fortfmt-fix

A small, deterministic codemod that rewrites Intel/DEC omitted-width Fortran FORMAT descriptors (e.g., I, F.d, E.dE#, G.d, L) to standard-conforming forms (e.g., I12, F25.16), improving portability across compilers (gfortran, ifx, etc.).

Quickstart

Installation

# From PyPI (when available)
pip install fortfmt-fix

# From source (development mode)
git clone https://github.com/anl-cec/fortfmt-fix.git
cd fortfmt-fix
pip install -e .

Command Line Usage

# Show proposed changes without modifying files
fortfmt-fix --dry-run path/to/src

# Apply changes in-place
fortfmt-fix --in-place path/to/src

# Process specific files
fortfmt-fix --dry-run file1.f90 file2.f90

# Process directories recursively
fortfmt-fix --in-place src/

Python API

from fortran_format_codemod import transform_source

# Basic usage
result = transform_source("WRITE(*,'(I)') i")
# Returns: "WRITE(*,'(I12)') i"

# With flags
result = transform_source(
    "WRITE(*,'(I)') i", 
    int64=True,           # Use I23 instead of I12
    listify_reads=True,   # Convert safe READ statements to list-directed
    trace=True            # Enable debug output
)

Default Widths

The tool applies the following default widths when omitted:

Examples

Basic FORMAT Statement

! Before
FORMAT(I, F.6, E.12E3)

! After
FORMAT(I12, F25.6, E25.12E3)

Nested Groups with Repeat Counts

! Before
WRITE(*,'(1X, 2(F.6, 1X), I)') a, b, c

! After  
WRITE(*,'(1X, 2(F25.6, 1X), I12)') a, b, c

READ Statement Listification

! Before (with --listify-reads)
read(5, '(I, I, F.6)') i, j, x

! After
read(5, *) i, j, x

Command Line Options

• --dry-run - Show proposed changes without modifying files
• --in-place - Apply changes directly to files
• --int64 - Use wider integer defaults (I23 instead of I12) for 64-bit I/O
• --listify-reads - Convert safe READ statements to list-directed form
• --trace - Enable verbose debug output

Safety & Idempotence

fortfmt-fix is designed to be safe and idempotent:

• Conservative: Only transforms omitted-width descriptors, never touches explicit widths
• Idempotent: Running the tool multiple times produces identical results
• Preserves semantics: Quoted strings and non-format content are never modified
• Deterministic: No random behavior or network calls

Recommended Usage

For best results, use as a pre-commit hook to catch format issues early:

# Install pre-commit
pip install pre-commit

# Add to .pre-commit-config.yaml
repos:
  - repo: local
    hooks:
      - id: fortfmt-fix
        name: fortfmt-fix
        entry: fortfmt-fix --dry-run
        language: system
        files: \.(f90|F90|f|F)$

Testing

The package includes comprehensive tests covering:

• Basic descriptor transformations
• Nested groups and continuation lines
• Flag behavior (--int64, --listify-reads)
• Idempotence verification
• Edge cases and malformed input handling
• CLI smoke tests

Run tests with:

pytest -q

See Also

• docs/OSS-Approval-OnePager.md - Project overview and approval
• JOSS/paper.md - Academic paper describing the tool
• CHANGELOG.md - Version history and changes