ffmt 0.2.3

A fast, configurable Fortran formatter with Fypp, Doxygen, and OpenACC/OpenMP support

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

General

Option	Default	Description
indent-width	4	Number of spaces per indentation level.
line-length	132	Maximum line length. Code and comments are wrapped at this limit. Set to 1000 to disable wrapping.
keyword-case	"lower"	Case for Fortran keywords: "lower", "upper", or "preserve".
normalize-keywords	true	Split compound keywords like enddo into end do.
named-ends	true	Add procedure/module name to bare end statements (end subroutine -> end subroutine s_foo).
align-declarations	true	Vertically align :: in consecutive declaration blocks.
unicode-to-ascii	true	Replace Unicode Greek letters and math symbols with LaTeX equivalents in comments (σ -> \sigma).
rewrap-comments	true	Re-wrap long comments at line-length, splitting at word boundaries. Doxygen !> / !! blocks are joined and re-wrapped as units.
rewrap-code	true	Re-wrap long code lines at line-length using token-aware splitting (never breaks inside numbers or strings).
space-after-comment	true	Ensure a space after ! in regular comments (!comment -> ! comment). Does not affect !$acc, !<, !>, !!, or !&.
collapse-double-spaces	true	Collapse runs of multiple spaces to a single space in code (not in strings or comments).
keyword-paren-space	true	Add a space between control-flow keywords and ( (if( -> if (). Applies to if, call, allocate, select case, where, etc.
fypp-list-commas	true	Normalize comma spacing inside Fypp '[...]' list arguments.
indent-fypp	true	Indent Fypp preprocessor blocks (#:if, #:for, #:call).
indent-module	true	Indent the body of module and program blocks.

Whitespace

The [whitespace] section controls spacing around specific operators:

Option	Default	Description
relational	true	Space around ==, /=, <, <=, >, >=.
logical	true	Space around .and., .or., .not., .eqv., .neqv..
plusminus	true	Space around binary + and -.
multdiv	false	Space around * and /.
power	false	Space around **.
assignment	true	Space around = in assignments.
pointer	true	Space around =>.
concatenation	true	Space around // (string concatenation).
declaration	true	Space around :: in declarations.
comma	true	Space after ,.
slice-colon	false	Space around : in array slices.

Files

Option	Default	Description
extensions	["fpp", "f90", "F90", "f95", "f03", "F", "F95", "F03"]	File extensions to format.
exclude	[]	Glob patterns to exclude.
respect-gitignore	true	Skip files listed in .gitignore.

Example

indent-width = 4
line-length = 132
keyword-case = "lower"
normalize-keywords = true

[whitespace]
relational = true
logical = true
plusminus = true
multdiv = false
power = false
assignment = true
declaration = true
comma = true

Preserved as-is

• String literals and inline expressions (${...}$, @{...}@)
• Comment contents and Doxygen alignment (!<, !>, !!)
• Continuation line structure across #ifdef/#:if preprocessor blocks
• #ifdef/#endif blocks (no indentation change)
• Fypp/Python code inside $: and @: macro invocations

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@latest
  with:
    args: "--check src/"

pre-commit

repos:
  - repo: https://github.com/sbryngelson/ffmt
    rev: v0.2.1
    hooks:
      - id: ffmt

To auto-update to the latest version, run:

pre-commit autoupdate

Or use pre-commit.ci to update hooks automatically via pull requests.

Other Fortran Formatters

Formatter	Language	Status	Notes
fprettify	Python	Unmaintained (last release 2020)	Free-form only. Fypp support. Requires multiple passes for convergence.
findent	C	Active	Indentation and fixed/free conversion. No whitespace normalization.
Codee Formatter	Proprietary	Active	Commercial. Tree-sitter based. Fixed and free-form.
LFortran fmt	Rust	In development	AST-based. Part of the LFortran compiler project.
Fortitude	Rust	Active	Linter with auto-fix, not a full formatter. Tree-sitter based.
f90-mode	Emacs Lisp	Active	Emacs built-in. Indentation only.

License

MIT