Emit warning for identifiers starting with __

[dlangBugzillaToGithub]

dayllenger reported this on 2018-06-26T08:31:41Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19028

CC List

• Steven Schveighoffer (@schveiguy)

Description

Identifiers starting with `__` are reserved for compiler and their behaviour is implementation-defined. But compilers do not show warning or error message when you try to use such names. Furthermore, some functions ignore these identifiers and may produce hidden bugs in a code. For example:

void main()
{
    writeln([__traits(allMembers, S)]); // will print only ["a"]
}

struct S
{
    int a;
    int __refCount;
}

Documentation of `allMembers` says nothing about this behaviour.

Links:
https://dlang.org/spec/lex.html#identifiers
https://dlang.org/spec/traits.html#allMembers
https://github.com/dlang/dmd/blob/2ce74fc1180a3b0ed5e5c29aa79bf3773af5d5b7/src/dmd/traits.d#L1385
https://forum.dlang.org/thread/yauflbmphapnnksckksu@forum.dlang.org

[dlangBugzillaToGithub]

schveiguy (@schveiguy) commented on 2018-06-26T14:35:39Z

My suggestion is to only emit warnings for packages that are not owned by the language. In other words, the language should be free to add these types of symbols in std.*, rt.*, core.*, and object without complaint.