Question about escaping spaces in filenames in Cython dependencies file

[lesteve]

tl;dr

It seems like Cython dependencies file should escape the spaces in paths, otherwise ninja keeps building files.

I'd like to make sure my understanding is correct before potentially opening a PR in Cython to fix the behaviour.

It seems like I found at least a similar thing in rust-bindgen rust-lang/rust-bindgen#2503.

More details

I noticed this when working on #15219.

In meson root folder execute the following (which I think is what the tests are doing):

meson setup --wipe my-build test\ cases/cython/2\ generated\ sources 
ninja -C my-build

This builds as expected.

The suprising thing is that rerunning ninja rebuilds some already built files, see -d explain output below (you can tell that there are issues related to spaces):

❯ ninja -C my-build -d explain
ninja: Entering directory `my-build'
ninja explain: ../test is dirty
ninja explain: cases/cython/2 is dirty
ninja explain: generated is dirty
ninja explain: sources/simpleinclude.pyx is dirty
ninja explain: sources/simplestuff.pxi is dirty
[0/3] Compiling Cython source '/home/lesteve/dev/meson/test cases/cython/2 generated sources/simpleinclude.pyx'
ninja explain: ../test is dirty
ninja explain: cases/cython/2 is dirty
ninja explain: generated is dirty
ninja explain: sources/simpleinclude.pyx is dirty
ninja explain: sources/simplestuff.pxi is dirty
[1/3] Compiling Cython source '/home/lesteve/dev/meson/test cases/cython/2 generated sources/simpleinclude.pyx'
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c is dirty
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c is dirty
[1/3] Compiling C object simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/meson-generated_simpleinclude.pyx.c.o
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c is dirty
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c is dirty
[2/3] Compiling C object simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/meson-generated_simpleinclude.pyx.c.o
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/meson-generated_simpleinclude.pyx.c.o is dirty
[2/3] Linking target simpleinclude.cpython-314t-x86_64-linux-gnu.so
ninja explain: simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/meson-generated_simpleinclude.pyx.c.o is dirty
[3/3] Linking target simpleinclude.cpython-314t-x86_64-linux-gnu.so

One of the dependency file has spaces in paths:

cat my-build/simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c.dep

simpleinclude.cpython-314t-x86_64-linux-gnu.so.p/simpleinclude.pyx.c: \
  ../test cases/cython/2 generated sources/simpleinclude.pyx \
  ../test cases/cython/2 generated sources/simplestuff.pxi

If I edit manually the file to espace spaces with \, I get the expected behaviour ninja: no work to do.

[lesteve]

Maybe @eli-schwartz or @rgommers, you have some insights into escaping spaces inside paths in dependency files?

[rgommers]

Spaces needing escaping looks correct to me. There is no formal spec for depfiles, so whatever works here. The other potential hiccup is backslashes on Windows, which apparently might need escaping (a one-off test on a Windows machine will tell).

[eli-schwartz]

Effectively the spec is "it works as a makefile fragment, so check if it's GNU Make syntax".

[lesteve]

OK thanks for your insights, I'll try to do a PR in Cython to take them into account!