RFR: JDK-8189955 Configuration validation is broken for some types of paths

[Magnus Ihse Bursie]

On 2017-10-26 10:09, Erik Joelsson wrote:
> I see why this huge check becomes necessary for a valid comparison, 
> but it's quite a bit of extra complexity added as well. I was worried 
> about the extra overhead on an already slow platform so I took the 
> time to measure. While it's certainly measurable it's hardly 
> noticeable. On a fast machine, the difference is around 50-100ms on 
> repeated make invocations (baseline 1.85s). On my slow laptop it's 
> 300-400ms, but the baseline is already over 7 seconds so as said, 
> hardly noticeable.
The alternative is to drop the check entirely. I did some source control 
archeology now, to figure out the origin of this check. It has grown a 
bit over the years to handle more complex cases, but the original test 
was introduced by me in JDK-8076060, which was the big rewrite that 
created Init.gmk and the current "bootstrapping" process of the build.

I can't, at least now, figure out what was the driving need behind that 
check. It might been that I had collected some complaints about odd 
broken setups that "the build system should check for that!!! i've 
wasted hours!!!" but never got a separate bug. Or I might have 
encountered issues myself while developing the patch. Or I just thought 
it was prudent to check.

In any case, I think it's fully viable by now to remove the check in its 
entirety. Do you agree?

>
> That said, line 392 is easily expressible using the make filter 
> function instead of going to the shell. All the other shell calls seem 
> to be necessary however.
>
> Just thinking some more. Would it be possible to do something like "cd 
> DIR && pwd" for both dirs and just compare the output of that instead? 
> If that works it would seem like way fewer shell calls and simpler logic.
Unfortunately, that will not present a canonical representation of the 
directory. In cygwin, both /cygdrive/c/cygwin/home/user and /home/user 
is the same directory, but cygwin will not rewrite the path of any of 
them using that formula. :-( So for better or for worse, I think the 
method that has hardened over the years in our configure script is a 
battle-proven way to create a canonical path representation on all 
platforms.

/Magnus

>
> /Erik
>
>
> On 2017-10-25 17:03, Magnus Ihse Bursie wrote:
>> We are validating that the topdir we're using when running make is 
>> the same as when we were running configure.
>>
>> For some circumstances, most typically when using a subdirectory in 
>> the user's home directory (e.g. ~/jdk10) on Cygwin, this check fails.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8189955
>> WebRev: 
>> http://cr.openjdk.java.net/~ihse/JDK-8189955-configuration-validation-is-broken-for-some-paths/webrev.01
>>
>> /Magnus
>>
>