Snapshots are different on linux and windows when contain `\\`

[alexander-akait]

🐛 Bug Report

Snapshoting RegExp on windows and linux are difference when it is contains \\.

To Reproduce

describe("regexp", () => {
	it("should work", () => {
		expect({ test: /[\\/]node_modules[\\/]/ }).toMatchInlineSnapshot();
	});
});

Expected behavior

Snapshots should escaped property and equally on windows and linux

Link to repl or repo (highly encouraged)

Original issue: webpack/webpack#10443

envinfo

npx: installed 1 in 2.375s

  System:
    OS: Linux 5.3 Ubuntu 19.10 (Eoan Ermine)
    CPU: (6) x64 AMD FX(tm)-6300 Six-Core Processor
  Binaries:
    Node: 10.15.2 - /usr/bin/node
    Yarn: 1.13.0 - /usr/bin/yarn
    npm: 6.13.7 - /usr/local/bin/npm
  npmPackages:
    jest: ^25.1.0 => 25.1.0 

Additional information: there were no problems using jest@24, looks like it is a regression

[SimenB]

@pedrottimark ideas?

[SimenB]

The regexp part of pretty-format hasn't changed for years

https://github.com/facebook/jest/blob/003bd50afaf0022381ffa9eb30abd511fad2ed2e/packages/pretty-format/src/index.ts#L157-L163

So I'm not sure where to begin looking into this... Maybe the equality function just lies? It was tweaked in #9167. RegExp equality went from

    return (
        a.source == b.source &&
        a.global == b.global &&
        a.multiline == b.multiline &&
        a.ignoreCase == b.ignoreCase
      );

to

return a.source === b.source && a.flags === b.flags;

I wouldn't expect that to result in this change, though...
@jeysal ideas?

[alexander-akait]

@SimenB I can spent my time on searching a problem, I'm afraid that it will take me more time for me, so I created the problem, suddenly there are some known potential problem areas

[jeysal]

Hmm I'd be surprised if it was related to that too. It should only matter for flags other than those 3

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