What is the annotation to hide warning from unreachable code?

[juj]

It looks like the documentation page does not document the mechanism to mute a warning that stems from unreachable code?

I am getting

building:ERROR: C:/Users/jukkaj/AppData/Local/Temp/emscripten_temp_ey7njtln/hello_world.js:18416:51: WARNING - [JSC_UNREACHABLE_CODE] unreachable code
  18416|       if (GL.currentContext.version >= 2 && false) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.

where the unreachable code is intentional. I would like to annotate the whole function to not warn about this, but the doc page https://github.com/google/closure-compiler/wiki/Warnings does not have any mention about "unreachable".

Is this a case of documentation missing a spot, or is this feature missing?

[juj]

I see there is this in code:

https://github.com/google/closure-compiler/blob/43850b5db8bd10fcea312a174e469da6343110a4/src/com/google/javascript/jscomp/CheckUnreachableCode.java#L32C1-L34

  static final DiagnosticType UNREACHABLE_CODE = DiagnosticType.warning(
      "JSC_UNREACHABLE_CODE", "unreachable code");

and running node cli.js --help gives

Available Error Groups: accessControls, checkPrototypalTypes,
    checkRegExp, checkTypes, checkVars, conformanceViolations, const,
    constantProperty, deprecated, deprecatedAnnotations, duplicateMessage,
    es5Strict, externsValidation, functionParams, globalThis, invalidCasts,
    lintVarDeclarations, misplacedTypeAnnotation, missingOverride,
    missingPolyfill, missingProperties, missingProvide, missingRequire,
    missingReturn, missingSourcesWarnings, moduleLoad, moduleImport,
    msgDescriptions, nonStandardJsDocs, partialAlias, polymer,
    reportUnknownTypes, strictCheckTypes, strictMissingProperties,
    strictModuleDepCheck, strictPrimitiveOperators, suspiciousCode,
    typeInvalidation, undefinedVars, underscore, unknownDefines,
    unusedLocalVariables, unusedPrivateMembers, uselessCode,
    untranspilableFeatures,visibility

but I don't know how to translate that code JSC_UNREACHABLE_CODE into the correct error group? Maybe that is supposed to be uselessCode?

[lauraharker]

Yep, it's uselessCode.

You can look this up in https://github.com/google/closure-compiler/wiki/@suppress-annotations#error-to-suppression-map. I added a link from https://github.com/google/closure-compiler/wiki/Warnings#warnings-categories.

[juj]

Great, thanks! Btw, I wonder if it might make sense to directly print it in the warning/error that appears, like GCC and Clang do?

E.g. currently the warning prints WARNING - [JSC_UNREACHABLE_CODE] unreachable code.

Why not print WARNING - [uselessCode] unreachable code?

[juj]

Or alternatively, would it be possible to support @suppress{JSC_UNREACHABLE_CODE} in addition to @suppress{uselessCode}?

The two different warning code namespaces makes me confused, wondering why both need to exist, and why I as user need to know to map between the two. Would seem to be easier to just present and use one code namespace?

[lauraharker]

I agree it's confusing. We talked as a team earlier this year about both possibilities you've suggested but I don't see that we ever filed an issue to track it, so created #4114.