[FLEX-35329] Initializing member variable/constant that is [Deprecated] incorrectly throws extra warning

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Apache Flex 4.16.0
• Fix Version/s: Apache Flex 4.16.1
• Component/s: .Unspecified - Compiler
• Assignee: Josh Tynjala
• Reporter: Josh Tynjala
• Created: 22/Jun/17 17:18
• Updated: 25/Nov/17 19:06
• Resolved: 28/Jun/17 22:14

Description

Consider the following class:

Deprecated.as

package
{
	import flash.display.Sprite;

	public class Deprecated extends Sprite
	{
		[Deprecated]
		public static var STATIC_DEPRECATED:String = "static";

		[Deprecated]
		public static var STATIC_DEPRECATED2:String;

		[Deprecated]
		public var memberDeprecated:String = "member";

		[Deprecated]
		public var memberDeprecated2:String;

		public function Deprecated()
		{
			STATIC_DEPRECATED = "new value";
			Deprecated.STATIC_DEPRECATED = "new value";
			memberDeprecated = "new value";
			this.memberDeprecated = "new value";
			STATIC_DEPRECATED2 = "new value";
			Deprecated.STATIC_DEPRECATED2 = "new value";
			memberDeprecated2 = "new value";
			this.memberDeprecated2 = "new value";
		}
	}	
}

The compiler should give eight warnings for each of the lines in the constructor. However, it actually gives 10 warnings. Here are the two extra warnings:

/Users/joshtynjala/Desktop/Deprecated/src/Deprecated.as(8): col: 21 Warning: 'STATIC_DEPRECATED' has been deprecated.

		public static var STATIC_DEPRECATED:String = "static";
		                  ^

/Users/joshtynjala/Desktop/Deprecated/src/Deprecated.as(14): col: 14 Warning: 'memberDeprecated' has been deprecated.

		public var memberDeprecated:String = "member";
		           ^

Notice that there are no warnings for STATIC_DEPRECATED2 and memberDeprecated2 because they are not initialized. It's only when a member or static variable is initialized that the warnings are shown. It appears that when the compiler checks for usage of deprecated variables is a little too aggressive.

The Falcon compiler and Adobe's ASC 2.0 compiler do not give these same extra warnings. They only give a warning on actual usage.

These warnings make it difficult to deprecate a constant or another variable in an open source library. It makes compile-time noisy with a lot of warnings that need to be ignored.

Note: When compiling with a library in SWC form, the compiler does not show these warnings. I suspect that this is why this was never really encountered with the Flex framework, since the SWCs are pre-compiled. However, for many open source libraries, developers often simply use the source code with the -source-path compiler option instead of a pre-compiled SWC. That's when these warnings can be seen. As a long-time library developer, I never used [Deprecated] metadata because of this bug.

Solution, which I will implement:

In LintEvaluator, modify evaluate( Context cx, SetExpressionNode node ).

if (slot != null && !(node.expr instanceof QualifiedIdentifierNode))
{
	//if it's a qualified identifier node, then it's a member/static
	//variable on a class that is being initialized, like this:
	//public var memberVar:String = "hi";
	//this case should not have a warning!
	checkDeprecatedSlot(cx, node.expr, node.ref, slot);
}

The declaration of a member/static variable is a QualifiedIdentifierNode (qualified meaning that it may have modifiers like public/private, static, etc.), but actual usage will be an IdentifierNode instead. So, if it's a QualifiedIdentifierNode, we know that we don't need to check if the variable is deprecated or not.