mirror of https://github.com/go-gitea/gitea.git
429 lines
14 KiB
Go
429 lines
14 KiB
Go
package merkletrie
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// The focus of this difftree implementation is to save time by
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// skipping whole directories if their hash is the same in both
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// trees.
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//
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// The diff algorithm implemented here is based on the doubleiter
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// type defined in this same package; we will iterate over both
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// trees at the same time, while comparing the current noders in
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// each iterator. Depending on how they differ we will output the
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// corresponding changes and move the iterators further over both
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// trees.
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//
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// The table bellow show all the possible comparison results, along
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// with what changes should we produce and how to advance the
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// iterators.
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//
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// The table is implemented by the switches in this function,
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// diffTwoNodes, diffTwoNodesSameName and diffTwoDirs.
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//
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// Many Bothans died to bring us this information, make sure you
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// understand the table before modifying this code.
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// # Cases
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//
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// When comparing noders in both trees you will find yourself in
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// one of 169 possible cases, but if we ignore moves, we can
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// simplify a lot the search space into the following table:
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//
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// - "-": nothing, no file or directory
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// - a<>: an empty file named "a".
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// - a<1>: a file named "a", with "1" as its contents.
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// - a<2>: a file named "a", with "2" as its contents.
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// - a(): an empty dir named "a".
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// - a(...): a dir named "a", with some files and/or dirs inside (possibly
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// empty).
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// - a(;;;): a dir named "a", with some other files and/or dirs inside
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// (possibly empty), which different from the ones in "a(...)".
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//
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// \ to - a<> a<1> a<2> a() a(...) a(;;;)
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// from \
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// - 00 01 02 03 04 05 06
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// a<> 10 11 12 13 14 15 16
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// a<1> 20 21 22 23 24 25 26
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// a<2> 30 31 32 33 34 35 36
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// a() 40 41 42 43 44 45 46
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// a(...) 50 51 52 53 54 55 56
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// a(;;;) 60 61 62 63 64 65 66
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//
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// Every (from, to) combination in the table is a special case, but
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// some of them can be merged into some more general cases, for
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// instance 11 and 22 can be merged into the general case: both
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// noders are equal.
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//
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// Here is a full list of all the cases that are similar and how to
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// merge them together into more general cases. Each general case
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// is labeled with an uppercase letter for further reference, and it
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// is followed by the pseudocode of the checks you have to perfrom
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// on both noders to see if you are in such a case, the actions to
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// perform (i.e. what changes to output) and how to advance the
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// iterators of each tree to continue the comparison process.
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//
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// ## A. Impossible: 00
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//
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// ## B. Same thing on both sides: 11, 22, 33, 44, 55, 66
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// - check: `SameName() && SameHash()`
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// - action: do nothing.
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// - advance: `FromNext(); ToNext()`
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//
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// ### C. To was created: 01, 02, 03, 04, 05, 06
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// - check: `DifferentName() && ToBeforeFrom()`
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// - action: insertRecursively(to)
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// - advance: `ToNext()`
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//
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// ### D. From was deleted: 10, 20, 30, 40, 50, 60
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// - check: `DifferentName() && FromBeforeTo()`
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// - action: `DeleteRecursively(from)`
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// - advance: `FromNext()`
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//
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// ### E. Empty file to file with contents: 12, 13
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// - check: `SameName() && DifferentHash() && FromIsFile() &&
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// ToIsFile() && FromIsEmpty()`
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// - action: `modifyFile(from, to)`
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// - advance: `FromNext()` or `FromStep()`
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//
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// ### E'. file with contents to empty file: 21, 31
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// - check: `SameName() && DifferentHash() && FromIsFile() &&
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// ToIsFile() && ToIsEmpty()`
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// - action: `modifyFile(from, to)`
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// - advance: `FromNext()` or `FromStep()`
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//
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// ### F. empty file to empty dir with the same name: 14
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// - check: `SameName() && FromIsFile() && FromIsEmpty() &&
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// ToIsDir() && ToIsEmpty()`
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// - action: `DeleteFile(from); InsertEmptyDir(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### F'. empty dir to empty file of the same name: 41
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// - check: `SameName() && FromIsDir() && FromIsEmpty &&
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// ToIsFile() && ToIsEmpty()`
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// - action: `DeleteEmptyDir(from); InsertFile(to)`
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// - advance: `FromNext(); ToNext()` or step for any of them.
