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Fix line diff by using rune index without a separator #136
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Fix line diff by using runes without separators
[The suggested approach](https://github.com/google/diff-match-patch/wiki/Line-or-Word-Diffs#line-mode ) for doing line level diffing is the following set of steps: 1. `ti1, ti2, linesIdx = DiffLinesToChars(t1, t2)` 2. `diffs = DiffMain(ti1, ti2)` 3. `DiffCharsToLines(diff, linesIdx)` The original implementation in `google/diff-match-patch` uses unicode codepoints for storing indices in `ti1` and `ti2` joined by an empty string. Current implementation in this repo stores them as integers joined by a comma. While this implementation makes `ti1` and `ti2` more readable, it introduces bugs when trying to rely on it when doing line level diffing with `DiffMain`. The root cause of the issue is that an integer line index might span more than one character/rune, and `DiffMain` can assume that two different lines having the same index prefix match partially. For example, indices 123 and 129 will have partial match `12`. In that example, the diff will show lines 3 and 9 which is not correct. A simple failing test case demonstrating this issue is available at `TestDiffPartialLineIndex`. In this PR I am adjusting the algorithm to use the same approach as in [diff-match-patch](https://github.com/google/diff-match-patch/blob/62f2e689f498f9c92dbc588c58750addec9b1654/javascript/diff_match_patch_uncompressed.js#L508-L510 ) by storing each line index as a rune. While a rune in Golang is a type alias to uint32, not every uint32 can be a valid rune. During string to rune slice conversion invalid runes will be replaced with `utf.RuneError`. The integer to rune generation logic is based on the table in https://en.wikipedia.org/wiki/UTF-8#Encoding The first 127 lines will work the fastest as they are represented as a single bytes. Higher numbers are represented as 2-4 bytes. In addition to that, the range `U+D800 - U+DFFF` contains [invalid codepoints](https://en.wikipedia.org/wiki/UTF-8#Invalid_sequences_and_error_handling). and all codepoints higher or equal to `0xD800` are incremented by `0xDFFF - 0xD800`. The maximum representable integer using this approach is 1'112'060. This improves on Javascript implementation which currently [bails out](https://github.com/google/diff-match-patch/blob/62f2e689f498f9c92dbc588c58750addec9b1654/javascript/diff_match_patch_uncompressed.js#L503-L505 ) when files have more than 65535 lines.
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Original file line number | Diff line number | Diff line change |
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@@ -8,4 +8,4 @@ require ( | |
gopkg.in/yaml.v2 v2.4.0 // indirect | ||
) | ||
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go 1.12 | ||
go 1.13 | ||
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Upgrading to go 1.13 in order to use binary and hex integer literals.