-fms-compatibility: Clang should form a wide string literal from L#macro_arg in a function-like macro

[llvmbot]

Bugzilla Link	9984
Resolution	FIXED
Resolved on	Dec 14, 2014 22:19
Version	trunk
OS	All
Blocks	llvm/llvm-bugzilla-archive#13707
Reporter	LLVM Bugzilla Contributor
CC	@alexey-bataev,@majnemer,@DougGregor,@zmodem,@zygoloid,@rnk

Extended Description

the following code produces an error:

#define TESTL(x) L#x
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

The preprocessor appears to ignore the L inside the define as the literal declaring the string as a wide string. The code not using the macro passes without error.

Here is the analyzer output:

"Use of undeclared identifier 'L'"

This fails on both using the analyzer that ships with XCode 4.0.1 as well as svn trunk (test at revision 131851).

[DougGregor]

Clang is behaving correctly here (as does GCC). You can't both stringize a token and concatenate in one step. Instead, use:

#define TESTL2(x) L##x
#define TESTL(x) TESTL2(#x)
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

[llvmbot]

Clang is behaving correctly here (as does GCC). You can't both stringize a
token and concatenate in one step. Instead, use:

#define TESTL2(x) L##x
#define TESTL(x) TESTL2(#x)
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

It also works with:

#define TESTL(x) L###x
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

I wasn't sure of the desired behaviour of "L#x" in clang (or that GCC doesn't allow for it either), I ran into it while trying to analyze some Microsoft example code while working on a Visual Studio plugin for the clang analyzer. Is this something that should be added to the clang Microsoft extensions?

[rnk]

IMO we should consider lexing this as a single wide string literal in -fms-compatibility mode. There appear to be lots of Windows applications using this idiom to form wide string literals from macro arguments.

[alexey-bataev]

Fixed in revision 224228