bug#13549: 24.3.50; FR: Improve grep output (show function names, when possible)

[Juri Linkov <juri@jurta.org>]

> FR: Improve grep output (show function names, when possible)

I think external commands (like `cscope' etc.) should output function names
much more efficiently than using `find-file-noselect' and `which-function'
to post-process their output.

There was a suggestion to implement this in `grep' with the
`-p --show-c-function' command line argument as mentioned in:

http://stackoverflow.com/questions/6133989/what-grep-command-will-include-the-current-function-name-in-its-output

There are other grep-like commands that already can output function names,
e.g. `git-grep'.  If you add to ~./.gitconfig the following lines:

[diff "el"]
        xfuncname = "^(\\(.*)$"

and to a project-specific file .gitattributes:

*.el   diff=el

then the following command will output function names:

git grep -inH -p -e "org-element-map"
lisp/org/org.el=20969=(defun org-fill-paragraph (&optional justify)
lisp/org/org.el:21047:		      (org-element-map

Since line numbers of function names are enclosed with `=' in its output,
they could be highlighted like `-' separators with this patch:

=== modified file 'lisp/progmodes/grep.el'
--- lisp/progmodes/grep.el	2013-05-18 16:32:43 +0000
+++ lisp/progmodes/grep.el	2013-05-22 20:36:00 +0000
@@ -410,7 +410,7 @@ (defvar grep-mode-font-lock-keywords
       (0 '(face nil compilation-message nil help-echo nil mouse-face nil) t)
       (1 grep-error-face)
       (2 grep-error-face nil t))
-     ("^.+?-[0-9]+-.*\n" (0 grep-context-face)))
+     ("^.+?[-=][0-9]+[-=].*\n" (0 grep-context-face)))
    "Additional things to highlight in grep output.
 This gets tacked on the end of the generated expressions.")
 

=== modified file 'etc/grep.txt'
--- etc/grep.txt	2013-01-03 00:36:36 +0000
+++ etc/grep.txt	2013-05-22 20:36:33 +0000
@@ -72,6 +72,14 @@
 agrep -n "INFO tree" ../info/*
 ../info/dir: 6: File: dir	Node: Top	This is the top of the INFO tree
 
+* git-grep
+  with `[diff "el"] xfuncname = "^(\\(.*)$"' in .gitconfig
+  and `*.el diff=el' in .gitattributes
+
+git grep -inH -p -e "org-element-map"
+lisp/org/org.el=20969=(defun org-fill-paragraph (&optional justify)
+lisp/org/org.el:21047:		      (org-element-map
+
 * unknown greps