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FORTRAN Language Server for the Language Server Protocol

Project description

A Fortran implementation of the Language Server Protocol using Python (2.7+ or 3.0+).

Editor extensions using this language server to provide autocomplete and other IDE-like functionality are available for Atom, Visual Studio Code, Visual Studio, (Neo)vim, and Emacs.

Note: This language server is currently in the early stages of development. Not all features are supported or planned.

Language Server Features

Document Symbols:

Auto Completion:

Signature Help:

Note: Not available for overloaded subroutines/functions.

Go to definition:


Find references:

Note: Currently for global and top level module objects only.


  • Multiple use of the same variable name
  • Unknown module in USE statement
  • Variable masking definition from parent scope


pip install fortran-language-server

Language server settings

The following global settings can be used when launching the language server.

  • --symbol_skip_mem Do not include type members in document symbol results
  • --incremental_sync Use incremental document synchronization (beta)
  • --autocomplete_no_prefix Do not filter autocomplete results by variable prefix
  • --lowercase_intrinsics Use lowercase for intrinsics and keywords in autocomplete requests
  • --use_signature_help Use signature help instead of snippets for subroutines/functions
  • --variable_hover Show hover information for variables (default: subroutines/functions only)
  • --debug_log Write debug information to root_dir/fortls_debug.log (requires a specified root_dir during initialization)

Debug settings:

The following settings can be used to perform standalone debug tests on the language server.

  • --debug_filepath=DEBUG_FILEPATH File path for language server tests
  • --debug_rootpath=DEBUG_ROOTPATH Root path for language server tests
  • --debug_line=DEBUG_FILEPATH Line position for language server tests (1-indexed)
  • --debug_char=DEBUG_ROOTPATH Character position for language server tests (1-indexed)
  • --debug_parser Test source code parser on specified file
  • --debug_symbols Test symbol request for specified file
  • --debug_workspace_symbols=QUERY_STRING Test workspace/symbol request for project-wide search
  • --debug_completion Test completion request for specified file and position
  • --debug_signature Test signatureHelp request for specified file and position
  • --debug_definition Test definition request for specified file and position


Project specific settings can be specified by placing a JSON file named .fortls (example below) in the root_dir directory.

  • lowercase_intrinsics Use lowercase for intrinsics and keywords in autocomplete requests (default: false)
  • debug_log Write debug information to root_dir/fortls_debug.log (default: false)

Setup module search paths:

By default all files with the suffix F,F77,F90,F95,F03,F08,FOR,FPP (case-insensitive) in the root_dir directory, specified during initialization, and all its sub-directories are parsed and included in the project.

Directories and files can be excluded from the project by specifying their paths (relative to root_dir) in the excl_paths variable in the .fortls file. Excluded directories also exclude all sub-directories. Source files with a common suffix may also be excluded using the excl_suffixes variable.

Module directories can also be specified manually by specifying their paths (relative to root_dir) in the mod_dirs variable in the .fortls file. When mod_dirs is specified directories are not added recursively, so any nested sub directories must be explicitly listed. However, root_dir does not need to be specified manually as it is always included.

  "mod_dirs": ["subdir1", "subdir2"],
  "excl_paths": ["subdir3", "subdir1/file_to_skip.F90"],
  "excl_suffixes": ["_skip.f90"],
  "lowercase_intrinsics": false,
  "debug_log": false

Bug reports

When filing bugs please provide example code to reproduce the observed issue.


This project is made available under the MIT License.


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Project details

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