated --no-auto-snap');
       });
       it('bit status should show the component as during-merge and staged and not everywhere else', () => {
         helper.command.expectStatusToBeClean(['componentsDuringMergeState', 'stagedComponents']);
@@ -701,7 +701,7 @@ describe('merge lanes', function () {
         helper.scopeHelper.getClonedRemoteScope(remoteScopeAfterExport);
         helper.scopeHelper.getClonedLocalScope(afterLaneExport);
         helper.command.import();
-        helper.command.mergeLane('main', '--resolve-unrelated theirs --no-snap');
+        helper.command.mergeLane('main', '--resolve-unrelated theirs --no-auto-snap');
       });
       it('bit status should show the component as during-merge and staged and not everywhere else', () => {
         helper.command.expectStatusToBeClean(['componentsDuringMergeState', 'stagedComponents']);
@@ -1063,7 +1063,7 @@ describe('merge lanes', function () {
     });
     describe('when the lane is merged to main, so currently on the FS the file exits', () => {
       before(() => {
-        helper.command.mergeLane('dev', '--no-squash --no-snap -x');
+        helper.command.mergeLane('dev', '--no-squash --no-auto-snap -x');
       });
       // previously the file was removed
       it('should not remove the file', () => {
@@ -1074,7 +1074,7 @@ describe('merge lanes', function () {
       before(() => {
         helper.scopeHelper.getClonedLocalScope(beforeMerge);
         helper.command.switchLocalLane('dev', '-x');
-        helper.command.mergeLane('main', '--no-snap -x');
+        helper.command.mergeLane('main', '--no-auto-snap -x');
       });
       // previously it was in "remain-deleted" state and the file was not created
       it('should add the file', () => {
@@ -1329,7 +1329,7 @@ describe('merge lanes', function () {
       helper.command.snapAllComponentsWithoutBuild();
       helper.command.export();
       helper.command.switchLocalLane('main', '-x');
-      mergeOutput = helper.command.mergeLane('lane-a', '-x --no-snap');
+      mergeOutput = helper.command.mergeLane('lane-a', '-x --no-auto-snap');
     });
     it('should indicate that this file was removed in the output', () => {
       expect(mergeOutput).to.have.string('removed foo.js');
@@ -1353,7 +1353,7 @@ describe('merge lanes', function () {
       helper.command.switchLocalLane('main', '-x');
       helper.command.tagAllWithoutBuild('--unmodified');
       helper.command.export();
-      mergeOutput = helper.command.mergeLane('lane-a', '-x --no-snap --no-squash');
+      mergeOutput = helper.command.mergeLane('lane-a', '-x --no-auto-snap --no-squash');
     });
     it('should indicate that this file was removed in the output', () => {
       expect(mergeOutput).to.have.string('removed foo.js');
@@ -1409,7 +1409,7 @@ describe('merge lanes', function () {
     });
     // previously it was throwing the "unrelated" error
     it('bit-lane-merge should not throw', () => {
-      expect(() => helper.command.mergeLane('main', '-x --no-snap')).to.not.throw();
+      expect(() => helper.command.mergeLane('main', '-x --no-auto-snap')).to.not.throw();
     });
   });
   describe('renaming files from uppercase to lowercase', () => {
@@ -1629,4 +1629,63 @@ describe('merge lanes', function () {
       expect(comp1.head).to.equal(oldSnapComp1);
     });
   });
+  describe('--no-snap vs --no-auto-snap', () => {
+    let beforeMerge: string;
+    let snapLaneA: string;
+    let snapLaneB: string;
+    before(() => {
+      helper.scopeHelper.setNewLocalAndRemoteScopes();
+      helper.command.createLane('lane-a');
+      helper.fixtures.populateComponents(1);
+      helper.command.snapAllComponentsWithoutBuild();
+      snapLaneA = helper.command.getHeadOfLane('lane-a', 'comp1');
+      helper.command.export();
+      helper.command.createLane('lane-b');
+      helper.fixtures.populateComponents(1, undefined, 'from-lane-b');
+      helper.command.snapAllComponentsWithoutBuild();
+      snapLaneB = helper.command.getHeadOfLane('lane-b', 'comp1');
+      helper.command.export();
+      helper.command.switchLocalLane('lane-a', '-x');
+      beforeMerge = helper.scopeHelper.cloneLocalScope();
+    });
+    describe('with --no-auto-snap', () => {
+      before(() => {
+        helper.command.mergeLane('lane-b', '--no-auto-snap -x');
+      });
+      it('should update current lane according to the merged one', () => {
+        const snap = helper.command.getHeadOfLane('lane-a', 'comp1');
+        expect(snap).to.equal(snapLaneB);
+      });
+      it('should not leave the components as modified', () => {
+        const status = helper.command.statusJson();
+        expect(status.modifiedComponents).to.have.lengthOf(0);
+      });
+    });
+    describe('with --no-snap', () => {
+      before(() => {
+        helper.scopeHelper.getClonedLocalScope(beforeMerge);
+        helper.command.mergeLane('lane-b', '--no-snap -x');
+      });
+      it('should not update current lane according to the merged one', () => {
+        const snap = helper.command.getHeadOfLane('lane-a', 'comp1');
+        expect(snap).to.not.equal(snapLaneB);
+        expect(snap).to.equal(snapLaneA);
+      });
+      it('should leave the components as modified', () => {
+        const status = helper.command.statusJson();
+        expect(status.modifiedComponents).to.have.lengthOf(1);
+      });
+      describe('after snapping', () => {
+        before(() => {
+          helper.command.snapAllComponentsWithoutBuild();
+        });
+        it('should save two parents, from the current lane and from the merged lane', () => {
+          const versionObj = helper.command.catComponent('comp1@latest');
+          expect(versionObj.parents).to.have.lengthOf(2);
+          expect(versionObj.parents[0]).to.equal(snapLaneA);
+          expect(versionObj.parents[1]).to.equal(snapLaneB);
+        });
+      });
+    });
+  });
 });

