JDK 10/11 RFR of JDK-8189146: Have use of "var" in 9 and earlier source versions issue a warning

[joe darcy]

Hi Maurizio,


On 1/9/2018 10:49 AM, Maurizio Cimadamore wrote:
> Hi Joe,
> I'm a bit unsure about having a retroactive warning in JDK 10 - e.g. 
> I'm not sure how useful that would be, but I get the spirit of what 
> you're getting at.

I think this kind of warning allows a smoother cross-release transition.

>
> In terms of code, I think your warning should go inside the 
> isRestrictedLocalVarTypeName(Name), which is called in a few places 
> (not just the one you have touched). For instance, I don't think your 
> patch will cover this case:
>
> List<var> l = null;
>
> So, the code for isRestrictedLocalVarTypeName(Name) is currently:
>
> return allowLocalVariableTypeInference && name == names.var;
>
> I think it should be updated to:
>
> if (name == names.var) {
>             if (allowLocalVariableTypeInference) {
>                 return true;
>             } else {
>                 warning(pos, "var.not.allowed", name);
>             }
>         }
>         return false;
>
>
> Of course you need to enhance the method to take an extra position 
> argument (pos).
>
>

Webrev updated as suggested:

     http://cr.openjdk.java.net/~darcy/8189146.1/

That does emit more warnings than the earlier iteration in ParserTest, 
17 rather than 6. As a review aid, the 17 expanded non-raw warnings are 
listed below. Under release 10, there are 24 errors generated for the 
file, including different error messages.

Thanks,

-Joe

/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:14: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
class ParserTest<var> {
                  ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:16: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         static class var { } //illegal
                      ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:20: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         interface var { } //illegal
                   ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:24: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         enum var { } //illegal
              ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:28: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         @interface var { } //illegal
                    ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:36: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
     static class var extends RuntimeException { } //illegal
                  ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:38: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
     var x = null; //illegal
     ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:54: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
     var m() { //illegal
     ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:58: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
     void test2(var x) { //error
                ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:59: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         List<var> l1; //error
              ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:60: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         List<? extends var> l2; //error
                        ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:61: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         List<? super var> l3; //error
                      ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:63: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
             Function<var, String> f = (var x2) -> ""; //error
                      ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:63: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
             Function<var, String> f = (var x2) -> ""; //error
                                        ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:64: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         } catch (var ex) { } //error
                  ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:68: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         boolean b1 = o instanceof var; //error
                                   ^
/home/darcy/JDK/10/hg/test/langtools/tools/javac/lvti/ParserTest.java:69: 
warning: as of release 10, 'var' is a restricted local variable type and 
cannot be used for type declarations
         Object o2 = (var)o; //error
                      ^
17 warnings