[Scons-users] 2.5.0 scanner fidelity regression since 2.3.4

[Bill Deegan]

Dave,

The question is how to instruct SCons that the command doesn't need
scanning?
So while cp doesn't need such, it's possible that others would.

-Bill

On Fri, Mar 17, 2017 at 1:24 PM, Dave Vitek <dvitek at grammatech.com> wrote:

> On 3/16/2017 10:20 PM, William Blevins wrote:
>
> Dave,
>
> I'm not sure I understand how you came to your conclusion. The SCons
> Command Builder takes 3 parameters: a source, a target, and a command
> string (http://scons.org/doc/HTML/scons-user.html#chap-builders-commands)
> Even if the command string is empty, the Command Builder creates an
> explicit dependency as "target" depends on "source". SCons cannot be
> scanning "test2.h" in your example because "test2.h" never exists;
> therefore, it has no contents to be scanned nor an implicit dependencies to
> be created. In your example, that means "test2.h" depends on "test.h":
>
> Command('test2.h', 'test.h', 'echo "" > test2.h')
>>
>
> File "test.h" depends on "test2.h" implicitly via the contents of "test.h"
> via dependency scanning (as it should):
>
> // test.h
>> #include "test2.h"
>
>
>
> I disagree with the phrase "as it should."  Let's simplify the example
> even further to just this, and absolutely *nothing* else in the SConstruct:
>
> Command('test2.h', 'test.h', 'cp $SOURCE $TARGET')
>
> I think you would be hard pressed to say that there is anything wrong with
> this rule.  I am trying to make a copy of a file.  I should not get a
> different dependence tree just because of the file's extension.  The "cp"
> command itself certainly does not behave differently with different file
> extensions.  The "cp" command definitely does not need the destination file
> to exist to succeed, which is what SCons seems to think.
>
> - Dave
>
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