bug: deno test --doc incorrectly evaluates snippets

[iuioiua]

To reproduce:

1. git clone https://github.com/denoland/std.git
2. Run deno test --doc log/mod.ts using latest canary and get the following:

error: TS2304 [ERROR]: Cannot find name 'logger'.
    logger.debug(`running ${a} + ${b}`);
    ~~~~~~
    at file:///Users/asher/GitHub/std/log/mod.ts$121-131.ts:3:5

TS2304 [ERROR]: Cannot find name 'logger'.
    logger().debug(`running ${a} + ${b}`);
    ~~~~~~
    at file:///Users/asher/GitHub/std/log/mod.ts$78-95.ts:3:5

TS2304 [ERROR]: Cannot find name 'logger'.
    logger().debug(`running ${a} * ${b}`);
    ~~~~~~
    at file:///Users/asher/GitHub/std/log/mod.ts$78-95.ts:7:5

These same snippets run fine:

import { getLogger } from "@std/log";

const logger = getLogger("my-awesome-module");

export function sum(a: number, b: number) {
  logger.debug(`running ${a} + ${b}`); // no message will be logged, because getLogger() was called before log.setup()
  return a + b;
}

import { getLogger } from "@std/log";

function logger() {
  return getLogger("my-awesome-module");
}

export function sum(a: number, b: number) {
  logger().debug(`running ${a} + ${b}`);
  return a + b;
}

export function mult(a: number, b: number) {
  logger().debug(`running ${a} * ${b}`);
  return a * b;
}

Version: Deno 2.0.0-rc.3+c3bc692

[magurotuna]

Here's why this issue happens - this code snippet

import { getLogger } from "@std/log";

const logger = getLogger("my-awesome-module");

export function sum(a: number, b: number) {
  logger.debug(`running ${a} + ${b}`); // no message will be logged, because getLogger() was called before log.setup()
  return a + b;
}

is first virtually converted into

import { getLogger } from "@std/log";

Deno.test("<test-name>", async () => {
  const logger = getLogger("my-awesome-module");

  export function sum(a: number, b: number) {
    logger.debug(`running ${a} + ${b}`); // no message will be logged, because getLogger() was called before log.setup()
    return a + b;
  }
});

but right after this, the code converter (precisely speaking, swc) detects that export function is not on the top level scope, which violates the spec. So this ends up being turned into:

import { getLogger } from "@std/log";

Deno.test("<test-name>", async () => {
  const logger = getLogger("my-awesome-module");
});

export function sum(a: number, b: number) {
  logger.debug(`running ${a} + ${b}`); // no message will be logged, because getLogger() was called before log.setup()
  return a + b;
}

Therefore logger unintentionally becomes an undeclared variable in the body of sum function.

I'll try to consider what would be the best fix for this.

[iuioiua]

I suggest printing a warning for a snippet containing exported symbols. I don't think snippets would typically contain them. In the meantime, I'll remove the export keywords from std.

[magurotuna]

That sounds like a sensible solution, though I had started with the difference approach which can be seen #2570. The idea is to remove export to allow items annotated with export can be put inside Deno.test scope. What do you think about this approach?