r200787 - Fix whitespace handling in empty macro expansions

[Harald van Dijk]

On 05/02/14 00:42, Richard Smith wrote:
> Here's an easy test:
> 
> #define foo() bar() b
> #define bar()
> a
> foo()
> c
> 
> This should produce:
> 
> # 1 "..."
> 
> 
> a
>  b
> c
> 
> ... but currently produces:
> 
> #1 "..."
> 
> 
> a b
> 
> c

Thanks Richard, I don't know how I managed to miss that.

Setting Token::StartOfLine as mentioned gets this right in the lexer.
However, even though the b token in the output has both
Token::StartOfLine and Token::LeadingSpace set,
PrintPPOutputPPCallbacks::HandleFirstTokOnLine uses the column number to
determine whether to print spaces, not the flag. As a result, the output
becomes not

a
 b
c

but

a
b
c

Given that the lexer behaviour is now right, would it be okay to leave
this as it is, and only add a test to check that b is on a separate
line, like attached? (I used first/second/third instead of a/b/c in an
attempt to get FileCheck to print a better suggestion when the test
fails, but it neither helps nor hurts.)

Cheers,
Harald van Dijk
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