ffmt

A fast, configurable Fortran formatter with support for Fypp, Doxygen, and OpenACC/OpenMP directives. Written in Rust. Installable via pip.

Installation

pip install ffmt

Or via Cargo:

cargo install ffmt

Usage

ffmt src/                        # format in-place
ffmt --check src/                # CI mode (exit 1 if changes needed)
ffmt --diff src/                 # show colored diff
ffmt -j 8 src/                   # parallel
cat file.fpp | ffmt -            # stdin/stdout
ffmt --range 10:50 file.fpp      # format only lines 10-50

What it does

• Indentation -- scope-based indentation for all Fortran constructs
• Whitespace -- consistent spacing around operators, commas, colons, parentheses
• Keywords -- case normalization (IF -> if, ENDDO -> end do)
• Continuation lines -- normalized with proportional re-indentation
• Preprocessor -- Fypp (#:if, #:for), OpenACC (!$acc), OpenMP (!$omp) handled correctly

Configuration

Create ffmt.toml or add [tool.ffmt] to pyproject.toml:

indent-width = 4
line-length = 132
keyword-case = "lower"         # lower, upper, preserve
normalize-keywords = true      # enddo -> end do
named-ends = true              # end subroutine -> end subroutine s_foo
align-declarations = true      # align :: in consecutive declarations
unicode-to-ascii = true        # Greek/math symbols -> LaTeX in comments
rewrap-comments = true         # wrap long comments at line-length
rewrap-code = true             # wrap long code lines at line-length
space-after-comment = true     # !comment -> ! comment
collapse-double-spaces = true  # x  =  y -> x = y
keyword-paren-space = true     # if( -> if (
fypp-list-commas = true        # normalize commas in Fypp '[...]' args

[whitespace]
relational = true              # ==, /=, <, <=, >, >=
logical = true                 # .and., .or., .not.
plusminus = true                # binary +, -
multdiv = false                 # *, /
power = false                   # **
assignment = true               # =
declaration = true              # ::
comma = true                    # space after comma

All options have sensible defaults -- most projects need no config file at all.

Preserved as-is

• String literals and inline expressions (${...}$, @{...}@)
• Comment contents and Doxygen alignment (!<, !>, !!)
• Continuation line structure
• #ifdef/#endif blocks (no indentation change)

Editor integration

ffmt includes a built-in LSP server for real-time format-on-save:

ffmt --lsp

VS Code

{
    "fortran.formatting.formatter": "ffmt",
    "fortran.formatting.args": ["--stdin-filepath", "${file}", "-"]
}

Vim/Neovim

autocmd BufWritePost *.fpp,*.f90 silent !ffmt %
" Or: set formatprg=ffmt\ -

Neovim (LSP)

vim.lsp.start({
    name = "ffmt",
    cmd = { "ffmt", "--lsp" },
    root_dir = vim.fs.dirname(vim.fs.find({ "ffmt.toml", "pyproject.toml" }, { upward = true })[1]),
})

CI integration

GitHub Actions

- uses: sbryngelson/ffmt@v0.1.0
  with:
    args: "--check src/"

pre-commit

repos:
  - repo: https://github.com/sbryngelson/ffmt
    rev: v0.1.0
    hooks:
      - id: ffmt

Other Fortran Formatters

License

MIT