[react-devtools] Fix trailing percent sign in formatConsoleArguments …

Summary

formatConsoleArguments (used by the DevTools backend to inline console substitutions) walks the format string and inlines %s/%d/%i/%f arguments while leaving %c/%o/%O in place. For each % it reads the next character to decide what to do.

When the format string ends with a lone % - e.g. console.log('Progress 100%', value) - the character after % is undefined, and the default branch ran:

template += `%${nextChar}`; // -> "%undefined"

So the function emitted the literal text %undefined:

formatConsoleArguments('Progress 100%', 'extra');
// before: ['Progress 100%undefined', 'extra']
// after: ['Progress 100%', 'extra']

Browsers render a trailing % in a console format string as a literal percent sign, so this PR keeps it as % when there is no following character.

How did you test this change?

Added a keeps a trailing percent sign test to the existing formatConsoleArguments suite in utils-test.js (covering both a bare trailing % and one that follows another substitution). Since the function is pure and import-free, I also verified the patched logic against every existing case in that suite plus the new ones to confirm there are no regressions.

Commit 53b5c3c authored

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