userdiff: support Bash

Support POSIX, bashism and mixed function declarations, all four
compound command types, trailing comments and mixed whitespace.

Even though Bash allows locale-dependent characters in function names
<https://unix.stackexchange.com/a/245336/3645>, only detect function
names with characters allowed by POSIX.1-2017
<https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_235>
for simplicity. This should cover the vast majority of use cases, and
produces system-agnostic results.

Since a word pattern has to be specified, but there is no easy way to
know the default word pattern, use the default `IFS` characters for a
starter. A later patch can improve this.

Signed-off-by: Victor Engmark <victor@engmark.name>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -802,6 +802,9 @@ patterns are available:
 
 - `ada` suitable for source code in the Ada language.
 
+- `bash` suitable for source code in the Bourne-Again SHell language.
+  Covers a superset of POSIX shell function definitions.
+
 - `bibtex` suitable for files with BibTeX coded references.
 
 - `cpp` suitable for source code in the C and C++ languages.

t/t4018-diff-funcname.sh

@@ -27,6 +27,7 @@ test_expect_success 'setup' '
 
 diffpatterns="
 	ada
+	bash
 	bibtex
 	cpp
 	csharp

t/t4018/bash-arithmetic-function

@@ -0,0 +1,4 @@
+RIGHT() ((
+
+    ChangeMe = "$x" + "$y"
+))

t/t4018/bash-bashism-style-compact

@@ -0,0 +1,6 @@
+function RIGHT {
+    function InvalidSyntax{
+        :
+        echo 'ChangeMe'
+    }
+}

t/t4018/bash-bashism-style-function

@@ -0,0 +1,4 @@
+function RIGHT {
+    :
+    echo 'ChangeMe'
+}

t/t4018/bash-bashism-style-whitespace

@@ -0,0 +1,4 @@
+	 function 	RIGHT 	( 	) 	{
+
+	    ChangeMe
+	 }

t/t4018/bash-conditional-function

@@ -0,0 +1,4 @@
+RIGHT() [[ \
+
+    "$a" > "$ChangeMe"
+]]

t/t4018/bash-missing-parentheses

@@ -0,0 +1,6 @@
+function RIGHT {
+    functionInvalidSyntax {
+        :
+        echo 'ChangeMe'
+    }
+}

t/t4018/bash-mixed-style-compact

@@ -0,0 +1,4 @@
+function RIGHT(){
+    :
+    echo 'ChangeMe'
+}

t/t4018/bash-mixed-style-function

@@ -0,0 +1,4 @@
+function RIGHT() {
+
+    ChangeMe
+}

t/t4018/bash-nested-functions

@@ -0,0 +1,6 @@
+outer() {
+    RIGHT() {
+        :
+        echo 'ChangeMe'
+    }
+}

t/t4018/bash-other-characters

@@ -0,0 +1,4 @@
+_RIGHT_0n() {
+
+    ChangeMe
+}

t/t4018/bash-posix-style-compact

@@ -0,0 +1,4 @@
+RIGHT(){
+
+    ChangeMe
+}

t/t4018/bash-posix-style-function

@@ -0,0 +1,4 @@
+RIGHT() {
+
+    ChangeMe
+}

t/t4018/bash-posix-style-whitespace

@@ -0,0 +1,4 @@
+	 RIGHT 	( 	) 	{
+
+	    ChangeMe
+	 }

t/t4018/bash-subshell-function

@@ -0,0 +1,4 @@
+RIGHT() (
+
+    ChangeMe=2
+)

t/t4018/bash-trailing-comment

@@ -0,0 +1,4 @@
+RIGHT() { # Comment
+
+    ChangeMe
+}

userdiff.c

@@ -23,6 +23,27 @@ IPATTERN("ada",
 	 "[a-zA-Z][a-zA-Z0-9_]*"
 	 "|[-+]?[0-9][0-9#_.aAbBcCdDeEfF]*([eE][+-]?[0-9_]+)?"
 	 "|=>|\\.\\.|\\*\\*|:=|/=|>=|<=|<<|>>|<>"),
+PATTERNS("bash",
+	 /* Optional leading indentation */
+	 "^[ \t]*"
+	 /* Start of captured text */
+	 "("
+	 "("
+	     /* POSIX identifier with mandatory parentheses */
+	     "[a-zA-Z_][a-zA-Z0-9_]*[ \t]*\\([ \t]*\\))"
+	 "|"
+	     /* Bashism identifier with optional parentheses */
+	     "(function[ \t]+[a-zA-Z_][a-zA-Z0-9_]*(([ \t]*\\([ \t]*\\))|([ \t]+))"
+	 ")"
+	 /* Optional whitespace */
+	 "[ \t]*"
+	 /* Compound command starting with `{`, `(`, `((` or `[[` */
+	 "(\\{|\\(\\(?|\\[\\[)"
+	 /* End of captured text */
+	 ")",
+	 /* -- */
+	 /* Characters not in the default $IFS value */
+	 "[^ \t]+"),
 PATTERNS("dts",
 	 "!;\n"
 	 "!=\n"