define settings breaks require paths strings

[qnp]

Describe the bug

As some lib rely on global, I had to shim global with:

// vite.config.js
import { defineConfig } from 'vite'

export default defineConfig({
  define: {
    global: {},
  },
});

However, I have some JS files that are located in a directory named /global. The import import lib from @/my/global/lib.js is broken at build time when doing vite build:

Could not resolve './my/{}/lib' from src/main.js
error during build:
Error: Could not resolve './my/{}/lib' from src/main.js

which is not what is expected and could lead to lot of problems, because any defined variable can break any import string where the variable name is present. For instance, i have also some files called global-something.js, and they are transformed into {}-something.js...

Reproduction

break-global.zip
yarn && yarn build

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

  System:
    OS: macOS Mojave 10.14.6
    CPU: (8) x64 Intel(R) Core(TM) i7-8569U CPU @ 2.80GHz
    Memory: 136.35 MB / 16.00 GB
    Shell: 5.3 - /bin/zsh
  Binaries:
    Node: 12.20.1 - ~/.nvm/versions/node/v12.20.1/bin/node
    Yarn: 1.17.3 - ~/.yarn/bin/yarn
    npm: 6.14.10 - ~/.nvm/versions/node/v12.20.1/bin/npm
  Browsers:
    Chrome: 89.0.4389.114
    Firefox: 86.0.1
    Firefox Developer Edition: 71.0
    Firefox Nightly: 76.0a1
    Safari: 14.0.3
    Safari Technology Preview: 13.2
  npmPackages:
    vite: ^2.1.5 => 2.1.5

Used package manager: yarn

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[patak-dev]

The define docs were modified to better explain that it shouldn't be used to replace variables, but only constants here b4a1526 (still not deployed)
The replacements are done with a simple regex during build time, you should only use define for unique constants that are not going to interfere with the rest of the code when being replaced.