Add `--script-dump-ast` command line argument to output an AST of a GDScript file

[Calinou]

• Related to https://github.com/godotengine/godot-proposals/issues/3069 and https://github.com/godotengine/godot-proposals/issues/3630.

Describe the project you are working on

The Godot editor :slightly_smiling_face:

Describe the problem or limitation you are having in your project

Third-party tools wishing to work with GDScript have to implement their own parser. This applies to linters, formatters and code analysis tools.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

We can avoid the requirement for third-party tools to reimplement a parser by allowing Godot to dump an AST (Abstract Syntax Tree) of any given script.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Add a --script-dump-ast <path to script> command line argument that prints the AST to standard output and quits Godot afterwards. To prevent a window from being visible, --headless is implied when using --script-dump-ast.

This standard output can then be redirected to a file by the user to write the AST to a file. The output format should preferably be something standard and easy to parse by other tools, such as JSON.

If there is a need to dump multiple ASTs from a single engine run (to make dumping several scripts faster), we can allow multiple paths separated by spaces (so it works with globbing as well). In this case, each dump should be its own JSON document so they can be cleanly separated, and each dump should contain the path to the script (relative to the project root).

Example output from a Clang AST dump (clang-check -ast-dump test.c --extra-arg="-fno-color-diagnostics" --):

#include <stdio.h>
#include <stdlib.h>

int main() {
	printf("Hello world!");
	return EXIT_SUCCESS;
}

`-FunctionDecl 0x5647b82497d0 </home/hugo/test.c:4:1, line:7:1> line:4:5 main 'int ()'
  `-CompoundStmt 0x5647b82499d8 <col:12, line:7:1>
    |-CallExpr 0x5647b8249950 <line:5:2, col:23> 'int'
    | |-ImplicitCastExpr 0x5647b8249938 <col:2> 'int (*)(const char *, ...)' <FunctionToPointerDecay>
    | | `-DeclRefExpr 0x5647b8249870 <col:2> 'int (const char *, ...)' Function 0x5647b81d6fe8 'printf' 'int (const char *, ...)'
    | `-ImplicitCastExpr 0x5647b8249990 <col:9> 'const char *' <NoOp>
    |   `-ImplicitCastExpr 0x5647b8249978 <col:9> 'char *' <ArrayToPointerDecay>
    |     `-StringLiteral 0x5647b82498c8 <col:9> 'char[13]' lvalue "Hello world!"
    `-ReturnStmt 0x5647b82499c8 <line:6:2, /usr/include/stdlib.h:93:22>
      `-IntegerLiteral 0x5647b82499a8 <col:22> 'int' 0

If this enhancement will not be used often, can it be worked around with a few lines of script?

No.

Is there a reason why this should be core and not an add-on in the asset library?

This is about improving interoperability with third-party utilities not made with Godot.