CODEWITHSUNDEEP
scons
barjak
barjak

Reputation: 11270

How to tell SCons to stop computing implicit dependencies in a particular directory?

My SCons project depends on a lot of third party libs, each providing dozens or hundreds of include files.

My understanding of how SCons works is that, on each build, it parses the source files of my project to find the #include directives, and it uses the value of env['CPPPATH'] to find these files and compute their md5 sum.

This scanning is costly, and thus I would like to optimize this process by teaching SCons that all the headers of my third party files will never change. This property is actually enforced by the tool that manages our third party libs.

I know there is a --implicit-deps-unchanged option that forces scons to assume that the implicit dependencies did not change, but it works globally. I did not find a way to restrict this option to a particular directory. I tried to find if the default Scanner of implicit C++ files can be configured, but found nothing. I think it is possible to avoid using CPPPATH, and instead only give the -I option to the compiler directly, but it is cumbersome.

Is there any way to optimize SCons by teaching him that files in a directory will never, ever change?

Upvotes: 0

Views: 311

Answers (1)

bdbaddog
bdbaddog

Reputation: 3509

You can try pre-expanding the list of header file paths into CCFLAGS. Note that doing so means they will not be scanned.

for i in list_of_third_party_header_directories: 
  env['CCFLAGS'].append('-I' + i)

In this case the contents of CPPPATH would be your source directories, and not the third-party ones which you assert don't change.

Note that changing the command line of your compile commands in any way (unless the arguments are enclosed in $( $)) will cause your source files to recompile.

Upvotes: 1

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