Fix custom syntax require error handling

[ybiquitous]

Which issue, if any, is this issue related to?

• See Fix custom syntax module path not properly resolving #5632
• See Cannot resolve custom syntax module "postcss-scss" stylelint-scss/stylelint-config-standard-scss#2

Is there anything in the PR that needs further explanation?

Node.js require() may cause other errors than MODULE_NOT_FOUND. This change aims to throw such errors.
See also: https://nodejs.org/api/errors.html#errors_module_not_found

[jeddy3]

LGTM, thanks!

[jeddy3]

• Fixed: custom syntax require error handling (#5635).

[XhmikosR]

Just wondering, couldn't we start using the optional chaining operator in cases like this? Like error?.code === 'MODULE_NOT_FOUND'

[jeddy3]

I don't think optional chaining is available in node 12.20. (see node green and mdn). If it is, though, we can adopt it.

[XhmikosR]

Ah, true, I guess one thing to do when Node.js 12 support is dropped :)

[cschwebk]

@jeddy3 A possible improvement to this error message would be to include the full error message and require stack in the output, instead of assuming that the module that cannot be found is the value in customSyntax. I ran into this same error message today due to an unfulfilled peerDependency (postcss-syntax is a peerDependency of @stylelint/postcss-css-in-js).

$ stylelint src/client/**/*.{js,scss}
Error: Cannot find module 'postcss-syntax/load-syntax'
Require stack:
- /Users/cschwebk/project/node_modules/@stylelint/postcss-css-in-js/extract.js
- /Users/cschwebk/project/node_modules/@stylelint/postcss-css-in-js/index.js
- /Users/cschwebk/project/stylelint.config.js
- /Users/cschwebk/project/node_modules/stylelint/node_modules/cosmiconfig/dist/loaders.js
- /Users/cschwebk/project/node_modules/stylelint/node_modules/cosmiconfig/dist/ExplorerBase.js
- /Users/cschwebk/project/node_modules/stylelint/node_modules/cosmiconfig/dist/Explorer.js
- /Users/cschwebk/project/node_modules/stylelint/node_modules/cosmiconfig/dist/index.js
- /Users/cschwebk/project/node_modules/stylelint/lib/getConfigForFile.js
- /Users/cschwebk/project/node_modules/stylelint/lib/createStylelint.js
- /Users/cschwebk/project/node_modules/stylelint/lib/printConfig.js
- /Users/cschwebk/project/node_modules/stylelint/lib/cli.js
- /Users/cschwebk/project/node_modules/stylelint/bin/stylelint.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:889:15)
    at Function.Module._load (internal/modules/cjs/loader.js:745:27)
    at Module.require (internal/modules/cjs/loader.js:961:19)
    at require (/Users/cschwebk/project/node_modules/v8-compile-cache/v8-compile-cache.js:159:20)
    at Object.<anonymous> (/Users/cschwebk/project/node_modules/@stylelint/postcss-css-in-js/extract.js:4:20)
    at Module._compile (/Users/cschwebk/project/node_modules/v8-compile-cache/v8-compile-cache.js:192:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1101:10)
    at Module.load (internal/modules/cjs/loader.js:937:32)
    at Function.Module._load (internal/modules/cjs/loader.js:778:12)
    at Module.require (internal/modules/cjs/loader.js:961:19)

[jeddy3]

improvement to this error message would be to include the full error message and require stack in the output, instead of assuming that the module that cannot be found is the value in customSyntax.

Sounds good. Pull request welcome.