[jcperez-ch]

Summary:
Replaces three sketchy-null suppressions in Metro with explicit checks that keep the exact runtime behavior.

• metro-transform-plugins/src/constant-folding-plugin.js: removes $FlowFixMe[sketchy-null-mixed] on path.replaceWith(result.value ? node.consequent : node.alternate). result.value is unknown, so the test becomes Boolean(result.value). That is the same truthiness test the ternary did implicitly, for every value. It is read into const valueIsTruthy first because Metro's ESLint no-extra-boolean-cast flags Boolean() directly in a ternary test. The existing $FlowFixMe[incompatible-type] on the call is unchanged.
• metro/src/DeltaBundler/Serializers/getRamBundleInfo.js: removes $FlowFixMe[sketchy-null-bool] on preloadedModules || {}. preloadedModules is typed ?Readonly<{[path: string]: true}> | false. An object is always truthy, so || falls back exactly for null, undefined and false; the new check is preloadedModules != null && preloadedModules !== false ? preloadedModules : {}.
• metro-symbolicate/src/symbolicate.js (readAll): removes // flowlint-next-line sketchy-null-string:off on while ((chunk = stream.read())). read() returns ?(string | Buffer); a Buffer is always truthy, so the loop stopped exactly on null, undefined or ''. The loop now reads before the check and again at the end of the body, with while (chunk != null && chunk !== ''). read() is still called once per iteration and the loop stops on the same values. The read is split out because Flow does not refine a value assigned inside a loop condition.

No || was rewritten to ??. No new suppressions, casts, any, comments, or tests. metro-symbolicate has no checked-in symbolicate.js.flow; the .js.flow copies only exist under node_modules and are generated by the build.

Changelog: [Internal]

Differential Revision: D127164728

[meta-codesync]

@jcperez-ch has exported this pull request. If you are a Meta employee, you can view the originating Diff in D127164728.