evalR(): each message() results in an extra newline

[HenrikBengtsson]

Example

$ cat ./webR-message-newline.mjs

#! /usr/bin/env node
import { WebR } from "webr";
import WebSocket from "ws";

console.log('Node.js v', process.version);

// Launch webR instance
const webR = new WebR();
await webR.init();
console.log("webR v" + webR.version);

const code = `
cat("----------------------\n")
cat("abc")
cat("def")
cat("\n")
cat("ABC\n")
cat("DEF\n")
cat("----------------------\n")
message("abc", appendLF = FALSE)
message("def", appendLF = FALSE)
message("ABC\n", appendLF = FALSE)
message("DEF\n", appendLF = FALSE)
cat("----------------------\n")
message("abc", appendLF = TRUE)
message("def", appendLF = TRUE)
message("ABC\n", appendLF = TRUE)
message("DEF\n", appendLF = TRUE)
cat("----------------------\n")
`;

await webR.evalR(code);

process.exit(0);

gives

$ ./webR-message-newline.mjs
Node.js v v22.19.0
webR v0.5.6
----------------------
abcdef
ABC
DEF
----------------------
abc
def
ABC

DEF

----------------------
abc

def

ABC


DEF


----------------------

but I'd expect:

----------------------
abcdef
ABC
DEF
----------------------
abcdefABC
DEF
----------------------
abc
def
ABC

DEF

----------------------