diff: funcname and word patterns for perl

The default function name discovery already works quite well for Perl
code... with the exception of here-documents (or rather their ending).

 sub foo {
	print <<END
 here-document
 END
	return 1;
 }

The default funcname pattern treats the unindented END line as a
function declaration and puts it in the @@ line of diff and "grep
--show-function" output.

With a little knowledge of perl syntax, we can do better.  You can
try it out by adding "*.perl diff=perl" to the gitattributes file.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -494,6 +494,8 @@ patterns are available:
 
 - `pascal` suitable for source code in the Pascal/Delphi language.
 
+- `perl` suitable for source code in the Perl language.
+
 - `php` suitable for source code in the PHP language.
 
 - `python` suitable for source code in the Python language.

t/t4018-diff-funcname.sh

@@ -32,7 +32,7 @@ EOF
 
 sed 's/beer\\/beer,\\/' < Beer.java > Beer-correct.java
 
-builtin_patterns="bibtex cpp csharp fortran html java objc pascal php python ruby tex"
+builtin_patterns="bibtex cpp csharp fortran html java objc pascal perl php python ruby tex"
 for p in $builtin_patterns
 do
 	test_expect_success "builtin $p pattern compiles" '

userdiff.c

@@ -61,6 +61,21 @@ PATTERNS("pascal",
 	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
 	 "|<>|<=|>=|:=|\\.\\."
 	 "|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("perl",
+	 "^[ \t]*package .*;\n"
+	 "^[ \t]*sub .* \\{",
+	 /* -- */
+	 "[[:alpha:]_'][[:alnum:]_']*"
+	 "|0[xb]?[0-9a-fA-F_]*"
+	 /* taking care not to interpret 3..5 as (3.)(.5) */
+	 "|[0-9a-fA-F_]+(\\.[0-9a-fA-F_]+)?([eE][-+]?[0-9_]+)?"
+	 "|=>|-[rwxoRWXOezsfdlpSugkbctTBMAC>]|~~|::"
+	 "|&&=|\\|\\|=|//=|\\*\\*="
+	 "|&&|\\|\\||//|\\+\\+|--|\\*\\*|\\.\\.\\.?"
+	 "|[-+*/%.^&<>=!|]="
+	 "|=~|!~"
+	 "|<<|<>|<=>|>>"
+	 "|[^[:space:]]"),
 PATTERNS("php",
 	 "^[\t ]*(((public|protected|private|static)[\t ]+)*function.*)$\n"
 	 "^[\t ]*(class.*)$",