userdiff: extend Bash pattern to cover more shell function forms

The previous function regex required explicit matching of function
bodies using `{`, `(`, `((`, or `[[`, which caused several issues:

- It failed to capture valid functions where `{` was on the next line
  due to line continuation (`\`).
- It did not recognize functions with single  command body, such as
  `x () echo hello`.

Replacing the function body matching logic with `.*$`, ensures
that everything on the function definition line is captured.

Additionally, the word regex is refined to better recognize shell
syntax, including additional parameter expansion operators and
command-line options.

Signed-off-by: Moumita Dhar <dhar61595@gmail.com>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4018/bash-bashism-style-complete-line-capture

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

t/t4018/bash-posix-style-complete-line-capture

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

t/t4018/bash-posix-style-single-command-function

@@ -0,0 +1,3 @@
+RIGHT() echo "hello"
+
+    ChangeMe

t/t4034-diff-words.sh

@@ -320,6 +320,7 @@ test_expect_success 'unset default driver' '
 
 test_language_driver ada
 test_language_driver bibtex
+test_language_driver bash
 test_language_driver cpp
 test_language_driver csharp
 test_language_driver css

t/t4034/bash/expect

@@ -0,0 +1,36 @@
+<BOLD>diff --git a/pre b/post<RESET>
+<BOLD>index 09ac008..60ba6a2 100644<RESET>
+<BOLD>--- a/pre<RESET>
+<BOLD>+++ b/post<RESET>
+<CYAN>@@ -1,31 +1,31 @@<RESET>
+<RED>my_var<RESET><GREEN>new_var<RESET>=10
+x=<RED>123<RESET><GREEN>456<RESET>
+echo <RED>$1<RESET><GREEN>$2<RESET>
+echo <RED>$USER<RESET><GREEN>$USERNAME<RESET>
+${<RED>HOME<RESET><GREEN>HOMEDIR<RESET>}
+((a<RED>+<RESET><GREEN>+=<RESET>b))
+((a<RED>*<RESET><GREEN>*=<RESET>b))
+((a<RED>/<RESET><GREEN>/=<RESET>b))
+((a<RED>%<RESET><GREEN>%=<RESET>b))
+((a<RED>|<RESET><GREEN>|=<RESET>b))
+((a<RED>^<RESET><GREEN>^=<RESET>b))
+((a<RED>=<RESET><GREEN>==<RESET>b))
+((a<RED>!<RESET><GREEN>!=<RESET>b))
+((a<RED><<RESET><GREEN><=<RESET>b))
+((a<RED>><RESET><GREEN>>=<RESET>b))
+$((a<RED><<RESET><GREEN><<<RESET>b))
+$((a<RED>><RESET><GREEN>>><RESET>b))
+$((a<RED>&<RESET><GREEN>&&<RESET>b))
+$((a<RED>|<RESET><GREEN>||<RESET>b))
+${a<RED>:<RESET><GREEN>:-<RESET>b}
+${a<RED>:<RESET><GREEN>:=<RESET>b}
+${a<RED>:<RESET><GREEN>:+<RESET>b}
+${a<RED>:<RESET><GREEN>:?<RESET>b}
+${a<RED>#<RESET><GREEN>##<RESET>*/}
+${a<RED>%<RESET><GREEN>%%<RESET>.*}
+${a<RED>^<RESET><GREEN>^^<RESET>}
+${a<RED>,<RESET><GREEN>,,<RESET>}
+${<GREEN>!<RESET>a}
+${a[<RED>*<RESET><GREEN>@<RESET>]}
+ls <RED>-a<RESET><GREEN>-x<RESET>
+ls <RED>--all<RESET><GREEN>--color<RESET>

t/t4034/bash/post

@@ -0,0 +1,31 @@
+new_var=10
+x=456
+echo $2
+echo $USERNAME
+${HOMEDIR}
+((a+=b))
+((a*=b))
+((a/=b))
+((a%=b))
+((a|=b))
+((a^=b))
+((a==b))
+((a!=b))
+((a<=b))
+((a>=b))
+$((a<<b))
+$((a>>b))
+$((a&&b))
+$((a||b))
+${a:-b}
+${a:=b}
+${a:+b}
+${a:?b}
+${a##*/}
+${a%%.*}
+${a^^}
+${a,,}
+${!a}
+${a[@]}
+ls -x
+ls --color

t/t4034/bash/pre

@@ -0,0 +1,31 @@
+my_var=10
+x=123
+echo $1
+echo $USER
+${HOME}
+((a+b))
+((a*b))
+((a/b))
+((a%b))
+((a|b))
+((a^b))
+((a=b))
+((a!b))
+((a<b))
+((a>b))
+$((a<b))
+$((a>b))
+$((a&b))
+$((a|b))
+${a:b}
+${a:b}
+${a:b}
+${a:b}
+${a#*/}
+${a%.*}
+${a^}
+${a,}
+${a}
+${a[*]}
+ls -a
+ls --all

userdiff.c

@@ -59,20 +59,30 @@ PATTERNS("bash",
 	 "("
 	 "("
 	     /* POSIX identifier with mandatory parentheses */
-	     "[a-zA-Z_][a-zA-Z0-9_]*[ \t]*\\([ \t]*\\))"
+	     "([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]+))"
+	     "(function[ \t]+[a-zA-Z_][a-zA-Z0-9_]*(([ \t]*\\([ \t]*\\))|([ \t]+)))"
 	 ")"
-	 /* Optional whitespace */
+	 /* Everything after the function header is captured  */
-	 "[ \t]*"
+	 ".*$"
-	 /* Compound command starting with `{`, `(`, `((` or `[[` */
-	 "(\\{|\\(\\(?|\\[\\[)"
 	 /* End of captured text */
 	 ")",
 	 /* -- */
-	 /* Characters not in the default $IFS value */
+	 /* Identifiers: variable and function names */
-	 "[^ \t]+"),
+	  "[a-zA-Z_][a-zA-Z0-9_]*"
+	 /* Shell variables: $VAR, ${VAR} */
+	  "|\\$[a-zA-Z0-9_]+|\\$\\{"
+	  /*Command list separators and redirection operators  */
+	 "|\\|\\||&&|<<|>>"
+	 /* Operators ending in '=' (comparison + compound assignment) */
+	 "|==|!=|<=|>=|[-+*/%&|^]="
+	 /* Additional parameter expansion operators */
+	 "|:=|:-|:\\+|:\\?|##|%%|\\^\\^|,,"
+	 /* Command-line options (to avoid splitting -option) */
+	 "|[-a-zA-Z0-9_]+"
+	 /* Brackets and grouping symbols */
+	 "|\\(|\\)|\\{|\\}|\\[|\\]"),
 PATTERNS("bibtex",
 	 "(@[a-zA-Z]{1,}[ \t]*\\{{0,1}[ \t]*[^ \t\"@',\\#}{~%]*).*$",
 	 /* -- */