RFR: JDK-8244844 javac command line is not re-executable

[Erik Joelsson]

On 2020-05-12 10:08, Magnus Ihse Bursie wrote:
> On 2020-05-12 17:38, Erik Joelsson wrote:
>> On 2020-05-12 08:29, Magnus Ihse Bursie wrote:
>>> We've broken our golden rule in SetupJavaCompilation, that all 
>>> command lines should be copy/paste:able to re-execute them from the 
>>> command line. The reason is that the file containing the source code 
>>> file names has a temporary name, which is renamed after the 
>>> compilation. This is just a messy way to use the file both as input 
>>> to javac and as a marker that the compilation has succeeded. By 
>>> splitting up these two roles, we get more readable code and a 
>>> re-executable command line.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8244844
>>> WebRev: 
>>> http://cr.openjdk.java.net/~ihse/JDK-8244844-make-javac-re-executable/webrev.01
>>>
>> I really like seeing this fixed, but not sure about this patch. By 
>> moving the filelist to a separate rule and only having the source 
>> files as prereq, there will be cases where the source files 
>> timestamps have not changed, but the list of files may have. I think 
>> this would be safely covered if you moved VARDEPS_FILE as prereq to 
>> FILELIST.
> I see your point. Will do that.
>
> I was also a bit divided about whether the actual javac invocation 
> rule should keep $$($1_SRCS) as a dependency. Technically, it's not 
> needed, since changes in the sources will result in the filelist being 
> updated, but maybe the intention will be better expressed. And if the 
> set of files has not changed, then we will write the same files back 
> to the filelist, which effectively just updates the timestamp in a 
> roundabout way. If we keep the list of source files as dependency, we 
> are free to implement a future optimization where the filelist is not 
> updated if the set of files has not changed.
>
> Otoh, I don't know if a huge list of dependencies (the number of 
> sources files for e.g. java.base is non-trivial!) affects make 
> performance, so listing it twice just to make it "look good" maybe 
> isn't a good idea.
>
> Do you have any opinion?
>
In general I like to list prereqs if they logically are direct prereqs. 
The sources are used as input in the compilation recipe, so that would 
be a direct prereq. If a prereq is really only transitive, then I don't 
want to list it. I don't know what the performance impact would be, I'm 
guessing it's not even measurable, but if it is, then maybe save some 
processing by not adding the sources to both rules. No strong opinion in 
this case.

/Erik

> /Magnus
>>
>> /Erik
>>
>>
>