e2e/harmony/merge-config.e2e.ts

@@ -123,7 +123,10 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.getClonedLocalScope(mainBeforeDiverge);
       helper.command.snapAllComponentsWithoutBuild('--unmodified');
       helper.command.export();
-      helper.command.mergeLane(`${helper.scopes.remote}/dev`, '--no-snap --skip-dependency-installation --no-squash');
+      helper.command.mergeLane(
+        `${helper.scopes.remote}/dev`,
+        '--no-auto-snap --skip-dependency-installation --no-squash'
+      );
     });
     it('bit status should not show the component with an issue of MergeConfigHasConflict', () => {
       helper.command.expectStatusToNotHaveIssue(IssuesClasses.MergeConfigHasConflict.name);
@@ -163,7 +166,7 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.reInitLocalScope();
       helper.scopeHelper.addRemoteScope();
       helper.command.importLane('dev');
-      helper.command.mergeLane('main', '--no-snap --skip-dependency-installation');
+      helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation');
       beforeConfigResolved = helper.scopeHelper.cloneLocalScope();
     });
     it('bit status should show the component with an issue of MergeConfigHasConflict', () => {
@@ -230,7 +233,7 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.addRemoteScope();
       helper.command.importLane('dev', '--skip-dependency-installation');
       beforeMerge = helper.scopeHelper.cloneLocalScope();
-      helper.command.mergeLane('main', '--no-snap --skip-dependency-installation');
+      helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation');
       beforeConfigResolved = helper.scopeHelper.cloneLocalScope();
     });
     it('bit status should show the component with an issue of MergeConfigHasConflict', () => {
@@ -267,7 +270,7 @@ describe('merge config scenarios', function () {
     describe('merging with --auto-merge-resolve ours', () => {
       before(() => {
         helper.scopeHelper.getClonedLocalScope(beforeMerge);
-        helper.command.mergeLane('main', '--no-snap --skip-dependency-installation --auto-merge-resolve=ours');
+        helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation --auto-merge-resolve=ours');
       });
       it('should not generate the config-merge file', () => {
         const configMerge = helper.general.getConfigMergePath();
@@ -283,7 +286,7 @@ describe('merge config scenarios', function () {
     describe('merging with --auto-merge-resolve theirs', () => {
       before(() => {
         helper.scopeHelper.getClonedLocalScope(beforeMerge);
-        helper.command.mergeLane('main', '--no-snap --skip-dependency-installation --auto-merge-resolve=theirs');
+        helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation --auto-merge-resolve=theirs');
       });
       it('should not generate the config-merge file', () => {
         const configMerge = helper.general.getConfigMergePath();
@@ -315,7 +318,7 @@ describe('merge config scenarios', function () {
       helper.command.snapAllComponentsWithoutBuild('--unmodified');
       helper.command.export();
 
