Text output: terminal and Markdown

Renderers over a line-token TextDiff. Output is a pure function of the diff and the renderer's settings: the same input gives the same bytes on every platform. Every output line ends in \n, whatever the input's line endings.

Hunks (both formats)

• Lines are the line tokens of the diff. A line's terminator (\n, \r\n or a lone \r) is not shown.
• A change is surrounded by ContextLines equal lines (default 3). Two changes whose gap is at most twice that share one hunk, so no line appears twice. With 0 context every change is its own hunk.
• A hunk starts with @@ -a,b +c,d @@: one-based first line and line count on each side. A count of 1 is written without ,1. An empty range names the line before it (-0,0 at the start of the text).
• Lines are prefixed ' ' (context), - (only in the old text) and + (only in the new text). Deletions of a changed block come before its insertions.
• A shown line that had no terminator is followed by \ No newline at end of file.
• When OldName or NewName is set, --- old and +++ new precede the first hunk.
• An identical pair renders as the empty string.

Terminal

• Colour (default on): hunk headers cyan (ESC[36m), file headers bold, deletions red (ESC[31m), insertions green (ESC[32m), the no-newline note dim; each styled line ends with ESC[0m. Colour off writes the same text without any escape sequence.
• Word level (colour on only): in a changed block that has both deleted and inserted lines, the block's old and new lines are diffed word by word and the changed words are wrapped in reverse video (ESC[7m … ESC[27m). Skipped when either side of the block exceeds 8192 chars, or when under 30% of the longer side (counting non-white-space chars) is shared — those lines are rewrites and marking everything is noise.
• Control characters in the text (below U+0020 except tab, U+007F, U+0080–U+009F) are replaced by a visible picture (U+2400 block, U+2421, U+FFFD) so compared text cannot drive the terminal.

Markdown

• Line diff: the hunks above in a fenced block opened with diff. The fence is three backticks, or one more than the longest backtick run in the content.
• Inline diff (any token kind): the new text, each deletion wrapped in <del> and each insertion in <ins>. A run that spans line breaks is wrapped per line, with the breaks outside the tags. & and < are escaped as & and <; other Markdown is left as written. <del>/<ins> is used rather than ~~/** because those collide with markup already in the text and cannot be escaped reliably.

Reading views

Three views read a TextDiff without token arithmetic.

• TextDiff.Pieces: one DiffRun(Kind, OldLine, NewLine, Text) per edit run, with the run's text as it stands (line breaks included) and the 1-based line each side starts on (null on the side that lacks the run). Works for every token kind.
• TextDiff.Lines: the pieces cut at line breaks (\n, \r\n, a lone \r), the breaks dropped. For a line diff that is one entry per line; for a word or character diff a changed line shows as several entries with the same line number. A side's line number advances when a piece starts a new line on that side, so an unterminated last line is one line.
• Diff.SideBySide(old, new) / SideBySideDiff.From(lineDiff): aligned rows. A run of deleted lines followed by a run of inserted lines is paired line by line into Modified rows (the longer run's remainder is Deleted or Inserted rows with the other cell null). A modified row's cells hold word-level Parts from Diff.Words plus semantic cleanup of the two lines: Equal and Delete on the left, Equal and Insert on the right. Needs a diff made with line tokens.