If a program (say, ninja) tries to be compatible with gnu make's depfile 
parsing, it would previously convert "\ " to a space from what I understand. 
Now it's going to get "\\\ " and think that that's "\ ".

You're mixing things up.  #include "\ " would be converted by gcc to "\\ " 
(because it escapes the space but not the backslash) which would be de-escaped 
by GNU Make as "\" followed by a space delimiter.
Now Clang will give it "\\\ " which will be handled as "\ " which is correct.
(Remember that the string you hand to #include is NOT a normal C string; it has 
no escaping in it.)
--paulr

From: [email protected] [mailto:[email protected]] 
On Behalf Of Nico Weber
Sent: Friday, May 08, 2015 4:36 PM
To: [email protected]
Cc: [email protected]
Subject: Re: [PATCH] Fix dependency file escaping

On Fri, May 8, 2015 at 4:01 PM, Paul Robinson 
<[email protected]<mailto:[email protected]>> 
wrote:
In http://reviews.llvm.org/D9208#169446, @thakis wrote:

> Does gcc intend to fix this soon? Isn't being compatible with gcc important
>  than the other things?


If gcc emitted an incorrect relocation, would you argue that it's important to 
be compatible with gcc?  Even if you could not point to any linker that handled 
that buggy relocation in a reasonable way?

'course not, but that's not the case here. If a program (say, ninja) tries to 
be compatible with gnu make's depfile parsing, it would previously convert "\ " 
to a space from what I understand. Now it's going to get "\\\ " and think that 
that's "\ ". So this is breaking backwards compat of clang with itself.
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