Ability to change the root rule at runtime

[XVilka]

Inspired by the issue in C grammar: tree-sitter/tree-sitter-c#65

Currently parser is only able to successfully parse terminated statements, like:

const char * myarray[25];

But if you feed something like

const char * [25]

or

const char *

It emits an error.
It would be beneficial to support parsing such statements too.
@thestr4ng3r proposed the following change in the grammar:

diff --git a/grammar.js b/grammar.js
index 6a5fa25..5dc99a3 100644
--- a/grammar.js
+++ b/grammar.js
@@ -51,6 +51,7 @@ module.exports = grammar({
  word: $ => $.identifier,

  rules: {
+    the_actual_root: $ => $.type_descriptor,
    translation_unit: $ => repeat($._top_level_item),

    _top_level_item: $ => choice(

but it breaks many other cases

To clarify, what we actually need is in addition to parsing a full translation_unit like int a() { x = (const char *[25])y; }, in the same >application parse only the part inside the cast like const char *[25], which is type_descriptor.

So essentially, we would need a way to change the root rule to use at runtime, which isn't really tree-sitter-c specific. I wonder if >that is even theoretically possible with how the code generator works.

[ahlinc]

This is the known limitation for now.

• Multiple entry points? #870 - Multiple entry points? (main tracking issue)
• Allow an alternative start rule to be selected at runtime, and expose this feature in unit tests #711 - Allow an alternative start rule to be selected at runtime, and expose this feature in unit tests
• Parse a single expression in middle of file? #950 - Parse a single expression in middle of file?