Empty macro expansion from inside another macro causes incorrect placement of expanded macro

[llvmbot]

Bugzilla Link	18485
Version	unspecified
OS	Windows NT
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

Empty macro expansion from inside another macro causes incorrect placement of expanded macro.
Consider the example:

#define B

#define A(type) B unsigned type
/*
empty lines
...
...
...
...*/
A(int) foo()
{}

The clang preprocessor (-E option) will output the following:

#line 1 "D:/home/paul/sample.c"
#line 1 "<built-in>"
#line 1 "<built-in>"
#line 156 "<built-in>"
#line 1 "<command line>"
#line 1 "<built-in>"
#line 1 "D:/home/paul/sample.c" unsigned int
#line 10 "D:/home/paul/sample.c"
       foo()
{}

Take a note, that the return type of the foo function is placed before #line 10, meaning that it is placed before the whitespace, thus incorrectly pointing the start position of the foo to line 1 instead of line 10.

[AaronBallman]

This issue was fixed in Clang 3.5: https://godbolt.org/z/v38EdT9oE

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (llvmbot)

Details

| | | | --- | --- | | Bugzilla Link | [18485](https://llvm.org/bz18485) | | Version | unspecified | | OS | Windows NT | | Reporter | LLVM Bugzilla Contributor | | CC | @DougGregor |

Extended Description

Empty macro expansion from inside another macro causes incorrect placement of expanded macro.
Consider the example:

#define B

#define A(type) B unsigned type
/*
empty lines
...
...
...
...*/
A(int) foo()
{}

The clang preprocessor (-E option) will output the following:

#line 1 "D:/home/paul/sample.c"
#line 1 "<built-in>"
#line 1 "<built-in>"
#line 156 "<built-in>"
#line 1 "<command line>"
#line 1 "<built-in>"
#line 1 "D:/home/paul/sample.c" unsigned int
#line 10 "D:/home/paul/sample.c"
       foo()
{}

Take a note, that the return type of the foo function is placed before #line 10, meaning that it is placed before the whitespace, thus incorrectly pointing the start position of the foo to line 1 instead of line 10.