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//
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// ### G. empty file to non-empty dir of the same name: 15, 16
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// - check: `SameName() && FromIsFile() && ToIsDir() &&
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// FromIsEmpty() && ToIsNotEmpty()`
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// - action: `DeleteFile(from); InsertDirRecursively(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### G'. non-empty dir to empty file of the same name: 51, 61
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// - check: `SameName() && FromIsDir() && FromIsNotEmpty() &&
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// ToIsFile() && FromIsEmpty()`
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// - action: `DeleteDirRecursively(from); InsertFile(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### H. modify file contents: 23, 32
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// - check: `SameName() && FromIsFile() && ToIsFile() &&
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// FromIsNotEmpty() && ToIsNotEmpty()`
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// - action: `ModifyFile(from, to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### I. file with contents to empty dir: 24, 34
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// - check: `SameName() && DifferentHash() && FromIsFile() &&
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// FromIsNotEmpty() && ToIsDir() && ToIsEmpty()`
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// - action: `DeleteFile(from); InsertEmptyDir(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### I'. empty dir to file with contents: 42, 43
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// - check: `SameName() && DifferentHash() && FromIsDir() &&
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// FromIsEmpty() && ToIsFile() && ToIsEmpty()`
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// - action: `DeleteDir(from); InsertFile(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### J. file with contents to dir with contents: 25, 26, 35, 36
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// - check: `SameName() && DifferentHash() && FromIsFile() &&
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// FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()`
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// - action: `DeleteFile(from); InsertDirRecursively(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### J'. dir with contents to file with contents: 52, 62, 53, 63
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// - check: `SameName() && DifferentHash() && FromIsDir() &&
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// FromIsNotEmpty() && ToIsFile() && ToIsNotEmpty()`
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// - action: `DeleteDirRecursively(from); InsertFile(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### K. empty dir to dir with contents: 45, 46
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// - check: `SameName() && DifferentHash() && FromIsDir() &&
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// FromIsEmpty() && ToIsDir() && ToIsNotEmpty()`
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// - action: `InsertChildrenRecursively(to)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### K'. dir with contents to empty dir: 54, 64
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// - check: `SameName() && DifferentHash() && FromIsDir() &&
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// FromIsEmpty() && ToIsDir() && ToIsNotEmpty()`
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// - action: `DeleteChildrenRecursively(from)`
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// - advance: `FromNext(); ToNext()`
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//
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// ### L. dir with contents to dir with different contents: 56, 65
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// - check: `SameName() && DifferentHash() && FromIsDir() &&
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// FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()`
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// - action: nothing
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// - advance: `FromStep(); ToStep()`
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//
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//
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// All these cases can be further simplified by a truth table
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// reduction process, in which we gather similar checks together to
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// make the final code easier to read and understand.
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//
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// The first 6 columns are the outputs of the checks to perform on
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// both noders. I have labeled them 1 to 6, this is what they mean:
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//
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// 1: SameName()
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// 2: SameHash()
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// 3: FromIsDir()
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// 4: ToIsDir()
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// 5: FromIsEmpty()
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// 6: ToIsEmpty()
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//
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// The from and to columns are a fsnoder example of the elements
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// that you will find on each tree under the specified comparison
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// results (columns 1 to 6).
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//
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// The type column identifies the case we are into, from the list above.
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//
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// The type' column identifies the new set of reduced cases, using
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// lowercase letters, and they are explained after the table.
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//
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// The last column is the set of actions and advances for each case.
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//
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// "---" means impossible except in case of hash collision.
