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‎README.md

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# Top 10 Recommendations for Fortran Modernization
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Modernizing Fortran codebases is a crucial step toward improving code quality
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and ensuring maintainability. It helps developers uncover hidden bugs and
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reduces the risk of introducing new errors during development. Additionally,
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these efforts support modern compilers and tools in generating optimized code
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and identifying potential issues early. Ultimately, modernization boosts
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developer productivity and enhances code robustness.
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## Context and motivation
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This project is inspired by the [OWASP](https://owasp.org/) community-led
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initiative, which regularly publishes the most relevant Top 10 Secure Coding
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Recommendations. These are widely adopted by the industry to help developers
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avoid common security vulnerabilities. The OWASP initiative thrives on
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collaboration and knowledge sharing through platforms like their [GitHub
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repository](https://github.com/OWASP/Top10).
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Beyond OWASP, various open catalogs provide comprehensive collections of checks
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(rules) to help ensure secure coding practices. Each check describes specific
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scenarios and necessary actions, offering extensive documentation, example
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codes, automated code analysis tools, and references to other resources.
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Notable examples include [SEI CERT
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C](https://wiki.sei.cmu.edu/confluence/display/c) and
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[CWE](https://cwe.mitre.org/).
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Building on these foundations, this project aims to start a similar
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community-driven initiative focused on modern Fortran software development.
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Leveraging the existing [Open Catalog on Best Practices for Modernization and
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Performance](https://github.com/codee-com/open-catalog/), we seek to establish
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a dedicated set of Top 10 Recommendations and related checks to address the
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specific challenges of Fortran Modernization.
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Modernizing Fortran code encompasses updating and maintaining legacy Fortran
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codes (e.g., F77, F90) with extensive development histories. It also involves
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refactoring existing Fortran codes to leverage the features of the latest
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Fortran standards (e.g., transitioning from F90 to F23).
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## Methodology
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To develop the Top 10 Recommendations for Fortran Modernization, we adopted a
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comprehensive and community-focused approach. First, we conducted an extensive
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review of existing resources on the topic to identify an initial draft of the
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most recurrent recommendations. These were later discussed with the Fortran
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development community to collect insights and feedback (e.g., in Fortran
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Discourse
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[[12](https://fortran-lang.discourse.group/t/our-initiative-to-publish-the-fortran-lang-top-10-recommendation-for-fortran-modernization-is-it-really-new-or-even-feasible/7774)]),
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which were crucial for shaping the final proposal.
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The presented Top 10 Recommendations are prioritized to guide developers
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through a progression of modernization efforts. Each recommendation is detailed
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with specific checks that describe actionable steps, including examples of
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before and after code snippets, the rationale behind the changes, and links to
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further reading.
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To ensure the recommendations remain relevant and comprehensive, we plan to
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continuously review community input and update the guidelines as the Fortran
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standards evolve and new best practices emerge.
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## Top 10 Recommendations
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1. [Strict compliance with modern Fortran
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standards](Recommendations/R1_ModernStandardCompliance.md).
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2. [Declare procedures in modules](Recommendations/R2_ProceduresInModules.md).
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3. [Restrict data visibility with
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modules](Recommendations/R3_RestrictDataVisibility.md).
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4. [Improve dummy arguments
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semantics](Recommendations/R4_ImproveDummyArguments.md).
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5. [Improve data type consistency and
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management](Recommendations/R5_ImproveDataTypes.md).
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6. [Avoid legacy control-flow
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constructs](Recommendations/R6_AvoidLegacyControlFlow.md).
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7. [Enhance source code semantics](Recommendations/R7_EnhanceCodeSemantics.md).
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8. [Adhere to code conventions](Recommendations/R8_CodeConventions.md).
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9. [Adopt modern development
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practices](Recommendations/R9_ModernDevelopmentPractices.md).
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10. [Proper C/C++ interoperability](Recommendations/R10_CInteroperability.md).
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## References
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- [1] Fortran Community. "Fortran Best Practices". Accessed: Jun. 06, 2024.
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[Online] Available: https://fortran-lang.org/en/learn/best_practices/
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- [2] Fortran Wiki Contributors. "Modernizing Old Fortran". Accessed: Jun. 06,
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2024. [Online] Available:
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https://fortranwiki.org/fortran/show/Modernizing+Old+Fortran
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- [3] Fortran Discourse Community. "Fortran Discourse". Accessed: Jun. 06,
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2024. [Online] Available: https://fortran-lang.discourse.group
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- [4] Reinhold Bader. "Fortran code modernization". Accessed: Jun. 06, 2024.
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[Online] Available:
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https://www.ugent.be/hpc/en/training/2018/modern_fortran_materials/modernfortran2018.pdf
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- [5] The Numerical Algorithms Group. "Fortran Modernisation Workshop".
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Accessed: Jun. 06, 2024. [Online] Available:
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https://blog.rwth-aachen.de/hpc_import_20210107/attachments/39157901/39420371.pdf
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- [6] The Carpentries. "Best Practices in Modern Fortran". Accessed: Jun. 06,
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2024. [Online] Available:
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https://wvuhpc.github.io/Modern-Fortran/11-Best-Practices/index.html
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- [7] Norman S. Clerman, Walter Spector. "Modern Fortran: Style and Usage". 1st
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Edition, 2011.
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- [8] Michael Metcalf, John Reid, Malcolm Cohen, Reinhold Bader. "Modern
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Fortran Explained". 6th Edition, 2023.
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- [9] Fortran Users of NERSC (FUN). "FUN Training July 2023: Modern Fortran
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Basics". Accessed: Jun. 06, 2024. [Online] Available:
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https://www.nersc.gov/users/training/past-training-events/2023/fun-training-july-2023-modern-fortran-basics/
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- [10] Jack Carlson, Olaf David. "Fortran 90/95 Coding Conventions - Fortran
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Features that are obsolescent and/or discouraged". Accessed: Jun. 06, 2024.
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[Online] Available:
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https://alm.engr.colostate.edu/cb/wiki/16983#section-Fortran+Features+that+are+obsolescent+and_2For+discouraged
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- [11] GitHub Collaborators. "Best practices and styles guidelines of Fortran
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FOSS Programmers". Accessed: Jun. 06, 2024. [Online] Available:
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https://github.com/Fortran-FOSS-Programmers/Best_Practices
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- [12] Fortran Discourse Community. "Our initiative to publish the
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'Fortran-lang Top 10 Recommendation for Fortran modernization', is it really
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new or even feasible?". Accessed: Jun. 06, 2024. [Online] Available:
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https://fortran-lang.discourse.group/t/our-initiative-to-publish-the-fortran-lang-top-10-recommendation-for-fortran-modernization-is-it-really-new-or-even-feasible/7774
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- [13] GitHub Collaborators. "Open Catalog of Best Practices for Modernization
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and Optimization". Accessed: Jun. 06, 2024. [Online] Available:
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https://github.com/codee-com/open-catalog

