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I am using ctags to index fortran files for code navigation in Emacs with M-..

In doing so I have noticed that it doesn't recognize declarations of the form

MODULE PROCEDURE MySubroutineName   ! or
MODULE SUBROUTINE MySubRoutineName

which arise when using the SUBMODULE feature.

In "https://stackoverflow.com/questions/3497538/ctags-and-fortrans-interfaces" a similar issue occurred, but there the solution was merely to enable a feature, that isn't enabled by default. For submodules no such feature exists.

Is it possible to make ctags aware of this construct?

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ctags supports regular expression which could be used to parse tags.

Add below code into ~/.ctags,

--regex-fortran=/^[ \t]*MODULE[ \t]+(PROCEDURE|SUBROUTINE)[ \t]+([a-zA-Z0-9_]+)/\2/s,subroutines/

hello.f is like,

MODULE PROCEDURE MySubroutineName1   ! or
MODULE SUBROUTINE MySubRoutineName2

Then run ctags -e hello.f to test.

See https://duckduckgo.com/?q=ctags+regular+expression&t=ffab&atb=v202-1&ia=web on regular expression syntax.

Please note exuberant-ctags will load ~/.ctags by default but universal-ctags loads ~/.ctags.d/*.ctags instead of ~/.ctags. So you might need run ln -s ~/.ctags ~/.ctags.d/1.ctags if you replace exuberant-ctags with universal-ctags.

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The issue occurred, because ctags on my system was the "Exuberant Ctags" implementation, whose latest version is from 2009; The language feature I needed support for was standardized only in 2008.

I solved the issue by asking the administrator to install "Universal Ctags", which should be the best-maintained variant of ctags.


I'll leave this question open in the hope that someone knows a way to add support, when using a newer ctags implementation isn't possible (e.g. tight software guidelines in a company, or when encountering a feature not yet supported out of the box by any implementation).

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  • Through fixing is not promised, it is worth to make an issue at u-ctags's GitHub repo page. – Masatake YAMATO Mar 6 '20 at 20:57

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