Using CMake + Ninja to download dependencies using GIT

Question

I have an ExternalProject dependency that gets cloned (using git) in the build process. This all works great with CMake + Make.

mkdir build && cd build; 
cmake ..
make

It correctly clones and builds the library using git when I type make.

However, when I use the Ninja Generator:

mkdir build && cd build; 
cmake -GNinja ..
ninja

I get the following error:

$ cmake -GNinja ..                                                                                                                                                                                                                                                   -- The C compiler identification is AppleClang 6.0.0.6000054
-- The CXX compiler identification is AppleClang 6.0.0.6000054
-- Check for working C compiler using: Ninja
-- Check for working C compiler using: Ninja -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler using: Ninja
-- Check for working CXX compiler using: Ninja -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Boost version: 1.56.0
-- Found the following Boost libraries:
--   unit_test_framework
-- Found Git: /usr/local/bin/git (found version "2.1.2")
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/carneiro/src/gamgee/build


$ ninja
ninja: error: 'contrib/htslib-prefix/src/htslib/libhts.a', needed by 'test/gamgee_test', missing and no known rule to make it

Is git downloading of external projects not supported by the cmake+ninja combo?

Answer 1

Turns out if you do a clean before building, it all works and ninja does download my dependencies correctly.

So the workflow looks like this:

mkdir build && cd build
cmake -G Ninja ..
ninja clean  # if you don't do this, it will not download Externalproject dependencies
ninja

Must be some kind of bug in the Ninja generator, but I'm happy with this workflow for now.