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//
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// advance meaning:
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// - NN: from.Next(); to.Next()
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// - SS: from.Step(); to.Step()
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//
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// 1 2 3 4 5 6 | from | to |type|type'|action ; advance
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// ------------+--------+--------+----+------------------------------------
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// 0 0 0 0 0 0 | | | | | if !SameName() {
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// . | | | | | if FromBeforeTo() {
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// . | | | D | d | delete(from); from.Next()
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// . | | | | | } else {
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// . | | | C | c | insert(to); to.Next()
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// . | | | | | }
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// 0 1 1 1 1 1 | | | | | }
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// 1 0 0 0 0 0 | a<1> | a<2> | H | e | modify(from, to); NN
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// 1 0 0 0 0 1 | a<1> | a<> | E' | e | modify(from, to); NN
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// 1 0 0 0 1 0 | a<> | a<1> | E | e | modify(from, to); NN
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// 1 0 0 0 1 1 | ---- | ---- | | e |
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// 1 0 0 1 0 0 | a<1> | a(...) | J | f | delete(from); insert(to); NN
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// 1 0 0 1 0 1 | a<1> | a() | I | f | delete(from); insert(to); NN
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// 1 0 0 1 1 0 | a<> | a(...) | G | f | delete(from); insert(to); NN
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// 1 0 0 1 1 1 | a<> | a() | F | f | delete(from); insert(to); NN
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// 1 0 1 0 0 0 | a(...) | a<1> | J' | f | delete(from); insert(to); NN
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// 1 0 1 0 0 1 | a(...) | a<> | G' | f | delete(from); insert(to); NN
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// 1 0 1 0 1 0 | a() | a<1> | I' | f | delete(from); insert(to); NN
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// 1 0 1 0 1 1 | a() | a<> | F' | f | delete(from); insert(to); NN
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// 1 0 1 1 0 0 | a(...) | a(;;;) | L | g | nothing; SS
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// 1 0 1 1 0 1 | a(...) | a() | K' | h | deleteChildren(from); NN
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// 1 0 1 1 1 0 | a() | a(...) | K | i | insertChildren(to); NN
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// 1 0 1 1 1 1 | ---- | ---- | | |
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// 1 1 0 0 0 0 | a<1> | a<1> | B | b | nothing; NN
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// 1 1 0 0 0 1 | ---- | ---- | | b |
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// 1 1 0 0 1 0 | ---- | ---- | | b |
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// 1 1 0 0 1 1 | a<> | a<> | B | b | nothing; NN
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// 1 1 0 1 0 0 | ---- | ---- | | b |
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// 1 1 0 1 0 1 | ---- | ---- | | b |
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// 1 1 0 1 1 0 | ---- | ---- | | b |
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// 1 1 0 1 1 1 | ---- | ---- | | b |
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// 1 1 1 0 0 0 | ---- | ---- | | b |
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// 1 1 1 0 0 1 | ---- | ---- | | b |
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// 1 1 1 0 1 0 | ---- | ---- | | b |
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// 1 1 1 0 1 1 | ---- | ---- | | b |
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// 1 1 1 1 0 0 | a(...) | a(...) | B | b | nothing; NN
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// 1 1 1 1 0 1 | ---- | ---- | | b |
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// 1 1 1 1 1 0 | ---- | ---- | | b |
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// 1 1 1 1 1 1 | a() | a() | B | b | nothing; NN
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//
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// c and d:
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// if !SameName()
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// d if FromBeforeTo()
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// c else
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// b: SameName) && sameHash()
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// e: SameName() && !sameHash() && BothAreFiles()
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// f: SameName() && !sameHash() && FileAndDir()
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// g: SameName() && !sameHash() && BothAreDirs() && NoneIsEmpty
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// i: SameName() && !sameHash() && BothAreDirs() && FromIsEmpty
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// h: else of i
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import (
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"context"
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"errors"
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"fmt"
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"github.com/go-git/go-git/v5/utils/merkletrie/noder"
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)
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var (
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// ErrCanceled is returned whenever the operation is canceled.
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ErrCanceled = errors.New("operation canceled")
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)
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// DiffTree calculates the list of changes between two merkletries. It
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// uses the provided hashEqual callback to compare noders.
