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Fortran code analysis tool

Project description

Flint is a framework for building Fortran code analysis tools in Python. It includes a basic command line tool for linting and code checks, and also provides a framework for developing custom tests.

More generally, flint provides an interface to a Fortran source code project within a Python environment.

Flint is in the early stages of development, but currently provides some basic functionality.


In most cases, flint can be installed with

python install --user

If you want to install it in your system directories (and have permission):

python install

This may not work for some users, and more elegant installation methods ought to be available in the future, depending on how well-received this project becomes.

Basic usage

Current functionality is described below. During this very early stage of development, features may change, expand, or be dropped without any notice.


Use flint to invoke the CLI. The following tools have been implemented with limited features.

flint report

Apply a generic linter and static analysis to a Fortran project.

The following tests are included:

  • Trailing whitespace

  • Indents with mixed tabs and spaces

  • Tabs within statements

  • Excessive line length (both with and without comments)

flint gendoc

Generates a reST documentation file based on docstrings in the source code. Currently follows the Doxygen convention.

flint format

In principle, this will provide a formatted version of an input source code. Currently, it returns each statement with whitespace and comments removed.

flint tag

Return the input files, with statements tagged based on type. For example, a module statement is tagged with the letter M.

This is primarily a debugging tool, but might be of interest to users.

Development API

Flint provides an interface to the details of the source code, which can be used to develop tools which are customized to your project.

To parse the source code, create a Project and call parse() over the top-level directory of the project.

from flint.project import Project

proj = Project()

The proj in this example will contain several containers describing the contents of the source code. (NOTE: This is limited to the current needs of the developers, but is expected to grow over time.)

For example, the following code block will return a list of all the modules and its derived types.

for mod in proj.modules:
    for dtype in mod.derived_types:

(More concrete examples to follow)

For more examples, inspect the flint/tools directory, which describe the command line tools.

How it Works

Flint is broken into three stages, which closely resemble compiler frontends.

  1. The Scanner object takes an input stream and returns the “lexemes”, the “words” of the grammar. No semantic meaning is attached to them at this stage.

    One important feature of Scanner is that it also preserves the nonsemantic lexemes. Examples include grouped whitespace, endlines, and comments.

    Users would generally not use the Scanner since it is a component of the Lexer, which is described below.

  2. The lexemes are passed to the Lexer, which is structured as an iterator. It has three major responsibilities:

    1. Lexemes are identified as either semantic or liminal, which is our term for non-semantic tokens such as whitespace, comments, or statement separators (;).

    2. Lexemes are converted from lines to Statements. A statement may span many lines (&), or a line may contain many statements (;). The Lexer will resolve these cases and return the next semantic Statement.

    3. Preprocessing is applied at this stage. Macro substitutions are applied, but the original macro name is preserved.

    Each iteration of the lexer returns a Statement, which is a list subclass containing the Token lexemes.

    Each Token contains a head and tail, which point to lists of the “liminals” inbewteen the semantic lexemes. This includes whitespace (including endlines), line breaks (&), statement terminators (;), and comments. Each Token preserves its original case, but uses lowercase for general operations, such as comparison tests or dictionary keys.

    There is also a PToken subclass from preprocessed content. These tokens display as the original unprocessed lexemes, but are evaluated as the postprocessed value. For example, macros appear unchanged but use their substituted value in comparison tests. Values from an #include statement appear as empty strings but are returned as semantically valid statements.

    Although we call these “tokens”, they are not quite equivalent to the tokens produced by a compiler’s parser, since we do not yet classify them into, for example, identifiers or operators. There is some advantage in deferring this, since most Fortran keywords can also be used as identifiers.

    As with the Scanner, most users will never need to interact with the Lexer, which is a component of the Parser described below.

  3. Finally, the Lexer output is passed to the Parser, which interprets the semantic contents to recreate an abstraction of the source code and its components.

    This is where modules, subprograms, variables, and other content are organized into equivalent data structures which can be probed and traversed for further analysis.

    The Parser is contained with the Source objects, which represent abstractions of the source code (aka “translation units” in compiler-talk).

    If working as intended, this should be the only level at which the user is required to interact with the parser.

    This is currently the least developed part of flint, so at this point I will just say to watch this space for future work.

Unimplemented Features

The “unknown unknowns” probably exceed the “known unknowns” at this stage, but we are aware of the following issues.

  • The Fortran expressions themselves remain unparsed beyond identification of its tokens. Further parsing such as AST generation is not yet attempted.

  • Expressions inside of an #if or #elif statement are not parsed, and for simplicity are currently assumed to always be false.

    To fix this would require a full expression parser, which is not yet available.

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