Fixing an edge case in lockdiff where all the projects may be removed…

… from the lock file.

gps/verify/lockdiff.go

@@ -95,26 +95,31 @@ func DiffLocks(l1, l2 gps.Lock) LockDelta {
 			Name: pr1,
 		}
 
-		for i2 := i2next; i2 < len(p2); i2++ {
-			lp2 := p2[i2]
-			pr2 := lp2.Ident().ProjectRoot
-
-			switch strings.Compare(string(pr1), string(pr2)) {
-			case 0: // Found a matching project
-				lpd.LockedProjectPropertiesDelta = DiffLockedProjectProperties(lp1, lp2)
-				i2next = i2 + 1 // Don't visit this project again
-			case +1: // Found a new project
-				diff.ProjectDeltas[pr2] = LockedProjectDelta{
-					Name:         pr2,
-					ProjectAdded: true,
+		// Edge case: If there are no lockedProjects on the RHS, they have most probably been removed from the lock file.
+		if len(p2) == 0 {
+			lpd.ProjectRemoved = true
+		} else {
+			for i2 := i2next; i2 < len(p2); i2++ {
+				lp2 := p2[i2]
+				pr2 := lp2.Ident().ProjectRoot
+
+				switch strings.Compare(string(pr1), string(pr2)) {
+				case 0: // Found a matching project
+					lpd.LockedProjectPropertiesDelta = DiffLockedProjectProperties(lp1, lp2)
+					i2next = i2 + 1 // Don't visit this project again
+				case +1: // Found a new project
+					diff.ProjectDeltas[pr2] = LockedProjectDelta{
+						Name:         pr2,
+						ProjectAdded: true,
+					}
+					i2next = i2 + 1 // Don't visit this project again
+					continue        // Keep looking for a matching project
+				case -1: // Project has been removed, handled below
+					lpd.ProjectRemoved = true
 				}
-				i2next = i2 + 1 // Don't visit this project again
-				continue        // Keep looking for a matching project
-			case -1: // Project has been removed, handled below
-				lpd.ProjectRemoved = true
-			}
 
-			break // Done evaluating this project, move onto the next
+				break // Done evaluating this project, move onto the next
+			}
 		}
 
 		diff.ProjectDeltas[pr1] = lpd

gps/verify/lockdiff_test.go

@@ -118,6 +118,10 @@ func TestLockDelta(t *testing.T) {
 			lt:    dup.addII("other.org").rmII("baz.com/qux").addDumbProject("zebrafun.org").rmProject("foo.com/bar"),
 			delta: InputImportsChanged | ProjectRemoved | ProjectAdded,
 		},
+		"remove all projects and imports": {
+			lt:    dup.rmII("baz.com/qux").rmII("foo.com/bar").rmProject("baz.com/qux").rmProject("foo.com/bar").rmProject("transitive.com/dependency"),
+			delta: InputImportsChanged | ProjectRemoved,
+		},
 	}
 
 	for name, fix := range tt {