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Chandler CarruthandRichard Smith
9c486de2de
Rich diagnostic rendering needs a layer underneath it that knows what the attached terminal can do and can position styled text in two dimensions. This adds that layer, both as the foundation the diagnostics rendering work will build on and as something usable directly for ordinary CLI output. Nothing depends on it yet, so it lands and is reviewed on its own. Four libraries, each with its own tests: - `color`: a color, either one of the 16 named ANSI colors or a 24-bit RGB value, and the escape sequences that select it at a given color depth. - `style`: colors plus text attributes, and the escapes that move a terminal from one style to another. - `capabilities`: what the terminal behind a stream supports, detected from the environment. - `buffer`: a grid of styled cells that layout code draws into and that renders itself once. Rationale for the design decisions lives in the headers, next to what it explains. Four things are worth review attention in particular: - The color detection precedence documented on `ChooseColorMode`. It settles how a `--color` flag, `NO_COLOR`, `CLICOLOR`, `FORCE_COLOR`, and the terminal itself interact. The policy is a pure function of those inputs, so the whole table is tested without touching the process environment. - `Charset`, which decides whether any UTF-8 processing happens at all. Column counts only follow from code points if the terminal agrees about the encoding, so anything short of a locale naming UTF-8 is treated as bytes. - `Buffer` owning column accounting instead of its callers, which is what keeps double-width characters, combining marks, and stray bytes from misaligning everything after them. - The API surface, which is held to operations that nothing else covers. Junctions in line art come only from lines overlapping, and turning a style on or off is spelled as a transition to or from the default style. `terminal_benchmark` covers style transitions, full-screen rendering, and text drawing. On an M-series laptop, rendering an 80x24 screen in which every cell changes style costs about 14us with color off and 76-95us with it, and drawing a 40-column line of source costs about 140ns without UTF-8 processing and 394ns with it. Assisted-by: Gemini and Claude --------- Co-authored-by: Richard Smith <richard@metafoo.co.uk>