RFR: 8329951: `var` emits deprecation warnings that do not point to the file or position [v4]

[Archie Cobbs]

On Mon, 2 Jun 2025 23:46:11 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

>> This PR fixes a bug that causes certain warnings to be emitted without source file location information.
>> 
>> Consider this example:
>> 
>> import java.util.*;
>> import java.util.function.*;
>> public class Example {
>> 
>>     @SuppressWarnings("deprecation")
>>     List<Observable> m1() { return null; }
>> 
>>     void m2() {
>>         for (var o : m1()) { }
>>     }
>> }
>> 
>> the compiler outputs this:
>> 
>> $ javac -Xlint:deprecation Example.java 
>> warning: [deprecation] Observable in java.util has been deprecated
>> 1 warning
>> 
>> but it should instead output this:
>> 
>> Example.java:9: warning: [deprecation] Observable in java.util has been deprecated
>>         for (var o : m1()) { }
>>              ^
>> 1 warning
>> 
>> The bug happens because the "synthetic" type that is installed dynamically for implicitly typed variables is not given a source code position. This makes some sense (?) because that type doesn't literally appear in the variable declaration; however, certain error messages expect to be able to point to the type portion of a variable declaration, so it also causes this bug (and presumably similar variants). To fix this, we just copy the position of the variable declaration itself to the synthetic type.
>> 
>> However, this change necessitated another change: The fix for [JDK-8200199](https://bugs.openjdk.org/browse/JDK-8200199) added back in 2018 relies on the fact that the position of an implicitly typed variable is always null, so this change breaks that fix. But since then, a new method `JCVariableDecl.declaredUsingVar()` was added, so we can just use that test instead. This also makes the code a little clearer.
>
> Archie Cobbs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove now-useless method RedundantLocalVarTypeAnalyzerBase.isImplicitlyTyped().

Thanks for the review!

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PR Comment: https://git.openjdk.org/jdk/pull/23683#issuecomment-2933163167