package merkletrie // The focus of this difftree implementation is to save time by // skipping whole directories if their hash is the same in both // trees. // // The diff algorithm implemented here is based on the doubleiter // type defined in this same package; we will iterate over both // trees at the same time, while comparing the current noders in // each iterator. Depending on how they differ we will output the // corresponding chages and move the iterators further over both // trees. // // The table bellow show all the possible comparison results, along // with what changes should we produce and how to advance the // iterators. // // The table is implemented by the switches in this function, // diffTwoNodes, diffTwoNodesSameName and diffTwoDirs. // // Many Bothans died to bring us this information, make sure you // understand the table before modifying this code. // # Cases // // When comparing noders in both trees you will found yourself in // one of 169 possible cases, but if we ignore moves, we can // simplify a lot the search space into the following table: // // - "-": nothing, no file or directory // - a<>: an empty file named "a". // - a<1>: a file named "a", with "1" as its contents. // - a<2>: a file named "a", with "2" as its contents. // - a(): an empty dir named "a". // - a(...): a dir named "a", with some files and/or dirs inside (possibly // empty). // - a(;;;): a dir named "a", with some other files and/or dirs inside // (possibly empty), which different from the ones in "a(...)". // // \ to - a<> a<1> a<2> a() a(...) a(;;;) // from \ // - 00 01 02 03 04 05 06 // a<> 10 11 12 13 14 15 16 // a<1> 20 21 22 23 24 25 26 // a<2> 30 31 32 33 34 35 36 // a() 40 41 42 43 44 45 46 // a(...) 50 51 52 53 54 55 56 // a(;;;) 60 61 62 63 64 65 66 // // Every (from, to) combination in the table is a special case, but // some of them can be merged into some more general cases, for // instance 11 and 22 can be merged into the general case: both // noders are equal. // // Here is a full list of all the cases that are similar and how to // merge them together into more general cases. Each general case // is labeled wiht an uppercase letter for further reference, and it // is followed by the pseudocode of the checks you have to perfrom // on both noders to see if you are in such a case, the actions to // perform (i.e. what changes to output) and how to advance the // iterators of each tree to continue the comparison process. // // ## A. Impossible: 00 // // ## B. Same thing on both sides: 11, 22, 33, 44, 55, 66 // - check: `SameName() && SameHash()` // - action: do nothing. // - advance: `FromNext(); ToNext()` // // ### C. To was created: 01, 02, 03, 04, 05, 06 // - check: `DifferentName() && ToBeforeFrom()` // - action: inserRecursively(to) // - advance: `ToNext()` // // ### D. From was deleted: 10, 20, 30, 40, 50, 60 // - check: `DifferentName() && FromBeforeTo()` // - action: `DeleteRecursively(from)` // - advance: `FromNext()` // // ### E. Empty file to file with contents: 12, 13 // - check: `SameName() && DifferentHash() && FromIsFile() && // ToIsFile() && FromIsEmpty()` // - action: `modifyFile(from, to)` // - advance: `FromNext()` or `FromStep()` // // ### E'. file with contents to empty file: 21, 31 // - check: `SameName() && DifferentHash() && FromIsFile() && // ToIsFile() && ToIsEmpty()` // - action: `modifyFile(from, to)` // - advance: `FromNext()` or `FromStep()` // // ### F. empty file to empty dir with the same name: 14 // - check: `SameName() && FromIsFile() && FromIsEmpty() && // ToIsDir() && ToIsEmpty()` // - action: `DeleteFile(from); InsertEmptyDir(to)` // - advance: `FromNext(); ToNext()` // // ### F'. empty dir to empty file of the same name: 41 // - check: `SameName() && FromIsDir() && FromIsEmpty && // ToIsFile() && ToIsEmpty()` // - action: `DeleteEmptyDir(from); InsertFile(to)` // - advance: `FromNext(); ToNext()` or step for any of them. // // ### G. empty file to non-empty dir of the same name: 15, 16 // - check: `SameName() && FromIsFile() && ToIsDir() && // FromIsEmpty() && ToIsNotEmpty()` // - action: `DeleteFile(from); InsertDirRecursively(to)` // - advance: `FromNext(); ToNext()` // // ### G'. non-empty dir to empty file