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func DiffTree(
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fromTree,
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toTree noder.Noder,
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hashEqual noder.Equal,
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) (Changes, error) {
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return DiffTreeContext(context.Background(), fromTree, toTree, hashEqual)
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}
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// DiffTreeContext calculates the list of changes between two merkletries. It
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// uses the provided hashEqual callback to compare noders.
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// Error will be returned if context expires
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// Provided context must be non nil
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func DiffTreeContext(ctx context.Context, fromTree, toTree noder.Noder,
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hashEqual noder.Equal) (Changes, error) {
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ret := NewChanges()
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ii, err := newDoubleIter(fromTree, toTree, hashEqual)
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if err != nil {
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return nil, err
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}
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for {
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select {
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case <-ctx.Done():
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return nil, ErrCanceled
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default:
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}
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from := ii.from.current
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to := ii.to.current
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switch r := ii.remaining(); r {
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case noMoreNoders:
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return ret, nil
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case onlyFromRemains:
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if err = ret.AddRecursiveDelete(from); err != nil {
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return nil, err
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}
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if err = ii.nextFrom(); err != nil {
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return nil, err
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}
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case onlyToRemains:
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if err = ret.AddRecursiveInsert(to); err != nil {
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return nil, err
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}
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if err = ii.nextTo(); err != nil {
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return nil, err
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}
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case bothHaveNodes:
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if err = diffNodes(&ret, ii); err != nil {
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return nil, err
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}
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default:
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panic(fmt.Sprintf("unknown remaining value: %d", r))
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}
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}
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}
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func diffNodes(changes *Changes, ii *doubleIter) error {
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from := ii.from.current
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to := ii.to.current
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var err error
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// compare their full paths as strings
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switch from.Compare(to) {
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case -1:
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if err = changes.AddRecursiveDelete(from); err != nil {
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return err
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}
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if err = ii.nextFrom(); err != nil {
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return err
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}
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case 1:
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if err = changes.AddRecursiveInsert(to); err != nil {
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return err
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}
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if err = ii.nextTo(); err != nil {
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return err
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}
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default:
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if err := diffNodesSameName(changes, ii); err != nil {
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return err
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}
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}
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return nil
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}
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func diffNodesSameName(changes *Changes, ii *doubleIter) error {
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from := ii.from.current
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to := ii.to.current
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status, err := ii.compare()
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if err != nil {
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return err
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}
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switch {
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case status.sameHash:
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// do nothing
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if err = ii.nextBoth(); err != nil {
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return err
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}
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case status.bothAreFiles:
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changes.Add(NewModify(from, to))
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if err = ii.nextBoth(); err != nil {
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return err
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}
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case status.fileAndDir:
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if err = changes.AddRecursiveDelete(from); err != nil {
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return err
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}
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if err = changes.AddRecursiveInsert(to); err != nil {
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return err
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}
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if err = ii.nextBoth(); err != nil {
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return err
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}
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case status.bothAreDirs:
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if err = diffDirs(changes, ii); err != nil {
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return err
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}
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default:
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return fmt.Errorf("bad status from double iterator")
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}
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return nil
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}
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func diffDirs(changes *Changes, ii *doubleIter) error {
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from := ii.from.current
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to := ii.to.current
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status, err := ii.compare()
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if err != nil {
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return err
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}
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switch {
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case status.fromIsEmptyDir:
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if err = changes.AddRecursiveInsert(to); err != nil {
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return err
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}
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if err = ii.nextBoth(); err != nil {
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return err
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}
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case status.toIsEmptyDir:
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if err = changes.AddRecursiveDelete(from); err != nil {
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return err
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}
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if err = ii.nextBoth(); err != nil {
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return err
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}
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case !status.fromIsEmptyDir && !status.toIsEmptyDir:
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// do nothing
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if err = ii.stepBoth(); err != nil {
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return err
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}
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default:
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return fmt.Errorf("both dirs are empty but has different hash")
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}
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return nil
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}
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