Re: [PATCH v3 1/3] userdiff: support Java type parameters

[Andrei Rybak <rybak.a.v@gmail.com>]

On 2023-02-08T00:42, Andrei Rybak wrote:
> A class or interface in Java can have type parameters following the name
> in the declared type, surrounded by angle brackets (paired less than and
> greater than signs).[2]   The type parameters -- `A` and `B` in the
> examples -- may follow the class name immediately:
> 
>      public class ParameterizedClass<A, B> {
>      }
> 
> or may be separated by whitespace:
> 
>      public class SpaceBeforeTypeParameters <A, B> {
>      }
> 
> A part of the builtin userdiff pattern for Java matches declarations of
> classes, enums, and interfaces.  The regular expression requires at
> least one whitespace character after the name of the declared type.
> This disallows matching for opening angle bracket of type parameters
> immediately after the name of the type.  Mandatory whitespace after the
> name of the type also disallows using the pattern in repositories with a
> fairly common code style that puts braces for the body of a class on
> separate lines:
> 
>      class WithLineBreakBeforeOpeningBrace
>      {
>      }
> 
> Support matching Java code in more diverse code styles and declarations
> of classes and interfaces with type parameters immediately following the
> name of the type in the builtin userdiff pattern for Java.  Do so by
> just matching anything until the end of the line after the keywords for
> the kind of type being declared.

The above explains why removing the mandatory matching for whitespace
after the class name is needed, but it doesn't explain why removing
the part of the regex that matches the class name itself is OK.
Perhaps, something like this could be added:

     An possible approach could be to keep matching the name of the
     type: "...[ \t]+[A-Za-z][A-Za-z0-9_$]*.*)$\n", but without matching
     mandatory whitespace after the name of the type, matching the name
     itself separately isn't useful for our purposes.

?

> [1] Since Java 5 released in 2004.
> [2] Detailed description is available in the Java Language
>      Specification, sections "Type Variables" and "Parameterized Types":
>      https://docs.oracle.com/javase/specs/jls/se17/html/jls-4.html#jls-4.4
> 
> Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
> ---

[...]

> diff --git a/userdiff.c b/userdiff.c
> index d71b82feb7..bc5f3ed4c3 100644
> --- a/userdiff.c
> +++ b/userdiff.c
> @@ -171,7 +171,7 @@ PATTERNS("html",
>   PATTERNS("java",
>   	 "!^[ \t]*(catch|do|for|if|instanceof|new|return|switch|throw|while)\n"
>   	 /* Class, enum, and interface declarations */
> -	 "^[ \t]*(([a-z]+[ \t]+)*(class|enum|interface)[ \t]+[A-Za-z][A-Za-z0-9_$]*[ \t]+.*)$\n"
> +	 "^[ \t]*(([a-z]+[ \t]+)*(class|enum|interface)[ \t]+.*)$\n"
>   	 /* Method definitions; note that constructor signatures are not */
>   	 /* matched because they are indistinguishable from method calls. */
>   	 "^[ \t]*(([A-Za-z_<>&][][?&<>.,A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$",