Jsx ast

[nojaf]

This is a part of #7283.
I'm introducing Pexp_jsx_fragment to represent fragment syntax <></>.

I found it insightful to just try it out and see what code changes are necessary.

In short a fragment is now parsed as:

        expression 
          attribute  "JSX"
            []
          Pexp_construct "::" 
          Some
            expression 
              Pexp_tuple
              [
                expression 
                  attribute  "JSX"
                    []
                  Pexp_apply
                  expression 
                    Pexp_ident "SectionHeader.createElement" 
                  [
                    <arg>
                    Labelled "children"
                      expression 
                        Pexp_construct "::" 
                        Some
                          expression 
                            Pexp_tuple
                            [
                              expression 
                                attribute  "res.braces"
                                  []
                                Pexp_apply
                                expression 
                                  Pexp_ident "React.string" 
                                [
                                  <arg>
                                  Nolabel
                                    expression 
                                      Pexp_constant PConst_string ("abc",Some "*j")
                                ]
                              expression 
                                Pexp_construct "[]" 
                                None
                            ]
                    <arg>
                    Nolabel
                      expression 
                        Pexp_construct "()" 
                        None
                  ]
                expression 
                  Pexp_construct "[]" 
                  None
              ]

after this change it becomes:

        expression 
          Pexp_jsx_fragment          [
            expression 
              attribute  "JSX"
                []
              Pexp_apply
              expression 
                Pexp_ident "SectionHeader.createElement" 
              [
                <arg>
                Labelled "children"
                  expression 
                    Pexp_construct "::" 
                    Some
                      expression 
                        Pexp_tuple
                        [
                          expression 
                            attribute  "res.braces"
                              []
                            Pexp_apply
                            expression 
                              Pexp_ident "React.string" 
                            [
                              <arg>
                              Nolabel
                                expression 
                                  Pexp_constant PConst_string ("abc",Some "*j")
                            ]
                          expression 
                            Pexp_construct "[]" 
                            None
                        ]
                <arg>
                Nolabel
                  expression 
                    Pexp_construct "()" 
                    None
              ]
          ]

I'll add some comment to relevant changes.

[nojaf]

I prefer ranges to be accurate. The location should start at the opening < token.

[nojaf]

@shulhi this part isn't 100% correct.
I'm not familiar enough with this part of the codebase.

let z1 = <> <SectionHeader> {React.string("abc")} </SectionHeader> </>

will be formatted to

let z1 =
<>
  <SectionHeader> {React.string("abc")} </SectionHeader>
</>

so I'm missing some indent here. Not sure how that part works.
Would love to hear your thoughts on this.

[shulhi]

@nojaf I checked, the indentation is handled here,

rescript/compiler/syntax/src/res_printer.ml

Lines 2085 to 2103 in 9da9b19

	let should_indent =
	match opt_braces with
	| Some _ -> false
	| _ -> (
	ParsetreeViewer.is_binary_expression expr
	||
	match vb.pvb_expr with
	| {
	pexp_attributes = [({Location.txt = "res.ternary"}, _)];
	pexp_desc = Pexp_ifthenelse (if_expr, _, _);
	} ->
	ParsetreeViewer.is_binary_expression if_expr
	|| ParsetreeViewer.has_attributes if_expr.pexp_attributes
	| {pexp_desc = Pexp_newtype _} -> false
	| {pexp_attributes = [({Location.txt = "res.taggedTemplate"}, _)]} ->
	false
	| e ->
	ParsetreeViewer.has_attributes e.pexp_attributes
	|| ParsetreeViewer.is_array_access e)

You might need to handle the case for Pexp_jsx_fragment here.

[nojaf]

Thanks, the old code will instead have matched ParsetreeViewer.has_attributes e.pexp_attributes. Indentation now works as before.

[nojaf]

Changes like this are to be expected as the range of a fragment spans from <> till end </>.

[nojaf]

This ghost expression is a part of the AstHelper.make_list_expression result.
It is no longer present in the new AST, but it also didn't serve any purpose.
I believe it is okay that this test is slightly different.
In the end the result didn't change.

[nojaf]

The reason the store the > and </ token is this edge case:
https://rescript-lang.org/try?version=v12.0.0-alpha.8&module=esmodule&code=DYUwLgBA+hC8ECgCQAeCB6AVBAzmATgIYB2A5iBJuhAHzJIDeASiIQMZgB0e+AlmQAoARAFsQACyEBKAL7IU1LBEIiIASQh9S4yFVpA

If we ever want to restore comments I suppose we need the proper anchors.

[nojaf]

@shulhi I believe the comment capture isn't working here for:

let _ =
  <> // foobar

  {React.string("m")}
  {React.int(4)}
  </>

I got nothing for:

dune exec res_parser -- A.res -print comments
leading comments:                        

comments inside:

trailing comments: