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> I was just thinking how convenient it is to type emojis right into strings in Python and print them. I assumed C didn't have much unicode compatibility, though I didn't research it.

Libgrapheme is a nice library, but it doesn't really have anything to do with this.

Almost all modern terminal emulators use the UTF-8 character encoding. In order to successfully output Unicode characters, your programming language doesn't actually need much "Unicode support"; it just needs to be able to send UTF-8-encoded bytes to stdout. (That's why many modern programming languages like Go and Zig define strings as a simple array of bytes.) Modern C compilers allow you to printf("é") and get the appropriate behavior.

As you mention, the terminal emulator also needs to be able to decode and display those UTF-8 bytes correctly, and a lot of terminals don't get it right in some situations. Off the top of my head, I don't know of a terminal that actually implements the entire (very complex) set of Unicode text rendering behaviors; maybe one of the web-based ones that run in Electron? macOS's Terminal.app is also pretty good IIRC.

Where libgrapheme comes in is if you want to analyze or manipulate a UTF-8-encoded string. It provides operations like "split into words" and "convert to uppercase". A surprising number of programs never need to do that stuff, but if you do, libgrapheme will give you a Unicode-compatible implementation. (Many more basic operations, like concatenating two strings, will work just fine without libgrapheme.)

(Not a language or Unicode expert, the following likely has important mistakes.)

> Off the top of my head, I don't know of a terminal that actually implements the entire (very complex) set of Unicode text rendering behaviors

There are at least two reasons for this:

First, nobody actually seems to know how bidirectional text should interact with terminal control sequences, or indeed how it should be typeset on a terminal in the first place (what is the primary direction? where are the reordering boundaries?). There is the pre-Unicode bidirectional support mode (BDSM, I kid you not) in ECMA-48[1] and TR/53[2], which AFAIK nobody implements nor cares about; there are terminal emulators endorsed by bidi-language users[3], which AFAIK nobody has written down the behaviour of; there is the Freedesktop bidi terminal spec[4], which is a draft and AFAIK nobody implements yet either but at least some people care about; finally, there are bidi-language users who say that spec is a mistake[5].

Second, aside from bidi and a smattering of other things such as emoji, there is no detailed “Unicode text rendering behaviour”, only standards specific to font formats—the most recent among them being OpenType, which is dubiously compatible across implementations, decently documented only through painstaking reverse engineering (sometimes in words[6], sometimes only in Freetype library code), and generally full of snakes[7]. And it has no notion of a monospace font—only of a (proportional) font where all Lat/Cyr/Grk characters just happen to have the same advance.

AFAICT that is not negligence or an oversight, but rather a concession to the fact that there are scripts which don’t really have a notion of monospace in the typographic tradition and in fact are written such that it’s extremely unclear what monospace would even mean—certainly not one or two cells per codepoint (e.g. Burmese or Tibetan; apparently there are Arabic monospace fonts[8] but I’ve no idea how the hell they work). Not coincidentally, those are the scripts where you really, really need that shaper, otherwise nothing looks anywhere close to correct.

[This post could have been titled “Contra Muratori on Unicode in terminal emulators”.]

[1] https://www.ecma-international.org/publications-and-standard...

[2] https://www.ecma-international.org/publications-and-standard...

[3] https://news.ycombinator.com/item?id=8086417

[4] https://terminal-wg.pages.freedesktop.org/bidi/

[5] http://litcave.rudi.ir/

[6] https://github.com/n8willis/opentype-shaping-documents

[7] https://litherum.blogspot.com/2019/03/addition-font.html

[8] https://news.ycombinator.com/item?id=10395464

Here's another fun Unicode pitfall: does any terminal provide a way to display Chinese and Japanese text simultaneously, using the appropriate versions of the glyphs for each language's characters?

As far as existing terminals are concerned, I don’t know. FWIW, there are similar problems (though only to the point of looking wrong, not of misunderstanding) in other scripts: Cyrillic as used in Bulgarian and a number of other languages[1] and even Latin as used in Polish[2].

Even the Han version, though, does not seem to me to be the sort of “what does it even mean?” problem like those I listed above; more like what you want the input to be. You can make your terminal keep language state, e.g. using the deprecated language tags. Pro: some form of this likely already needs to happen for bidi support; similar to what HTML does. Con: no text file or program ever did this; your nice UTF-8-only terminal is now stateful and goes mad after `head /dev/urandom`. Alternatively, you can require the driving program to emit variation selectors for each Han character. Pro: the state and the ensuing madness is now limited; you can still pretend you’re looking at a stream of characters. Con: no text file or program ever did this; neither does HTML although it theorerically could.

[1] https://commons.wikimedia.org/wiki/File:Cyrillic_alternates....

[2] https://www.twardoch.com/download/polishhowto/kreska.html

> does any terminal provide a way to display Chinese and Japanese text simultaneously, using the appropriate versions of the glyphs

Does any terminal provide a way to display (say) two consecutive lines in different fonts?

