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>

5 files changed, 25 insertions, 0 deletions

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
+}