userdiff: add built-in pattern for golang

This adds xfuncname and word_regex patterns for golang, a quite
popular programming language. It also includes test cases for the
xfuncname regex (t4018) and updated documentation.

The xfuncname regex finds functions, structs and interfaces.  Although
the Go language prohibits the opening brace from being on its own
line, the regex does not makes it mandatory, to be able to match
`func` statements like this:

    func foo(bar int,
    	baz int) {
    }

This is covered by the test case t4018/golang-long-func.

The word_regex pattern finds identifiers, integers, floats, complex
numbers and operators, according to the go specification.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

8 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index c21f5ca109..d52b254a22 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -714,6 +714,8 @@ patterns are available:
 
 - `fountain` suitable for Fountain documents.
 
+- `golang` suitable for source code in the Go language.
+
 - `html` suitable for HTML/XHTML documents.
 
 - `java` suitable for source code in the Java language.
diff --git a/t/t4018-diff-funcname.sh b/t/t4018-diff-funcname.sh
index 1795ffc3aa..22f9f88f0a 100755
--- a/t/t4018-diff-funcname.sh
+++ b/t/t4018-diff-funcname.sh
@@ -33,6 +33,7 @@ diffpatterns="
 	css
 	fortran
 	fountain
+	golang
 	html
 	java
 	matlab
diff --git a/t/t4018/golang-complex-function b/t/t4018/golang-complex-function
new file mode 100644
index 0000000000..e057dcefed
--- /dev/null
+++ b/t/t4018/golang-complex-function
@@ -0,0 +1,8 @@
+type Test struct {
+	a Type
+}
+
+func (t *Test) RIGHT(a Type) (Type, error) {
+	t.a = a
+	return ChangeMe, nil
+}
diff --git a/t/t4018/golang-func b/t/t4018/golang-func
new file mode 100644
index 0000000000..8e9c9ac7c3
--- /dev/null
+++ b/t/t4018/golang-func
@@ -0,0 +1,4 @@
+func RIGHT() {
+	a := 5
+	b := ChangeMe
+}
diff --git a/t/t4018/golang-interface b/t/t4018/golang-interface
new file mode 100644
index 0000000000..553bedec96
--- /dev/null
+++ b/t/t4018/golang-interface
@@ -0,0 +1,4 @@
+type RIGHT interface {
+	a() Type
+	b() ChangeMe
+}
diff --git a/t/t4018/golang-long-func b/t/t4018/golang-long-func
new file mode 100644
index 0000000000..ac3a77b5c4
--- /dev/null
+++ b/t/t4018/golang-long-func
@@ -0,0 +1,5 @@
+func RIGHT(aVeryVeryVeryLongVariableName AVeryVeryVeryLongType,
+	anotherLongVariableName AnotherLongType) {
+	a := 5
+	b := ChangeMe
+}
diff --git a/t/t4018/golang-struct b/t/t4018/golang-struct
new file mode 100644
index 0000000000..5deda77fee
--- /dev/null
+++ b/t/t4018/golang-struct
@@ -0,0 +1,4 @@
+type RIGHT struct {
+	a Type
+	b ChangeMe
+}
diff --git a/userdiff.c b/userdiff.c
index dbfb4e13cd..8f5028f6b2 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -38,6 +38,15 @@ IPATTERN("fortran",
 	 "|//|\\*\\*|::|[/<>=]="),
 IPATTERN("fountain", "^((\\.[^.]|(int|ext|est|int\\.?/ext|i/e)[. ]).*)$",
 	 "[^ \t-]+"),
+PATTERNS("golang",
+	 /* Functions */
+	 "^[ \t]*(func[ \t]*.*(\\{[ \t]*)?)\n"
+	 /* Structs and interfaces */
+	 "^[ \t]*(type[ \t].*(struct|interface)[ \t]*(\\{[ \t]*)?)",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.eE]+i?|0[xX]?[0-9a-fA-F]+i?"
+	 "|[-+*/<>%&^|=!:]=|--|\\+\\+|<<=?|>>=?|&\\^=?|&&|\\|\\||<-|\\.{3}"),
 PATTERNS("html", "^[ \t]*(<[Hh][1-6]([ \t].*)?>.*)$",
 	 "[^<>= \t]+"),
 PATTERNS("java",