Integrated: 8268312: Compilation error with nested generic functional interface

[Vicente Romero]

On Mon, 20 Sep 2021 19:00:29 GMT, Vicente Romero <vromero at openjdk.org> wrote:

> Please review this PR, which is my proposal to fix an existing regression. This code:
> 
> 
> import java.util.Optional;
> 
> class App {
>     public static void main(String[] args) {
>         Optional.of("").map(outer -> {
>             Optional.of("")
>                 .map(inner -> returnGeneric(outer))
>                 .ifPresent(String::toString);
>             return "";
>         });
>     }
> 
>     private static <RG> RG returnGeneric(RG generic) {
>         return generic;
>     }
> }
> 
> is not accepted by javac but if the user passes the `-Xdiags:verbose` option then the code compiles. I tracked down the reason for this puzzling difference and I found that it is due to our diagnostic rewriters which can generate more detailed positions for error messages but in cases like the one above can trick the compiler to generate an error message too early. The code deciding if an error message should be deferred or not, depending on the position, is at `DeferredDiagnosticHandler::report`. We decide to do the rewriting if we are in diagnostics compact mode, this is why the error doesn't occur with the `-Xdiags:verbose` option. This fix will made some diagnostics to appear at a slightly different position, but won't make the compiler reject correct code. Comments?
> 
> TIA

This pull request has now been integrated.

Changeset: f3abb829
Author:    Vicente Romero <vromero at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/f3abb82989e79da97bcc0a837883be41d14703a3
Stats:     120 lines in 5 files changed: 109 ins; 8 del; 3 mod

8268312: Compilation error with nested generic functional interface

Reviewed-by: mcimadamore

-------------

PR: https://git.openjdk.org/jdk/pull/5586