Because according to Unicode (and for once I don't particularly disagree), Chinese versus Japanese ideographs are the same characters, drawn in two different fonts.

https://www.facebook.com/appliedphilosophy/photos/a.82854007...

Many years ago I thought the highlighted text was a light hearted joke. Now I see what it is actually quite serious. (And now I understand why, among all people, a Japanese philosopher brought up the issue)

I personally think Unicode didn't go essentialist enough though. There's lots of obscure CJK characters in unicode that, when you look up a dictionary, just says it's another form of a common character. What I heard from people in the know was that the CJK committee basically made an exception for the Japanese because they were threatening to withdraw from the Unicode effort unless their demands were met, and for the most part they got what they wanted.

The "Chinese versus Japanese ideographs are the same characters, drawn in two different fonts" is actually a minority of those cases, which I personally interpret as clerical errors instead of a philosophical disagreement.

For example if Unicode were actually thorough with the essentialist philosophy, 關 and 関 would have the same code point.

No, because it's not actually possible without extra information. The codepoints in Unicode are the same if the languages use the same character (Han unification). With no extra information, if a string is only comprised of unified codepoints, it isn't inherently any one language, so you'd have to resort to a dumb external setting that lets users pick one font in that situation. Next best, you'd have to scan the entire string and find at least one non-unified codepoint and then use that to guess what language it is and then map the correct font for that language. Or, if you have external data such as an encoding string, file metadata, text source, you can simply obey what the metadata says.

Unification was done originally because early versions of Unicode were bit-constrained and there simply was not enough space to have separate codepoints for each language. This would need to be "undone" in some future version of Unicode and text encoders would need to make the backward incompatible change (in terms of rendering in unknown downstream software) of using new codepoints if this were to be done. Then the "proper" font would be deterministic.

> First, nobody actually seems to know how bidirectional text should interact with terminal control sequences...

This goes beyond just bidirectional text. The traditional behavior of text in a terminal is based around two key assumptions, both of which break down catastrophically when dealing with non-ASCII text:

1) The state of a terminal can be represented as a set of cells, each of which has exactly one glyph in it and can be drawn independently from any other cell.

2) Printing a character will write a glyph to the cell the cursor is in and move the cursor to the right by one cell (or down to the next line).

The first assumption breaks down when dealing with full-width characters and ligatures/complex scripts, but can at least be papered over to handle full-width. The second assumption breaks down when exposed to virtually any interesting typographical feature (RTL, combining characters and ZWJ, shaped characters, etc). And I'm not sure it's possible to fix without some pretty substantial changes to how terminals operate -- standard terminal control sequences, and the code that uses them, are all built around these assumptions; introducing new behaviors like "the cursor doesn't always move from left to right" or "erasing the middle of a string might change how the rest of it displays" will break existing applications.

The ECMA standards are of absolutely no help in the matter. They were written in the early 1990s, before Unicode came onto the scene. Their idea of "international language support" was supporting both French and German.

Combining characters don't usually break those rules. They just mean that a single glyph is no longer 1-4 bytes, it's 1-128 or unlimited.

Consider a program that prints "A", waits a second, then prints a combining mark. Before the combining mark shows up, the terminal has no way of knowing to expect one, so it'll render an unaccented "A"; it then has to go back and modify that glyph (breaking the second rule) when the combining mark appears.

A terminal can't defer rendering that "A" until another character shows up -- that'd break common use cases like echoing user input -- and it can't refuse to apply the combining mark just because it arrived later, because the input to a terminal is a stream of bytes, not characters, and that stream can be delayed or interrupted in any number of ways.

And that's without getting into other interactions with terminal features, like: what happens if you move the cursor, or change its attributes, between the base character and its combining mark? How do you apply a combining mark to the last character on a line, since printing that character moves the cursor to the next line? How do combining marks interact with backspace? And so on.

I wouldn't have said that modifying the last-printed glyph breaks rule 2. Either way, I think modifying the glyph is the better answer.

If you send a console command to move the cursor or do anything else to it, the simple answer is to make that a barrier between glyphs. If you output a combining character after doing that, the combining character goes into the next cell all by itself.

Backspace sent to a terminal should move the cursor left by one cell as usual. A backspace sent by a user would probably delete one glyph if no IMEs are involved. If an IME is involved that's a different problem than plain old combining characters.

Being the last character on a line isn't really any different from being in the middle of a line. The cursor auto-moves, but if the next bytes the terminal gets are combining characters then you can pretty easily shove them into the last-printed glyph.

> If you send a console command to move the cursor or do anything else to it, the simple answer is to make that a barrier between glyphs. If you output a combining character after doing that, the combining character goes into the next cell all by itself.

Maybe. I'd be concerned about what effects that might have on applications which need to be able to display multiple streams of output at once, like tmux.