‎Recommendations/R10_CInteroperability.md

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# 10. Proper C/C++ interoperability
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## Overview
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Ensure seamless interoperability between Fortran and C/C++ to allow Fortran
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programs to effectively interact with a wide range of systems and libraries
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written in other languages (e.g., high-performance environments).
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## Checks
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- _Planned: Encapsulate calls to external programming models in specific
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procedures or modules._

‎Recommendations/R1_ModernStandardCompliance.md

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# 1. Strict compliance with modern Fortran standards
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## Overview
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Remove legacy features deleted from recent Fortran standards, as they might not
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be supported by recent compilers, and avoid compiler-specific extensions,
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ensuring that the code remains compatible across various development
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environments.
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## Checks
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- _Planned: Tune compiler flags to mark features removed from recent Fortran
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standards._
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- _Planned: Tune compiler flags to mark compiler-specific constructs._

‎Recommendations/R2_ProceduresInModules.md

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# 2. Declare procedures in modules
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## Overview
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Declare related procedures within an importable module to enhance code
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modularity, reusability, and readability. This practice also helps avoid
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runtime errors related to implicit interfaces. Separate the definition of
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procedures into modules and their implementation into submodules, leveraging
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incremental compilation to reduce build times.
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## Checks
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- [PWR068](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR068):
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Encapsulate external procedures within modules to avoid the risks of calling
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implicit interfaces.
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- _Planned: Consider moving the module's procedure implementations into a
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separate submodule._

