Perf: Reuse AST passed from bultin:swc_loader to avoid double parse

[hardfist]

span is not valid after transformation

currrently Rspack will do double parse for all file processed by builtin:swc-loader, the reason Rspack do double parse is caused by swc transform will make the origin span invalid which cause it's bad for following dependency generation

• before transformed by builtin:swc-loader

import { b }  from './b';
const  a = b;  // now AstNode('b') span is 37-38

• after transformed by builtin:swc-loader

import { b }  from './b';
var a = b; // the span in ast is still 37-38 but after codegen the valid span is actually 34-35

span can be fixed by srcmapbuf generated by codegen

so the span in ASTNode is not valid after transformation, but we can fix the span use src_map generated by emitter, the src_map contains the right mapping from span in ast to span after codegen

rspack/crates/rspack_plugin_javascript/src/ast/stringify.rs

Lines 79 to 84 in 9112e35

	let mut wr = Box::new(text_writer::JsWriter::new(
	source_map.clone(),
	"\n",
	&mut buf,
	source_map_config.enable.then_some(&mut src_map_buf),
	)) as Box<dyn WriteJs>;

we fix ast span using visit_mut_span in SpanFixerVisitor

struct SpanFixerVisitor {
   src_map_buf: SrcMapBuf
};
impl VisitMut for SpanFixerVisitor {
   fn visit_mut_span(&mut self, span: &mut Span){
             let codegen_span = self.src_map_buf.get(span);
             span.start = codegen_span.start;
             span.end = codegen_span.end;
   }
}

ast invalidation

we should mark the ast dirty | invalid, if the code is modified by following loader

reuse span in module.build

if the AST contains the valid span, then parse can reuse ast passing from builtin:swc-loader, no need to do double parse in module.build

rspack/crates/rspack_core/src/normal_module.rs

Line 542 in 9112e35

source: original_source.clone(),

[GiveMe-A-Name]

Except fix the span, we need pass ast from swc_loader to JavaScriptParserAndGenerator.
We can use additional_data: anymap::Map<dyn CloneAny + Send + Sync> to pass ast.

// swc_loader
fn run(loader_context) {
 ....
 let mut additional_data = Default::default();
 additional_data.insert(ast);
 
 loader_context.finish((code, map, additional_data))
}

then get ast from additional_data

// parser_and_generator
fn parse(parse_context) {
   let ParseContext { additional_data } = parse_context;

   let ast = additional_data.get::<SwcAst>();

   ....
}

[h-a-n-a]

We can use additional_data: anymap::Map<dyn CloneAny + Send + Sync> to pass ast.

Voting for this solution.

Given the status-quo, AdditionalData is replaced by each loader, so there's no need to introduce the mental model to even invalidating the AST.

[GiveMe-A-Name]

Actually, we can't get mapping that from source span to transformed span using src_map_buf.
The src_map_buf is used for generate source_map, It only maps a portion of the span's start or end positions to the corresponding source line and column numbers.
We need other way.