> Being the last character on a line isn't really any different from being in the middle of a line

You might be surprised. After printing the last character on a line, the cursor goes into a weird "wrapnext" state, where the cursor stays at the end of the line, but will wrap to the next line (potentially triggering scrolling) when the next character is output. This state is highly ephemeral; it can't be entered through control sequences, even by DECSC/DECRC.

Oh, cool! Some more links for my "Unicode is a tire fire" collection. (And no, I don't want ASCII back, but finally something sane).

Honestly, to me it looks more like human writing is much more complex than typewriter-tyranny Latin would lead you to believe than that Unicode is a tire fire. (OpenType is a tire fire, though, befitting its history as a final peace treaty between Adobe, Apple, and Microsoft after a decade or two of shifting two-against-one alliances. Good luck convincing the half-dozen or so main font foundries to switch to something else.)

I mean, look at Gujarati[1] and tell me how that thing is ever supposed to fit into character cells. Or think how Hebrew (RTL) text with (LTR) numbers should handle arrow keys in selections[2]—the problem was born in cursed depths where unspeakable ancient monsters breed, you lost (possibly your mind) the moment you decided to solve it. Watch a Japanese user type a romanization of their sentence on a QWERTY keyboard, displayed using the syllabary, and then have the computer guess the word boundaries and offer the appropriate ideograms in a little systemwide overlay[3]—watch and despair. And none of these have anything to do with the way you’ve encoded the strings into bytes. (Unless you tell the Hebrew users to type or process text in reverse, which is also utter insanity.)

[1] https://r12a.github.io/scripts/gujarati/gu.html

[2] https://ltr.wtf/explained/bidiintro.html#selections

[3] https://en.wikipedia.org/wiki/File:IME_demonstratie_-_Matsuo...

I've never seen a Unicode editor that handled Japanese top-to-bottom right-to-left oriented text. Setting up a terminal to switch between Japanese, Farsi, and German on the same screen would be quite a challenge. That's hard even on paper.

The bit encoding is only a very small part of Unicode. That alone would be likely bearable.

It's the whole thing that is problematic.

Unicode mixes way to many concepts in an unholy way. The result is insanity.

The original sin is of course that content and appearance / layout aren't strictly separated.

The whole idea that a text format should be "typewriter compatible" is also a huge part of the problem.

Human script is way too complex that one could pretend that a typewriter abstraction would suffice. But Unicode tries hard to keep this leaky abstraction (because "backwards compatibility"; even it's actually not compatible in all kinds of "corner cases", BIDI being only one). The result is the dumpster fire we've got (and that we likely never ever will get rid of, as it's "good enough" for the majority; I mean as long as you're using European scripts, and no scientific notation, math, and such…).

> And no, I don't want ASCII back, but finally something sane

ASCII was sane (give or take minor annoyances like hexadecimal digits or DEL); the problem was it was too narrowly scoped for general-purpose use. In the context it was actually developed for (exclusively English text on machines that struggled (or didn't bother) to even render 256 different characters, nevermind thousands), ASCII was a broadly-reasonable character encoding that even had half the encoding space left over for something like UTF-8 to build a sensible, more general-purpose encoding in.

Unfortunately, we got specifically UTF-8, with the dumpster fire that is Unicode tied around its neck like a string of albatrosses.

Speaking of "getting" UTF8, I really enjoy this story on it's inception: https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt

> That's why many modern programming languages like Go and Zig define strings as a simple array of bytes.

I'd argue this is not in fact a modern approach but rather a pretty dated one.

Modern language string API design instead leans into 'views' of the underlying depending on what you are trying to do with it.

- Transmission and storage: UTF-8 bytes.

- Parsing: code points.

- Editing: grapheme clusters.

- Rendering: pixels.

It doesn't make sense to consider a random assortment of bytes to be a 'string', that's just an array of random bytes - and the language almost certainly already has a better type for that like a vector of 8-bit unsigned values or a slice type. Strings should be opaque - but always valid - encoded data to be sensible and differentiated from a slice type.

Zig seems to be even worse than Go, requiring null-termination instead of storing them as Pascal strings. This means that a valid substring requires a copy so that the substring can itself be null-terminated to be valid. Inner pointers are not valid unless to the end of the parent and therefore substrings are very expensive relatively speaking.

> Zig seems to be even worse than Go, requiring null-termination instead of storing them as Pascal strings. This means that a valid substring requires a copy so that the substring can itself be null-terminated to be valid. Inner pointers are not valid unless to the end of the parent and therefore substrings are very expensive relatively speaking.

No, Zig uses slices normally (ie ptr + len). Terminators are part of the type system for the (relatively rare, mostly related to C interop) cases where you really want a sentinel value at the end of your array.

I see, I misread the docs. However everything else I stand by, after all it allows you to embed invalid UTF-8 content.

C11 has full support for Unicode in source code for string and char literals and comments. Any runtime Unicode processing, however, has to be provided by outside code.

> If anyone knows of a good one for Linux, please let me know!

kitty has excellent support for this stuff, and is much more performant than anything based on vte (like gnome-terminal).

https://github.com/kovidgoyal/kitty