-      helper.command.mergeLane('dev', '--no-snap -x --no-squash');
+      helper.command.mergeLane('dev', '--no-auto-snap -x --no-squash');
     });
     // previously, it was ignoring the previous config and only adding "ramda".
     it('should not remove the packages it had previously via deps set', () => {
@@ -350,7 +353,7 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.reInitLocalScope();
       helper.scopeHelper.addRemoteScope();
       helper.command.importLane('dev', '--skip-dependency-installation');
-      helper.command.mergeLane('main', '--no-snap --skip-dependency-installation --ignore-config-changes');
+      helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation --ignore-config-changes');
       beforeConfigResolved = helper.scopeHelper.cloneLocalScope();
     });
     it('bit status should show the component with an issue of MergeConfigHasConflict', () => {
@@ -417,7 +420,7 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.reInitLocalScope();
       helper.scopeHelper.addRemoteScope();
       helper.command.importLane('dev', '--skip-dependency-installation');
-      helper.command.mergeLane('main', '--no-snap --skip-dependency-installation');
+      helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation');
       beforeConfigResolved = helper.scopeHelper.cloneLocalScope();
     });
     it('bit status should show the component with an issue of MergeConfigHasConflict', () => {
@@ -537,7 +540,7 @@ describe('merge config scenarios', function () {
       describe('when the dep was updated on the lane only, not on main', () => {
         describe('when the dep is in workspace.jsonc', () => {
           before(() => {
-            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-snap`);
+            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-auto-snap`);
           });
           it('should change workspace.jsonc with the updated dependency', () => {
             const policy = helper.workspaceJsonc.getPolicyFromDependencyResolver();
@@ -548,7 +551,7 @@ describe('merge config scenarios', function () {
           before(() => {
             helper.scopeHelper.getClonedLocalScope(beforeMerges);
             helper.workspaceJsonc.addPolicyToDependencyResolver({ dependencies: {} });
-            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-snap`);
+            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-auto-snap`);
           });
           it('should auto-update the dependency according to the lane, because only there it was changed', () => {
             const deps = helper.command.getCompDepsIdsFromData('comp1');
@@ -583,7 +586,7 @@ describe('merge config scenarios', function () {
         });
         describe('when the dep is in workspace.jsonc', () => {
           before(() => {
-            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-snap`);
+            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-auto-snap`);
           });
           it('should not write config-merge file', () => {
             const conflictFile = helper.general.getConfigMergePath();
@@ -605,7 +608,7 @@ describe('merge config scenarios', function () {
           before(() => {
             helper.scopeHelper.getClonedLocalScope(afterExport);
             helper.workspaceJsonc.addPolicyToDependencyResolver({ dependencies: {} });
-            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-snap`);
+            helper.command.mergeLane(`${helper.scopes.remote}/dev --no-squash --no-auto-snap`);
           });
           it('bit status should not show a workspace issue', () => {
             const status = helper.command.statusJson();
@@ -681,7 +684,7 @@ describe('merge config scenarios', function () {
           let mergeOutput: string;
           before(() => {
             helper.scopeHelper.getClonedLocalScope(laneWs);
-            mergeOutput = helper.command.mergeLane(`main --no-snap -x`);
+            mergeOutput = helper.command.mergeLane(`main --no-auto-snap -x`);
           });
           it('should not update workspace.jsonc', () => {
             const policy = helper.workspaceJsonc.getPolicyFromDependencyResolver();
@@ -723,7 +726,7 @@ describe('merge config scenarios', function () {
       helper.scopeHelper.reInitLocalScope();
       helper.scopeHelper.addRemoteScope();
       helper.command.importLane('dev', '--skip-dependency-installation');
-      helper.command.mergeLane('main', '--no-snap --skip-dependency-installation --ignore-config-changes');
+      helper.command.mergeLane('main', '--no-auto-snap --skip-dependency-installation --ignore-config-changes');
     });
     it('should not delete the previously deps set', () => {
       const deps = helper.command.getCompDepsIdsFromData('comp1');

