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https://github.com/polysquare/cmake-header-language

CMake macro to determine the language of a header file
https://github.com/polysquare/cmake-header-language

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CMake macro to determine the language of a header file

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# CMake Determine Header Language #



CMake macro to determine the language of a header file.



## Status ##



| Travis CI (Ubuntu) | AppVeyor (Windows) | Coverage | Biicode | Licence |

|--------------------|--------------------|----------|---------|---------|

|[![Travis](https://img.shields.io/travis/polysquare/cmake-header-language.svg)](http://travis-ci.org/polysquare/cmake-header-language)|[![AppVeyor](https://img.shields.io/appveyor/ci/smspillaz/cmake-determine-header-language.svg)](https://ci.appveyor.com/project/smspillaz/cmake-determine-header-language)|[![Coveralls](https://img.shields.io/coveralls/polysquare/cmake-header-language.svg)](http://coveralls.io/polysquare/cmake-header-language)|[![Biicode](https://webapi.biicode.com/v1/badges/smspillaz/smspillaz/cmake-header-language/master)](https://www.biicode.com/smspillaz/cmake-header-language)|[![License](https://img.shields.io/github/license/polysquare/cmake-header-language.svg)](http://github.com/polysquare/cmake-header-language)|



## Description ##



`cmake-determine-header-language` can be used to detect the language of header

files based on what other files include them.  This can be used for various bits

of build tooling, where the build tooling itself quite require a language to be

explicitly set for the header file to be scanned.



## Usage ##



`cmake-determine-header-language` works by scanning source files for `#include`

statements and then checks the passed include directories for files matching the

name of files specified in the `#include` statements.



### Scanning for header files ###



You can scan a source file for headers recursively using

`psq_scan_source_for_headers`.  The macro will apply the following rules

to any detected header file.



* If source file including the header is a C++ source and the header file was

  not already marked as a C source, then the language of the header is set to

  CXX

* If the source file including the header is a C source, then the header will

  unconditionally be marked as a C header.

* If, when scanning the header, certain indicators such as `__cplusplus` or

  any of the indicators specified in `CPP_IDENTIFIERS` were found, then the

  header is set to C and C++



See, for example:



    psq_scan_source_for_headers (SOURCE /my_source.c

                                 INCLUDES /path/to/include/dir

                                 CPP_IDENTIFIERS

                                 MY_SOURCE_IS_COMPILING_CXX)



### Getting the language of any source ###



Once sources have been scanned for header files, their language can be obtained

with `psq_determine_language_for_source`.  If this function is used on a

header which was not part of an already scanned source, then a fatal error will

result.



See, for example:



    psq_determine_language_for_source (/my_header.h LANGUAGE WAS_HEADER)



`LANGUAGE` will be set to C, CXX or both should the header be able to be

compiled in both modes.  `WAS_HEADER` will be set to TRUE if the scanned source

was a header, FALSE otherwise.



## Reference ##



### `psq_source_type_from_source_file_extension` ###



Returns the initial type of a source file from its extension. It doesn't

properly analyze headers and source inclusions to determine the language

of any headers.



The type of the source will be set in the variable specified in

RETURN_TYPE. Valid values are C_SOURCE, CXX_SOURCE, HEADER and UNKNOWN



* `SOURCE`: Source file to scan

* `RETURN_TYPE`: Variable to set the source type in



### `psq_scan_source_for_headers` ###



Opens the source file `SOURCE` at its absolute path and scans it

for `#include` statements if we have not done so already. The content of the

include statement is pasted together with each provided `INCLUDE`

and checked to see if it forms the path to an existing or generated

source. If it does, then the following rules apply to determine

the language of the header file:



If the source including the header is a `CXX` source (including a `CXX`

header, and no other language has been set for this header, then

the language of the header is set to `CXX`



If any source including the header is a `C` source (including a `C` header)

then the language of the header is forced to "`C`", with one caveat:



The header file will be opened and scanned for any tokens which match

any provided tokens in `CPP_IDENTIFIERS` or `__cplusplus`. If it does, then

the header language will be set to `C;CXX`



* `SOURCE`: The source file to be scanned

* [Optional] `INCLUDES`: Any include directories to search for header files

* [Optional] `CPP_IDENTIFIERS`: Any identifiers which might indicate that this

                                source can be compiled with both C and CXX.



### `psq_determine_language_for_source` ###



Takes any source, including a header file and writes the determined

language into `LANGUAGE_RETURN`. If the source is a header file

`SOURCE_WAS_HEADER_RETURN` will be set to true as well.



This function only works for header files if those header files

were included by sources previously scanned by

`psq_scan_source_for_headers`. They must be scanned before

this function is called, otherwise this function will be unable

to determine the language of the source file and report an error.



* `SOURCE`: The source whose language is to be determined

* `LANGUAGE_RETURN`: A variable where the language can be written into

* `SOURCE_WAS_HEADER_RETURN`: A variable where a boolean variable, indicating

                              whether this was a header or a source that was

                              checked.

* [Optional] `FORCE_LANGUAGE`: Performs scanning, but forces language to be one

                               of `C` or `CXX`.