fix: remove variable_definition and assignment rules from pipeline

[guilhas07]

Problem

Rules like variable_definition, assignment, range_action,
template_action, block_action, chained_pipeline, argument_list
incorrectly allowed for variable definitions and assignments inside
them.

Solution

Remove rules variable_definition and assignment from
pipeline, using a new rule where both are supported.

---

Go parser doesn't error for variables definitions, assignments inside block and
chain operations, despite not working. So I couldn't create a invalid tests
for those cases.

Examples that don't trigger a parsing error:

{{block "name" $var1 := "test"}} T1 {{ end }} -> Correction: This is valid
{{ $var := 5 | print }} -> This is also a valid variable declaration...

We can hack it by mentioning the variable like so:

{{block "name" $var := 5}} {{$var}} {{end}}
{{ $var := 5 | print $var }}

but at this point I don't think it is worth it.

[qvalentin]

I'm not sure about the point about block nodes, it does work, if you access the variable after the block:

{{ $var1 := 2 }}
{{block "name" $var1 = "test"}} T1 {{ end }}
{{ print $var1 }}

We should try to be aligned with the parser of gotemplate and not assume additional logic.

[guilhas07]

I'm not sure about the point about block nodes, it does work, if you access the variable after the block:

{{ $var1 := 2 }}
{{block "name" $var1 = "test"}} T1 {{ end }}
{{ print $var1 }}

We should try to be aligned with the parser of gotemplate and not assume additional logic.

I only tried to access the variable inside the block and not outside, so I completely missed that. Was my understanding also incorrect in the chained pipeline case?

Edit: My example is a valid variable declaration. So a better example would be a variable declaration in the middle of a chained pipeline.

[qvalentin]

Technically this should be allowed:

{{ $var := 2 | print }} 

But it would require more changes in the chained pipeline rule.

[qvalentin]

Very interesting,

this is not allowed:

{{ $var:=list }}
{{range $var=list}} t1 {{ end }}

But this is (even executes):

{{range $var:=list}} t1 {{ end }}

[guilhas07]

Yeah, the second is an element range. I added support for that in #32

[qvalentin]

Should be called Invalid function parameters.

Also the same thing with with variable definition could be added:

{{ print $var:=5 }}

[guilhas07]

Technically this should be allowed:

{{ $var := 2 | print }} 

But it would require more changes in the chained pipeline rule.

I think it already is supported:

tree-sitter-go-template/test/corpus/examples.txt

Lines 135 to 151 in 5f19a36

	====================================
	A with action that creates and uses a variable.
	====================================
	{{with $x := "output" | printf "%q"}}{{$x}}{{end}}
	---
	(template
	(with_action
	(variable_definition
	(variable (identifier))
	(chained_pipeline
	(interpreted_string_literal)
	(function_call
	(identifier)
	(argument_list
	(interpreted_string_literal)))))
	(variable (identifier))))