d7ad3d09f7
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015f73FesGZGYPkmDvUcj6QX
92 lines
4.7 KiB
Markdown
92 lines
4.7 KiB
Markdown
# Finch, for SchOS's own programs
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**Two things, and only one of them is later.**
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- *Bringing Finch into SchOS* (below) is **later** — behind [1.0.md](1.0.md)'s
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freeze like everything else here that is not named there.
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- *Finishing Finch itself*, and making it fully self-hosting, is work on the
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Finch repository and does not touch this tree. It can proceed now; see
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[the gap](#the-self-hosting-gap).
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Finch is the author's own language: <https://pandor.pl/git/nexoniarz/Finch>
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(GitHub mirror: `Nexoniarz/Finch`). The plan is to write SchOS's own
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applications and tools in it, in place of C, and so leave behind what C does
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badly: silent narrowing, signed/unsigned mixing, undefined behaviour on an
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out-of-range index, a forgotten `free`.
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## What it is today (version 2.4.0)
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Measured from the repository, not from its README alone:
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- **LLVM front end**, C-like syntax, no semicolons, no headers, no preprocessor.
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It compiles through LLVM's `-O2` pipeline to native code; there is no
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garbage collector.
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- **Values, not references:** lists, text and structs copy on assignment and
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are freed at the end of their block. Out-of-range indexes, division by zero
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and null pointers stop with a runtime error rather than undefined behaviour.
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- **Errors as values** (`int(s) or 0`, `try read_file(p)`), maps, methods,
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modules.
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- **C interop through libclang:** `import "foo.h"` plus `link "foo"` calls any C
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library, structs by value and callbacks included. That is the way in to
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everything SchOS already has — musl, the `/dev/*` interfaces, Alpine's
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libraries.
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- **Targets:** Linux, macOS, Windows, on x86-64 and ARM64 (`src/target.cpp`;
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the System V, AAPCS64 and Microsoft x64 ABIs are in `src/abi.cpp`).
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- **Tooling:** a language server (`finch lsp`), VS Code and Kate support, 74
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tests.
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- **Self-hosting:** `boot/` is a Finch compiler written in Finch (about 3,100
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lines, against about 5,900 for the C++ one in `src/`, language server included) that builds itself to a
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byte-identical result — `tests/boot.sh`.
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## What SchOS would need to do
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1. **A `schos` target.** `finch` picks a triple, a C compiler and a linker per
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target. SchOS runs unmodified Alpine binaries and Alpine's musl
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(see [alpine.md](alpine.md)), so the first target is **the existing
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`x86_64-unknown-linux-musl`**, and a Finch program built on the host should
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run on SchOS before anything in Finch is made SchOS-specific. Test that
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before writing a line of target code.
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2. **The compiler on SchOS.** Needs LLVM 21 and libclang, both of which Alpine
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packages. That is a question of apk and memory, not of SchOS.
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3. **`boot/` as the SchOS-hosted compiler.** The C++ compiler needs LLVM's C++
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libraries; the one in `boot/` is the candidate for being the compiler that
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ships in the image, once it emits through LLVM's C API or a smaller
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back end.
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4. **Bindings** for SchOS's own interfaces (`/dev/pci`, `/dev/netdev`,
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schinit's job protocol, the framebuffer) — generated by the C importer from
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the headers in `include/uapi/`, so they are not hand-written and cannot
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drift from the kernel.
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## Where self-hosting stands
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The Finch compiler written in Finch (`boot/`) now **builds itself**: stage 2 and
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stage 3 are byte-identical (58,660 lines of LLVM IR), and it passes all 22 of
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the repository's run tests (the C++ one passes 77/77). The work is on the
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`finish-finch` branch of `github.com/Nexoniarz/Finch`; `before-bootstrap` there
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is the all-C++ compiler, kept as the backup. `main` is untouched.
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What the self-hosted compiler has: sized numbers, methods, `defer`, errors as
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values, maps, `for k, v in`, C import through libclang (written in Finch, in
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`boot/cimport.fch`), C structs by value and `addr(fn)` callbacks (System V
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x86-64), `run`, `build`, `ir`, `version`, `-O0`, `-l`, `-I`.
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What it does **not** have yet, and the C++ compiler does:
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| `-g` debug info | text IR needs the DWARF metadata written by hand |
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| `--target` (Windows, ARM64, macOS) | their struct-passing rules (`abi.cpp`) and linkers |
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| `lsp`, the editor language server | `lsp.cpp`, 580 lines |
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| `export fn`, `build --shared` | on the author's local `embed` branch |
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**`main` becomes the Finch-written compiler when those are in**, so that
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nothing a user does today stops working; until then it is the seed that builds
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the first stage. The new language features (enums, `match`, generics, a
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standard library) come before that switch, as simple as the rest of the language.
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## Rules
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- Inference, not an instruction: the kernel stays in C. Finch is for
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applications and tools; the user said "our apps or stuff like that".
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- No new capability starts until [the register of unfinished work](1.0.md#the-freeze-and-the-register-of-unfinished-work)
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is empty; the SchOS half of this document is a plan, not an exception to that.
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