Troubleshooting
On the left is what you see on screen, then why it happens and what to type. Every command here was run against this compiler; messages are quoted verbatim (the compiler speaks Russian).
Installing and building
| Symptom | Cause | What to do |
|---|---|---|
There is no flang binary after installing | the compiler is built from four C99 files in bootstrap/, and the machine has no cc or no make. The message «двоичный компилятор не собран» that used to be printed at install time no longer exists in the tree: package.json has neither postinstall nor a scripts field at all (commit 2c40752d0) | sudo apt install build-essential (Fedora — sudo dnf install gcc make, Alpine — apk add build-base, macOS — xcode-select --install), then make -C bootstrap |
make: command not found when building from a clone | make is only there to compile four C files | build with a single cc call — the command is below |
asdf install flang refuses: the archive holds a different file name | the asdf plugin lives in a separate repository and lags behind the tree | brew install digitable-lol/tap/flang, or build from source |
The built flang is not found | make -C bootstrap puts it in bootstrap/flang, not on PATH | sudo make -C bootstrap install, or call ./bootstrap/flang |
Building without make is one call to the C compiler:
cd bootstrap
cc -std=c99 -Wall -Wextra -Werror -pedantic -O2 -o flang \
flang_cli.c flang_repl.c flang_runtime.c compiler_flang.c -lm -lpthreadThe check does not answer, or answers about the wrong thing
| Symptom | Cause | What to do |
|---|---|---|
flang check on a big file thinks for a while and ends with FLANG_RECURSION_LIMIT | the step budget is one for the whole command, and check has no key that raises the limit | check one file at a time and split the module into smaller ones |
flang check names a line and column that do not exist in your file | the trouble lives in an imported module, and the diagnostic carries no file name | check every imported module with its own command |
"замечаний 1" and not a word about postconditions: --proof prints nothing | the check stopped at the first trouble — it never reached the postconditions, and the claims were not judged at all | fix the trouble; while it stands, "proved" means nothing |
FLANG_IMPORT_NOT_FOUND: не найден модуль «Имя»: ни рядом с файлом, ни выше по каталогам, ни в библиотеке компилятора | the lookup by module name alone found no file | give the path outright: использует «Имя» из "path/file.flang" |
flang emit exited with code 3 and the files are written | the program declares something the binary does not judge — a monad, for instance (a program with processes, or with morphisms and no category, is emitted with code 0 today; run of 11 September 2026, binary 0.7.17, commit 2c40752d0, on the examples of the «Language reference» page) | this is not a refusal to emit: judge such a program by its examples (flang test) |
Trouble in an imported module looks like this — line 7 belongs to the neighbouring file, not to the one you checked:
FLANG_UNKNOWN_NAME, строка 7, столбец 17: имя «неизвестное» не связаноThe cure is to check one file at a time:
flang check neighbour.flangA plan run hits a limit
| Symptom | Cause | What to do |
|---|---|---|
FLANG_RECURSION_LIMIT: функция «Имя» исчерпала лимит шагов (10000000) на глубине вызовов N, exit code 1 | flang io allows 10,000,000 steps per turn by default | raise it: flang io plan.flang --max-steps 100000000 |
FLANG_RECURSION_LIMIT: функция «Имя» превысила предел глубины вызовов (10000) | the call depth limit is 10,000 | --max-depth N, or better, rewrite the recursion as a fold |
| The plan stops early and names no trouble | the default budget is 10,000 orders per run | --max-orders N |
To see that the message is exactly this one, force it with a tiny limit:
flang run docs/examples/rosetta/factorial.flang --function 'Факториал' --args '{"н":30}' --max-steps 3It prints FLANG_RECURSION_LIMIT: функция «Факториал» исчерпала лимит шагов (3) на глубине вызовов 1 and exits with code 1.
Processes after emitting into another language
The scheduler is not emitted into every target. A program with processes behaves differently depending on where you emitted it:
| Target | What happens |
|---|---|
c, elixir, js, ts | the scheduler is emitted (for c it is flang_conc.c next to the program), exit code 0 |
cpp, csharp, go, java, python, rust | emitting refuses outright, exit code 1, not a single file written |
Taken on docs/examples/service-on-processes/service.flang (three processes, a supervisor, three runs).
The refusal for go reads verbatim:
flang emit: печать отказала — у цели «go» нет планировщика конкурентности, а в программе
объявлена конкурентность (процессов 3, надзоров 1, прогонов 3), первый — процесс «Приёмная».
Напечатать процессы в «go» нечем: обработчик стал бы обычной функцией, которую никто
не зовёт, и программа собралась бы, делая не то, что написано. Цели с планировщиком: c, elixir, jsWhat to do: emit a program with processes into c, elixir, js or ts (the refusal names three targets; ts is missing from it although it does emit — same run).
flang emit your-file.flang --target elixir --out ./outputThe language server in the editor
| Symptom | Cause | What to do |
|---|---|---|
| The editor is configured and there are no hints or squiggles | the editor cannot start flang lsp: the binary is not on PATH | check the server command in the editor settings — Setting up your editor; flang check % on a key works without the server |
| No highlighting in Emacs | highlighting exists for Vim, Neovim and VS Code only | use flang check % on a key — see the same page |
One command tells you whether the server is alive:
printf 'Content-Length: 75\r\n\r\n{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"capabilities":{}}}' | flang lsp --stdioNext: Setting up your editor and Installing.