Git Diffcore Transformations: Merging and String Detection

document, even if you added 910 new lines to make a new 1000-line document, you did not do a complete rewrite. diffcore-break breaks such a case in order to help diffcore-rename to consider such filepairs as a candidate of rename/copy detection, but if filepairs broken that way were not matched with other filepairs to create rename/copy, then this transformation merges them back into the original "modification". The "extent of changes" parameter can be tweaked from the default 80% (that is, unless more than 80% of the original material is deleted, the broken pairs are merged back into a single modification) by giving a second number to -B option, like these: * -B50/60 (give 50% "break score" to diffcore-break, use 60% for diffcore-merge-broken). * -B/60 (the same as above, since diffcore-break defaults to 50%). Note that earlier implementation left a broken pair as separate creation and deletion patches. This was an unnecessary hack, and the latest implementation always merges all the broken pairs back into modifications, but the resulting patch output is formatted differently for easier review in case of such a complete rewrite by showing the entire contents of the old version prefixed with '-', followed by the entire contents of the new version prefixed with '+'. diffcore-pickaxe: For Detecting Addition/Deletion of Specified String --------------------------------------------------------------------- This transformation limits the set of filepairs to those that change specified strings between the preimage and the postimage in a certain way. -S<block-of-text> and -G<regular-expression> options are used to specify different ways these strings are sought. "-S<block-of-text>" detects filepairs whose preimage and postimage have different number of occurrences of the specified block of text. By definition, it will not detect in-file moves. Also, when a changeset moves a file wholesale without affecting the interesting string, diffcore-rename kicks in as usual, and `-S` omits the filepair (since the number of occurrences of that string didn't change in that rename-detected filepair). When used with `--pickaxe-regex`, treat the <block-of-text> as an extended POSIX regular expression to match, instead of a literal string. "-G<regular-expression>" (mnemonic: grep) detects filepairs whose textual diff has an added or a deleted line that matches the given regular expression. This means that it will detect in-file (or what rename-detection considers the same file) moves, which is noise. The implementation

Git's diffcore transformations include merging broken filepairs and detecting changes to specified strings, with options like -B, -S, and -G allowing for customization of the merging and detection processes, including the use of regular expressions and literal strings to identify changes.