# CheckFortranSourceCompiles

Check if given Fortran source compiles and links into an executable.

`check_fortran_source_compiles`

      check_fortran_source_compiles(<code> <resultVar>
          [FAIL_REGEX <regex>...]
          [SRC_EXT <extension>]
      )

  Checks that the source supplied in `<code>` can be compiled as a Fortran source file and linked as an executable. The `<code>` must be a Fortran program containing at least an `end` statement–for example:

      check_fortran_source_compiles("character :: b; error stop b; end" F2018ESTOPOK SRC_EXT F90)

  This command can help avoid costly build processes when a compiler lacks support for a necessary feature, or a particular vendor library is not compatible with the Fortran compiler version being used. This generate-time check may advise the user of such before the main build process. See also the `check_fortran_source_runs()` command to actually run the compiled code.

  The result will be stored in the internal cache variable `<resultVar>`, with a boolean true value for success and boolean false for failure.

  If `FAIL_REGEX` is provided, then failure is determined by checking if anything in the output matches any of the specified regular expressions.

  By default, the test source file will be given a `.F` file extension. The `SRC_EXT` option can be used to override this with `.<extension>` instead– `.F90` is a typical choice.

  The underlying check is performed by the `try_compile()` command. The compile and link commands can be influenced by setting any of the following variables prior to calling `check_fortran_source_compiles()`:

  `CMAKE_REQUIRED_FLAGS`
    Additional flags to pass to the compiler. Note that the contents of `CMAKE_Fortran_FLAGS` and its associated configuration-specific variable are automatically added to the compiler command before the contents of `CMAKE_REQUIRED_FLAGS`.
  `CMAKE_REQUIRED_DEFINITIONS`
    A ;-list of compiler definitions of the form `-DFOO` or `-DFOO=bar`. A definition for the name specified by `<resultVar>` will also be added automatically.
  `CMAKE_REQUIRED_INCLUDES`
    A ;-list of header search paths to pass to the compiler. These will be the only header search paths used by `try_compile()`, i.e. the contents of the `INCLUDE_DIRECTORIES` directory property will be ignored.
  `CMAKE_REQUIRED_LINK_OPTIONS`
    A ;-list of options to add to the link command (see `try_compile()` for further details).
  `CMAKE_REQUIRED_LIBRARIES`
    A ;-list of libraries to add to the link command. These can be the name of system libraries or they can be Imported Targets (see `try_compile()` for further details).
  `CMAKE_REQUIRED_QUIET`
    If this variable evaluates to a boolean true value, all status messages associated with the check will be suppressed.

  The check is only performed once, with the result cached in the variable named by `<resultVar>`. Every subsequent CMake run will re-use this cached value rather than performing the check again, even if the `<code>` changes. In order to force the check to be re-evaluated, the variable named by `<resultVar>` must be manually removed from the cache.