‎Recommendations/R3_RestrictDataVisibility.md

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# 3. Restrict data visibility with modules
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## Overview
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Encapsulate globally accessible data, such as common blocks, within modules.
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This approach allows for controlled access interfaces, improving code
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readability and minimizing side effects from global data storage.
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## Checks
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- [PWR073](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR073):
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Transform common block into a module for better data encapsulation.
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- [PWR069](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR069):
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Use the keyword only to explicitly state what to import from a module.
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- _Planned: Minimize mutable module variables by passing data as procedure
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arguments._
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- _Planned: Privatize mutable module variables and add procedures for more
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controlled access._

‎Recommendations/R4_ImproveDummyArguments.md

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# 4. Improve dummy arguments semantics
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## Overview
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Enhance the definitions of dummy arguments to make the behavior of procedures
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more predictable and transparent, helping avoid common issues related to
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incorrect assumptions about data type, flow, or structure.
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## Checks
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- [PWR008](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR008):
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Declare the intent for each procedure argument.
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- [PWR070](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR070):
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Declare array dummy arguments as assumed-shape arrays.
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- _Planned: Add a contiguous attribute to applicable assumed-shape arrays._

‎Recommendations/R5_ImproveDataTypes.md

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# 5. Improve data type consistency and management
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## Overview
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Ensure the consistency of data types by avoiding implicit typing and
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standardizing the code on a fixed set of real kinds, improving readability and
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portability across different development environments. Use derived data types
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to represent complex multi-field structures. Leverage pointers and allocatable
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arrays for safer memory handling.
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## Checks
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- [PWR007](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR007):
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Always use implicit none to disable implicit declarations.
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- [PWR071](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR071):
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Prefer real(kind=kind_value) for declaring consistent floating types.
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- _Planned: Prefer derived types over constructs such as structure or record to
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represent complex multi-field entities_.
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- _Planned: Replace equivalence statements by pointers or the transfer
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intrinsic as needed._
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- _Planned: Consider replacing fixed-size arrays with allocatables._

‎Recommendations/R6_AvoidLegacyControlFlow.md

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# 6. Avoid legacy control-flow constructs
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## Overview
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Replace outdated and error-prone control-flow constructs with more robust and
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maintainable language features from recent standards, improving code
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maintainability and reducing the likelihood of bugs.
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## Checks
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- [PWR063](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR063):
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Avoid using legacy Fortran constructs.
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- _Planned: Use case or if-then-else constructs instead of go to statements for
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conditional flow._
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- _Planned: Use do, cycle, and exit constructs instead of go to statements for
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loops._
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- _Planned: Replace arithmetic if statements with block if constructs._
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- _Planned: Convert numbered do loops to modern do loops._
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- _Planned: End all loops with an end do statement._
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- _Planned: Use only integer control variables in do loops._
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- _Planned: Replace forall statements with do-concurrent constructs._
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- _Planned: Avoid alternate return statements._
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- _Planned: Replace compiler-dependant short-circuit logic with nested
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conditionals._

‎Recommendations/R7_EnhanceCodeSemantics.md

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# 7. Enhance source code semantics
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## Overview
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Leverage elements from recent Fortran standards to further improve the clarity
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and intent of code statements beyond previous recommendations.
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## Checks
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- [PWR003](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR003):
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Explicitly declare pure functions.
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- [PWR072](https://github.com/codee-com/open-catalog/blob/main/Checks/PWR072):
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Add an explicit save attribute when initializing variables in their
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declaration.
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- _Planned: Prefer variable initializations at declaration instead of data or
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block data statements._
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- _Planned: Add an explicit parameter attribute to constant variables._
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- _Planned: Explicitly declare elemental functions._

‎Recommendations/R8_CodeConventions.md

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# 8. Adhere to code conventions
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## Overview
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Establish and adhere to a consistent coding standard, such as variable naming
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rules of free-form format, to promote readability and ease collaboration among
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developers.
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## Checks
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- _Planned: Tune compiler flags to mark fixed-form Fortran code._

‎Recommendations/R9_ModernDevelopmentPractices.md

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# 9. Adopt modern development practices
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## Overview
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Integrate modern development practices, such as automated testing, version
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control, or dependency managers, to enhance the quality, maintainability,
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collaboration, and distribution of Fortran software.
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## Checks
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_Work in progress_

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