of the same name: 51, 61 // - check: `SameName() && FromIsDir() && FromIsNotEmpty() && // ToIsFile() && FromIsEmpty()` // - action: `DeleteDirRecursively(from); InsertFile(to)` // - advance: `FromNext(); ToNext()` // // ### H. modify file contents: 23, 32 // - check: `SameName() && FromIsFile() && ToIsFile() && // FromIsNotEmpty() && ToIsNotEmpty()` // - action: `ModifyFile(from, to)` // - advance: `FromNext(); ToNext()` // // ### I. file with contents to empty dir: 24, 34 // - check: `SameName() && DifferentHash() && FromIsFile() && // FromIsNotEmpty() && ToIsDir() && ToIsEmpty()` // - action: `DeleteFile(from); InsertEmptyDir(to)` // - advance: `FromNext(); ToNext()` // // ### I'. empty dir to file with contents: 42, 43 // - check: `SameName() && DifferentHash() && FromIsDir() && // FromIsEmpty() && ToIsFile() && ToIsEmpty()` // - action: `DeleteDir(from); InsertFile(to)` // - advance: `FromNext(); ToNext()` // // ### J. file with contents to dir with contetns: 25, 26, 35, 36 // - check: `SameName() && DifferentHash() && FromIsFile() && // FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()` // - action: `DeleteFile(from); InsertDirRecursively(to)` // - advance: `FromNext(); ToNext()` // // ### J'. dir with contetns to file with contents: 52, 62, 53, 63 // - check: `SameName() && DifferentHash() && FromIsDir() && // FromIsNotEmpty() && ToIsFile() && ToIsNotEmpty()` // - action: `DeleteDirRecursively(from); InsertFile(to)` // - advance: `FromNext(); ToNext()` // // ### K. empty dir to dir with contents: 45, 46 // - check: `SameName() && DifferentHash() && FromIsDir() && // FromIsEmpty() && ToIsDir() && ToIsNotEmpty()` // - action: `InsertChildrenRecursively(to)` // - advance: `FromNext(); ToNext()` // // ### K'. dir with contents to empty dir: 54, 64 // - check: `SameName() && DifferentHash() && FromIsDir() && // FromIsEmpty() && ToIsDir() && ToIsNotEmpty()` // - action: `DeleteChildrenRecursively(from)` // - advance: `FromNext(); ToNext()` // // ### L. dir with contents to dir with different contents: 56, 65 // - check: `SameName() && DifferentHash() && FromIsDir() && // FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()` // - action: nothing // - advance: `FromStep(); ToStep()` // // // All these cases can be further simplified by a truth table // reduction process, in which we gather similar checks together to // make the final code easier to read and understand. // // The first 6 columns are the outputs of the checks to perform on // both noders. I have labeled them 1 to 6, this is what they mean: // // 1: SameName() // 2: SameHash() // 3: FromIsDir() // 4: ToIsDir() // 5: FromIsEmpty() // 6: ToIsEmpty() // // The from and to columns are a fsnoder example of the elements // that you will find on each tree under the specified comparison // results (columns 1 to 6). // // The type column identifies the case we are into, from the list above. // // The type' column identifies the new set of reduced cases, using // lowercase letters, and they are explained after the table. // // The last column is the set of actions and advances for each case. // // "---" means impossible except in case of hash collision. // // advance meaning: // - NN: from.Next(); to.Next() // - SS: from.Step(); to.Step() // // 1 2 3 4 5 6 | from | to |type|type'|action ; advance // ------------+--------+--------+----+------------------------------------ // 0 0 0 0 0 0 | | | | | if !SameName() { // . | | | | | if FromBeforeTo() { // . | | | D | d | delete(from); from.Next() // . | | | | | } else { // . | | | C | c | insert(to); to.Next() // . | | | | | } // 0 1 1 1 1 1 | | | | | } // 1 0 0 0 0 0 | a<1> | a<2> | H | e | modify(from, to); NN // 1 0 0 0 0 1 | a<1> | a<> | E' | e | modify(from, to); NN // 1 0 0 0 1 0 | a<> | a<1> | E | e | modify(from, to); NN // 1 0 0 0 1 1 | ---- | ---- | | e | // 1 0 0 1 0 0 | a<1> | a(...) | J | f | delete(from); insert(to); NN // 1 0 0 1 0 1 | a<1> | a() | I | f | delete(from); insert(to); NN // 1 0 0 1 1 0 | a<> | a(...) | G | f | delete(from); insert(to); NN // 1 0 0 1 1 1 | a<> | a() | F | f | delete(from); insert(to); NN // 1 0 1 0 0 0 | a(...) | a<1> | J' | f | delete(from); insert(to); NN // 1 0 1 0 0 1 | a(...) | a<> | G' | f | delete(from); insert(to); NN // 1 0 1 0 1 0 | a() | a<1> | I' | f | delete(from); insert(to); NN // 1 0 1 0 1 1 | a() | a<> | F' | f | delete(from); insert(to); NN // 1 0 1 1 0 0 | a(...) | a(;;;) | L | g | nothing; SS // 1 0 1 1 0 1 | a(...) | a() | K' | h | deleteChidren(from); NN // 1 0 1 1 1 0 | a() | a(...) | K | i | insertChildren(to); NN // 1 0 1 1 1 1 | ---- | ---- | | | // 1 1 0 0 0 0 | a<1> | a<1> | B | b | nothing; NN // 1 1 0 0 0 1 | ---- | ---- | | b | // 1 1 0 0 1 0 | ---- | ---- | | b | // 1 1 0 0 1 1 | a<> | a<> | B | b | nothing; NN // 1 1 0 1 0 0 | ---- | ---- | | b | // 1 1 0 1 0 1 | ---- | ---- | | b | // 1 1 0 1 1 0 | ---- | ---- | | b | // 1 1 0 1 1 1 | ---- | ---- | | b | // 1 1 1 0 0 0 | ---- | ---- | | b | // 1 1 1 0 0 1 | ---- | ---- | | b | // 1 1 1 0 1 0 | ---- | ---- | | b | // 1 1 1 0 1 1 | ---- | ---- | | b | // 1 1 1 1 0 0 | a(...) | a(...) | B | b | nothing; NN // 1 1 1 1 0 1 | ---- | ---- | | b | // 1 1 1 1 1 0 | ---- | ---- | | b | // 1 1 1 1 1 1 | a() | a() | B | b | nothing; NN // // c and d: // if !SameName() // d if FromBeforeTo() // c else // b: SameName) && sameHash() // e: SameName() && !sameHash() && BothAreFiles() // f: SameName() && !sameHash() && FileAndDir() // g: SameName() && !sameHash() && BothAreDirs() && NoneIsEmpty // i: SameName() && !sameHash() && BothAreDirs() && FromIsEmpty // h: else of i import ( "fmt" "gopkg.in/src-d/go-git.v4/utils/merkletrie/noder" ) // DiffTree calculates the list of changes between two merkletries. It // uses the provided hashEqual callback to compare noders. func DiffTree(fromTree, toTree noder.Noder, hashEqual noder.Equal) (Changes, error) { ret := NewChanges() ii, err := newDoubleIter(fromTree, toTree, hashEqual) if err != nil { return nil, err } for { from := ii.from.current to := ii.to.current switch r := ii.remaining(); r { case noMoreNoders: return ret, nil case onlyFromRemains: if err = ret.AddRecursiveDelete(from); err != nil { return nil, err } if err = ii.nextFrom(); err != nil { return nil, err } case onlyToRemains: if err = ret.AddRecursiveInsert(to); err != nil { return nil, err } if err = ii.nextTo(); err != nil { return nil, err } case bothHaveNodes: if err = diffNodes(&ret, ii); err != nil { return nil, err } default: panic(fmt.Sprintf("unknown remaining value: %d", r)) } } } func diffNodes(changes *Changes, ii *doubleIter) error { from := ii.from.current to := ii.to.current var err error // compare their full paths as strings switch from.Compare(to) { case -1: if err = changes.AddRecursiveDelete(from); err != nil { return err } if err = ii.nextFrom(); err != nil { return err } case 1: if err = changes.AddRecursiveInsert(to); err != nil { return err } if err = ii.nextTo(); err != nil { return err } default: if err := diffNodesSameName(changes, ii); err != nil { return err } } return nil } func diffNodesSameName(changes *Changes, ii *doubleIter) error { from := ii.from.current to := ii.to.current status, err := ii.compare() if err != nil { return err } switch { case status.sameHash: // do nothing if err = ii.nextBoth(); err != nil { return err } case status.bothAreFiles: changes.Add(NewModify(from, to)) if err = ii.nextBoth(); err != nil { return err } case status.fileAndDir: if err = changes.AddRecursiveDelete(from); err != nil { return err } if err = changes.AddRecursiveInsert(to); err != nil { return err } if err = ii.nextBoth(); err != nil { return err } case status.bothAreDirs: if err = diffDirs(changes, ii); err != nil { return err } default: return fmt.Errorf("bad status from double iterator") } return nil } func diffDirs(changes *Changes, ii *doubleIter) error { from := ii.from.current to := ii.to.current status, err := ii.compare() if err != nil { return err } switch { case status.fromIsEmptyDir: if err = changes.AddRecursiveInsert(to); err != nil { return err } if err = ii.nextBoth(); err != nil { return err } case status.toIsEmptyDir: if err = changes.AddRecursiveDelete(from); err != nil { return err } if err = ii.nextBoth(); err != nil { return err } case !status.fromIsEmptyDir && !status.toIsEmptyDir: // do nothing if err = ii.stepBoth(); err != nil { return err } default: return fmt.Errorf("both dirs are empty but has different hash") } return nil }