Add support for extern variable declarations

[jonas]

The following declarations are not currently supported.

extern int forty_two;
extern enum { SYSTEM, USER } who;
extern const char version[];
extern struct {
    int major;
    int minor;
    int patch;
} semver;

AST

> clang -Xclang -ast-dump -fsyntax-only tests/samples/Extern.h
TranslationUnitDecl 0x7fcd6b004ae8 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x7fcd6b005060 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'
| `-BuiltinType 0x7fcd6b004d80 '__int128'
|-TypedefDecl 0x7fcd6b0050d0 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'
| `-BuiltinType 0x7fcd6b004da0 'unsigned __int128'
|-TypedefDecl 0x7fcd6b0053a8 <<invalid sloc>> <invalid sloc> implicit __NSConstantString 'struct __NSConstantString_tag'
| `-RecordType 0x7fcd6b0051b0 'struct __NSConstantString_tag'
|   `-Record 0x7fcd6b005128 '__NSConstantString_tag'
|-TypedefDecl 0x7fcd6b005440 <<invalid sloc>> <invalid sloc> implicit __builtin_ms_va_list 'char *'
| `-PointerType 0x7fcd6b005400 'char *'
|   `-BuiltinType 0x7fcd6b004b80 'char'
|-TypedefDecl 0x7fcd6b005708 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list 'struct __va_list_tag [1]'
| `-ConstantArrayType 0x7fcd6b0056b0 'struct __va_list_tag [1]' 1
|   `-RecordType 0x7fcd6b005520 'struct __va_list_tag'
|     `-Record 0x7fcd6b005498 '__va_list_tag'
|-VarDecl 0x7fcd6b005778 <tests/samples/Extern.h:1:1, col:12> col:12 forty_two 'int' extern
|-EnumDecl 0x7fcd6b849440 <line:2:8, col:28> col:8
| |-EnumConstantDecl 0x7fcd6b849500 <col:15> col:15 SYSTEM 'int'
| `-EnumConstantDecl 0x7fcd6b849548 <col:23> col:23 USER 'int'
|-VarDecl 0x7fcd6b8495e0 <col:1, col:30> col:30 who 'enum (anonymous enum at tests/samples/Extern.h:2:8)':'enum (anonymous at tests/samples/Extern.h:2:8)' extern
|-VarDecl 0x7fcd6b8496d8 <line:3:1, col:27> col:19 version 'const char []' extern
|-RecordDecl 0x7fcd6b849738 <line:4:8, line:8:1> line:4:8 struct definition
target
| |-FieldDecl 0x7fcd6b8497f8 <line:5:5, col:9> col:9 major 'int'
| |-FieldDecl 0x7fcd6b849858 <line:6:5, col:9> col:9 minor 'int'
| `-FieldDecl 0x7fcd6b8498b8 <line:7:5, col:9> col:9 patch 'int'
`-VarDecl 0x7fcd6b849950 <line:4:1, line:8:3> col:3 semver 'struct (anonymous struct at tests/samples/Extern.h:4:8)':'struct (anonymous at tests/samples/Extern.h:4:8)' extern

[kornilova203]

#62 has related code

[jonas]

OK, I will review it tomorrow.

[jonas]

I assume you mean it has related code for the IR representation?

[kornilova203]

#62 adds VisitVarDecl method that also should be used here
So it will be more convenient to wait until the pr is merged

[jonas]

Partially fixed in #80 with limitations due to scala-native/scala-native#202