JDK-8300691 - final variables in for loop headers should accept updates

[Maurizio Cimadamore]

Hi Archie,
looks very good. Only one comment. Here:

|// Check for a possible "dummy variable" declaration if (tree.sym.pos 
 >= startPos && (tree.sym.owner.kind == MTH || tree.sym.owner.kind == 
VAR) && tree.init instanceof JCIdent) dummyVariables.put(tree.sym, new 
DummyVariable(tree.pos(), tree.sym)); |

I think we have to check whether the symbol under tree.init is that of a 
local variable. E.g. we don’t want the finder to pick up stuff like:

|String a = b |

Where |b| is a field in the current class.

Maurizio

On 16/10/2024 21:44, Archie Cobbs wrote:

> Hi Maurizio,
>
> Please see 
> https://github.com/openjdk/jdk/compare/master...archiecobbs:jdk:dummy-variable-detector?expand=1 
> <https://urldefense.com/v3/__https://github.com/openjdk/jdk/compare/master...archiecobbs:jdk:dummy-variable-detector?expand=1__;!!ACWV5N9M2RV99hQ!PvoKchzkcMwwmqdsV9XWt5JA-wk3qU-XscUSdoueEGvgGTk7vKFqEU1JV0jYo3wMu-GvkpqF9U3pblph5Zn2BnccfYMOdQ$>
>
> I made it a note instead of a warning so that builds would not be 
> artificially halted.
>
> Here's an example:
>
> $ cat Test.java
> class Test {
>     {
>         for (int i = 1; i <= 3; i++) {
>             int i2 = i;
>             Runnable r = () -> System.out.println(i2);
>         }
>     }
> }
> $ javac Test.java
> flex-test/Test.java:4: Note: detected effectively final "dummy 
> variable" i2
>             int i2 = i;
>                 ^
> I *think* the logic is accurate but it could probably use a quick review.
>
> -Archie
>
> On Wed, Oct 16, 2024 at 9:11 AM Archie Cobbs <archie.cobbs at gmail.com> 
> wrote:
>
>     Hi Maurizio,
>
>     On Wed, Oct 16, 2024 at 8:56 AM Maurizio Cimadamore
>     <maurizio.cimadamore at oracle.com> wrote:
>
>         Could you come up with a javac patch that detects such “dummy”
>         variable declarations and prints a note/warning in the
>         compiler output?
>
>     Excellent idea - I agree this is something worth further
>     exploration to better understand.
>
>     I will work on it and report back.
>
>     -Archie
>
>     -- 
>     Archie L. Cobbs
>
>
>
> -- 
> Archie L. Cobbs

​
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