RFR: 8027682: javac wrongly accepts semicolons in package and import decls [v5]

[Vicente Romero]

On Fri, 10 Feb 2023 15:16:19 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 semicolon is a valid _TopLevelClassOrInterfaceDeclaration_, it is not a valid _ImportDeclaration_. Therefore, if we see a lone semicolon 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 semicolon.
>> 
>> 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 semicolon.
>> * 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
>
> Archie L. Cobbs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Generate warnings instead of errors for source levels < 21.
>   
>   This improves backward compatibility as requested in the CSR (JDK-8301905).

test/langtools/tools/javac/diags/examples/ExtraneousSemiColonError.java line 29:

> 27: import java.util.Set;
> 28: 
> 29: class ExtraneousSemiColonError {

I think that we should have a dedicated test for the new feature, apart from the diagnostics oriented ones. The test could be executed twice once with option `-source 20` and once without it and provided two golden files accordingly.

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