e2e/harmony/updates-from-main-and-lane.e2e.ts

@@ -68,7 +68,7 @@ describe('updates from main and lane', function () {
       before(() => {
         mergeOutput = helper.command.mergeLane(
           'main',
-          '--skip-dependency-installation --no-snap --include-non-lane-comps'
+          '--skip-dependency-installation --no-auto-snap --include-non-lane-comps'
         );
       });
       it('should update not only components belong to the main but also components that are available on the workspace and have updates from main', () => {

scopes/component/merging/merge-status-provider.ts

@@ -22,6 +22,7 @@ export type MergeStatusProviderOptions = {
   mergeStrategy: MergeStrategy;
   ignoreConfigChanges?: boolean;
   shouldSquash?: boolean;
+  handleTargetAheadAsDiverged?: boolean;
 };
 
 export const compIsAlreadyMergedMsg = 'component is already merged';
@@ -305,7 +306,12 @@ other:   ${otherLaneHead.toString()}`);
         // component is ahead nothing to merge.
         return this.returnUnmerged(id, compIsAlreadyMergedMsg, true);
       }
-      if (divergeData.isTargetAhead()) {
+      if (!divergeData.isTargetAhead()) {
+        // we know that localHead and remoteHead are set, so if none of them is ahead they must be equal
+        return this.returnUnmerged(id, compIsAlreadyMergedMsg, true);
+      }
+      // target is ahead.
+      if (!this.options.handleTargetAheadAsDiverged) {
         // just override with the model data
         return {
           ...componentStatus,
@@ -314,8 +320,7 @@ other:   ${otherLaneHead.toString()}`);
           divergeData,
         };
       }
-      // we know that localHead and remoteHead are set, so if none of them is ahead they must be equal
-      return this.returnUnmerged(id, compIsAlreadyMergedMsg, true);
+      // target is ahead and we want to treat it as diverged, continue.
     }
 
     // it's diverged and needs merge operation

scopes/component/merging/merging.main.runtime.ts

@@ -130,7 +130,7 @@ export class MergingMain {
     mergeStrategy: MergeStrategy,
     abort: boolean,
     resolve: boolean,
-    noSnap: boolean,
+    noAutoSnap: boolean,
     message: string,
     build: boolean,
     skipDependencyInstallation: boolean
@@ -148,7 +148,7 @@ export class MergingMain {
         consumer,
         bitIds,
         mergeStrategy,
-        noSnap,
+        noAutoSnap,
         message,
         build,
         skipDependencyInstallation
@@ -166,7 +166,7 @@ export class MergingMain {
     consumer: Consumer,
     bitIds: ComponentID[],
     mergeStrategy: MergeStrategy,
-    noSnap: boolean,
+    noAutoSnap: boolean,
     snapMessage: string,
     build: boolean,
     skipDependencyInstallation: boolean
@@ -195,7 +195,7 @@ export class MergingMain {
       allComponentsStatus,
       otherLaneId: currentLaneId,
       currentLane: currentLaneObject,
-      noSnap,
+      noAutoSnap: noAutoSnap,
       snapMessage,
       build,
       skipDependencyInstallation,
@@ -210,6 +210,7 @@ export class MergingMain {
     allComponentsStatus,
     otherLaneId,
     currentLane,
+    noAutoSnap,
     noSnap,
     tag,
     snapMessage,
@@ -220,6 +221,7 @@ export class MergingMain {
     allComponentsStatus: ComponentMergeStatus[];
     otherLaneId: LaneId;
     currentLane?: Lane;
+    noAutoSnap?: boolean;
     noSnap?: boolean;
     tag?: boolean;
     snapMessage?: string;
@@ -309,7 +311,7 @@ export class MergingMain {
     const getSnapOrTagResults = async (): Promise<MergeSnapResults> => {
       // if one of the component has conflict, don't snap-merge. otherwise, some of the components would be snap-merged
       // and some not. besides the fact that it could by mistake tag dependent, it's a confusing state. better not snap.
-      if (noSnap || leftUnresolvedConflicts || componentsHasConfigMergeConflicts) {
+      if (noAutoSnap || noSnap || leftUnresolvedConflicts || componentsHasConfigMergeConflicts) {
         return null;
       }
       if (tag) {