span_to_source is extremely inefficient for Wasm plugins

[kdy1]

Instead of passing only a string, we send the whole SourceFile twice.

swc/crates/swc_plugin_proxy/src/source_map/plugin_source_map_proxy.rs

Lines 130 to 139 in 1bf9b37

	let local_begin: SourceFileAndBytePos =
	read_returned_result_from_host_fallible(|serialized_ptr| unsafe {
	__lookup_byte_offset_proxy(sp.lo().0, serialized_ptr)
	})
	.expect("Should return begin offset");
	let local_end: SourceFileAndBytePos =
	read_returned_result_from_host_fallible(|serialized_ptr| unsafe {
	__lookup_byte_offset_proxy(sp.hi().0, serialized_ptr)
	})
	.expect("Should return end offset");

This makes span_to_string extremely slow when the input is large.

Found while working on #6404

[kwonoj]

ugh looks like caching attempt only local to host side, not skipping to sending to guest with serialization

swc/crates/swc_plugin_runner/src/imported_fn/source_map.rs

Line 58 in 1bf9b37

Some(original_loc.file)

Probably better / correct way is skipping to include originalLoc if guest already allocated same sourceFile.

[swc-bot]

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