[PATCH] Fix dependency file escaping

[Robinson, Paul]

Is this right? GCC and the current patch coincide on the handling of `\ `. The only deviation is in the `#` case, no?

Sorry, you are correct, GCC was getting "\ " right but "\#" wrong.  Clang was doing both wrong.
So, for Nico's example, "\ " would be converted to "\\\ " by gcc, but not by Clang, and that's being fixed by the patch.
But GCC would emit "\#" as "\\#" which GNU make would interpret as "\" followed by a comment, and if that failed, try to interpret it as "\\" followed by a comment, neither of which would look for the correct file.  The patch causes Clang to emit this as "\\\#" which lets GNU make find the right file.

Regarding ninja, I don't think ninja can directly read Make-style dependency files?  Its syntax naively looks different enough that I'm not really sure that's relevant here.
--paulr

From: Sean Silva [mailto:chisophugis at gmail.com]
Sent: Friday, May 08, 2015 6:40 PM
To: Robinson, Paul
Cc: Nico Weber; reviews+D9208+public+0ac91376ffbd3e34 at reviews.llvm.org; cfe-commits at cs.uiuc.edu
Subject: Re: [PATCH] Fix dependency file escaping



On Fri, May 8, 2015 at 5:57 PM, Robinson, Paul <Paul_Robinson at playstation.sony.com<mailto:Paul_Robinson at playstation.sony.com>> wrote:
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.

Is this right? GCC and the current patch coincide on the handling of `\ `. The only deviation is in the `#` case, no?

-- Sean Silva

(Remember that the string you hand to #include is NOT a normal C string; it has no escaping in it.)
--paulr

From: cfe-commits-bounces at cs.uiuc.edu<mailto:cfe-commits-bounces at cs.uiuc.edu> [mailto:cfe-commits-bounces at cs.uiuc.edu<mailto:cfe-commits-bounces at cs.uiuc.edu>] On Behalf Of Nico Weber
Sent: Friday, May 08, 2015 4:36 PM
To: reviews+D9208+public+0ac91376ffbd3e34 at reviews.llvm.org<mailto:reviews%2BD9208%2Bpublic%2B0ac91376ffbd3e34 at reviews.llvm.org>
Cc: cfe-commits at cs.uiuc.edu<mailto:cfe-commits at cs.uiuc.edu>
Subject: Re: [PATCH] Fix dependency file escaping

On Fri, May 8, 2015 at 4:01 PM, Paul Robinson <Paul_Robinson at playstation.sony.com<mailto:Paul_Robinson at playstation.sony.com>> 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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