Question

I’m trying out Google Closure, specifically the annotating stuff to enforce type safety. To test I did something wrong, though the compiler won’t tell me that it is…

Here’s the code:

// ==ClosureCompiler==
// @output_file_name default.js
// @compilation_level SIMPLE_OPTIMIZATIONS
// ==/ClosureCompiler==

/**
 * A card.
 * @constructor
 * @param {String} cardName The exact name of the card
 * @param {Kinetic.Layer} layer The layer for the card
 */
function CardObject(cardName, layer)
{
    /** @type {Number} */
    var number = cardName;
}

So, I have a variable number which I say is a Number, and I try to assign a string to it. This shouldn’t be possible, right? Though the compiler won’t tell me that…

Why won’t it tell me that’s wrong?

Answer 1

Closure Compiler uses warning levels to determine which checks are enabled during the compilation process. The three warning levels are:

• QUIET
• DEFAULT
• VERBOSE

For example, using compilation level SIMPLE_OPTIMIZATIONS, you will still get type-check warnings with the warning level set to VERBOSE.

// ==ClosureCompiler==
// @output_file_name default.js
// @compilation_level SIMPLE_OPTIMIZATIONS
// @warning_level VERBOSE
// ==/ClosureCompiler==

/**
 * A card.
 * @constructor
 * @param {String} cardName The exact name of the card
 * @param {Kinetic.Layer} layer The layer for the card
 */
function CardObject(cardName, layer)
{
    /** @type {Number} */
    var number = cardName;
}

Output

Number of warnings: 2

JSC_TYPE_PARSE_ERROR: Bad type annotation. Unknown type Kinetic.Layer at line 5
character 10  
* @param {Kinetic.Layer} layer The layer for the card
          ^
JSC_TYPE_MISMATCH: initializing variable
found   : (String|null|undefined)
required: (Number|null) at line 10 character 13
var number = cardName;
             ^

To understand exactly which checks are associated with each warning level, here is the relevant code from WarningLevels.java.

QUIET

/**
 * Silence all non-essential warnings.
 */
private static void silenceAllWarnings(CompilerOptions options) {
  // Just use a ShowByPath warnings guard, so that we don't have
  // to maintain a separate class of warnings guards for silencing warnings.
  options.addWarningsGuard(
      new ShowByPathWarningsGuard(
          "the_longest_path_that_cannot_be_expressed_as_a_string"));

  // Allow passes that aren't going to report anything to be skipped.

  options.checkRequires = CheckLevel.OFF;
  options.checkProvides = CheckLevel.OFF;
  options.checkMissingGetCssNameLevel = CheckLevel.OFF;
  options.aggressiveVarCheck = CheckLevel.OFF;
  options.checkTypes = false;
  options.setWarningLevel(DiagnosticGroups.CHECK_TYPES, CheckLevel.OFF);
  options.checkUnreachableCode = CheckLevel.OFF;
  options.checkMissingReturn = CheckLevel.OFF;
  options.setWarningLevel(DiagnosticGroups.ACCESS_CONTROLS, CheckLevel.OFF);
  options.setWarningLevel(DiagnosticGroups.CONST, CheckLevel.OFF);
  options.setWarningLevel(DiagnosticGroups.CONSTANT_PROPERTY, CheckLevel.OFF);
  options.checkGlobalNamesLevel = CheckLevel.OFF;
  options.checkSuspiciousCode = false;
  options.checkGlobalThisLevel = CheckLevel.OFF;
  options.setWarningLevel(DiagnosticGroups.GLOBAL_THIS, CheckLevel.OFF);
  options.setWarningLevel(DiagnosticGroups.ES5_STRICT, CheckLevel.OFF);
  options.checkCaja = false;
}

DEFAULT

/**
 * Add the default checking pass to the compilation options.
 * @param options The CompilerOptions object to set the options on.
 */
private static void addDefaultWarnings(CompilerOptions options) {
  options.checkSuspiciousCode = true;
  options.checkUnreachableCode = CheckLevel.WARNING;
  options.checkControlStructures = true;
}

VERBOSE

/**
 * Add all the check pass that are possibly relevant to a non-googler.
 * @param options The CompilerOptions object to set the options on.
 */
private static void addVerboseWarnings(CompilerOptions options) {
  addDefaultWarnings(options);

  // checkSuspiciousCode needs to be enabled for CheckGlobalThis to get run.
  options.checkSuspiciousCode = true;
  options.checkGlobalThisLevel = CheckLevel.WARNING;
  options.checkSymbols = true;
  options.checkMissingReturn = CheckLevel.WARNING;

  // checkTypes has the side-effect of asserting that the
  // correct number of arguments are passed to a function.
  // Because the CodingConvention used with the web service does not provide a
  // way for optional arguments to be specified, these warnings may result in
  // false positives.
  options.checkTypes = true;
  options.checkGlobalNamesLevel = CheckLevel.WARNING;
  options.aggressiveVarCheck = CheckLevel.WARNING;
  options.setWarningLevel(
      DiagnosticGroups.MISSING_PROPERTIES, CheckLevel.WARNING);
  options.setWarningLevel(
      DiagnosticGroups.DEPRECATED, CheckLevel.WARNING);
}

Notice that options.checkTypes = true; is only set for the VERBOSE warning level. As Speransky Danil pointed out, type checking is also enabled when using compilation level ADVANCED_OPTIMIZATIONS.

In addition, classes of warnings may be controlled individually with the Closure Compiler application (jar file) using compiler flags:

• –jscomp_off
• –jscomp_warning
• –jscomp_error

The warning classes that may be specified are as follows:

• accessControls
• ambiguousFunctionDecl
• checkRegExp
• checkTypes
• checkVars
• const
• constantProperty
• deprecated
• duplicateMessage
• es5Strict
• externsValidation
• fileoverviewTags
• globalThis
• internetExplorerChecks
• invalidCasts
• missingProperties
• nonStandardJsDocs
• strictModuleDepCheck
• typeInvalidation
• undefinedNames
• undefinedVars
• unknownDefines
• uselessCode
• visibility

For example, type checking warnings could be enabled individually:

--jscomp_warning=checkTypes