RFR: 8027682: javac wrongly accepts semicolons in package and import decls

[Liam Miller-Cushon]

On Mon, 6 Feb 2023 20:32:27 GMT, Archie L. Cobbs <duke at openjdk.org> wrote:

> JLS [§7.3](https://docs.oracle.com/javase/specs/jls/se19/html/jls-7.html#jls-7.3) specifies that while a lone semi-colon is a valid _TopLevelClassOrInterfaceDeclaration_, it is not a valid _ImportDeclaration_. Therefore, if we see a lone semi-colon while looking for the next import statement we have to advance and accept a class declaration, and we can therefore no longer accept any further `import` statements.
> 
> However, the compiler was allowing this, for example:
> 
> package p; import X; ;;; import Y; class Foo {}
> 
> The bug is that the parser was switching out of "look for imports" mode after parsing a valid class declaration, but it was not switching out of "look for imports" mode after parsing a lone semi-colon.
> 
> The fix to `JavacParser.java` is easy, however it also requires these adjustments to unit tests:
> 
> * Test `tree/T6963934.java` must go away, because it is verifying a bug that only happens when the above bogus input is successfully parsed, and this can no longer happen.
> * A bug in `lib/types/TypeHarness.java` was uncovered and fixed; it was inserting an extra semi-colon.
> * The following bugs, which check invalid syntax within import statements, now generate different parse errors and therefor needed their "golden output" updated:
>   * annotations/typeAnnotations/failures/AnnotatedImport.java
>   * annotations/typeAnnotations/failures/AnnotatedPackage1.java
>   * annotations/typeAnnotations/failures/AnnotatedPackage2.java

I would be happy to see this fixed, but note that there's going to be some compatibility impact from this to existing programs containing extra `;`, and it probably warrants a CSR.

There was some discussion in [the original compiler-dev thread](https://mail.openjdk.org/pipermail/compiler-dev/2013-August/006973.html) about whether the right fix was to change javac, or change the spec.

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PR: https://git.openjdk.org/jdk/pull/12448