xtext: How to format code where block needs to be indented - formatting

Question

My grammar is given by:
Model:
'module' (mn=ID)?
(func+=Function)+
'end_module'
;
Function:
'function' name=ID '('')'
(vars+=ID)*
'end_function'
;
I can find the token like 'function', '(' etc.
How can If force a new line after the token 'module' if the optional data mn does not exist and after mn if it does exist?
How can I indent the block begin 'module' and 'end_module' as well as 'function' and 'end_function'?
The formatting I am looking for:
module test
function fdf ()
str1
str2
end_function
function ff ()
end_function
end_module
So far I do generate the formatting stubs by using:
formatter = {
generateStub = true
}

Answer 1

that should be rather straight forward e.g.
#Inject extension MyDslGrammarAccess
def dispatch void format(Model model, extension IFormattableDocument document) {
model.regionFor.keyword(modelAccess.end_moduleKeyword_3).prepend[newLine]
if (model.mn != null) {
model.regionFor.feature(MyDslPackage.Literals.MODEL__MN).append[newLine]
interior(
model.regionFor.feature(MyDslPackage.Literals.MODEL__MN),
model.regionFor.keyword(modelAccess.end_moduleKeyword_3)
) [indent]
} else {
model.regionFor.keyword(modelAccess.moduleKeyword_0).append[newLine]
interior(
model.regionFor.keyword(modelAccess.moduleKeyword_0),
model.regionFor.keyword(modelAccess.end_moduleKeyword_3)
) [indent]
}
for (Function func : model.getFunc()) {
func.format;
}
}
def dispatch void format(Function function, extension IFormattableDocument document) {
function.regionFor.keyword(functionAccess.functionKeyword_0).append[newLine].prepend[newLine]
function.regionFor.keyword(functionAccess.end_functionKeyword_5).prepend[newLine]
interior(
function.regionFor.keyword(functionAccess.functionKeyword_0),
function.regionFor.keyword(functionAccess.end_functionKeyword_5)
) [indent]
}

Answer 2

As proposed in Max's Answer, it is possible to cope with whitespace-aware languages starting from Xtext v2.8. Check it out!.
In your case, I guess you should define your grammar as follows:
Model:
'module' (mn=ID)?
BEGIN
(func+=Function)+
END
'end_module'
;
Function:
'function' name=ID '('')'
BEGIN
(vars+=ID)*
END
'end_function'
;
terminal BEGIN: 'synthetic:BEGIN';
terminal END: 'synthetic:END';
In case you would also want to allow 'empty-bodied' functions, I guess you should change the rule above as follows:
Function:
'function' name=ID '('')'
(BEGIN
(vars+=ID)*
END)?
'end_function'
;
Hope it helps!