non-declaration statements are permitted at top level

[adonovan]

A Go source file always starts with a package declaration, but the Tree Sitter grammar for Go permits statements at top level:

x = 1

[source_file](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [1, 0]
  [assignment_statement](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 5]
    left: [expression_list](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 1]
      [identifier](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 1]
    right: [expression_list](https://tree-sitter.github.io/tree-sitter/playground#) [0, 4] - [0, 5]
      [int_literal](https://tree-sitter.github.io/tree-sitter/playground#) [0, 4] - [0, 5]

x := <-ch

[source_file](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [1, 0]
  [short_var_declaration](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 9]
    left: [expression_list](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 1]
      [identifier](https://tree-sitter.github.io/tree-sitter/playground#) [0, 0] - [0, 1]
    right: [expression_list](https://tree-sitter.github.io/tree-sitter/playground#) [0, 5] - [0, 9]
      [unary_expression](https://tree-sitter.github.io/tree-sitter/playground#) [0, 5] - [0, 9]
        operand: [identifier](https://tree-sitter.github.io/tree-sitter/playground#) [0, 7] - [0, 9]

The cause is this production:

tree-sitter-go/grammar.js

Lines 105 to 108 in 07d7228

	source_file: $ => repeat(choice(
	seq($._statement, terminator),
	seq($._top_level_declaration, optional(terminator)),
	)),

The fix is to remove the reference to _statement here and to add _declaration (var/const/type) to the choices for _top_level_declaration:

tree-sitter-go/grammar.js

Lines 110 to 115 in 07d7228

	_top_level_declaration: $ => choice(
	$.package_clause,
	$.function_declaration,
	$.method_declaration,
	$.import_declaration
	),

I wonder whether this was done intentionally because some tools want to process a chunk of statements instead of a complete file.

[maxbrunsfeld]

This is intentional, so that Tree-sitter can parse things like code snippets inside of markdown files.