bug in sage's Cython dependency tracker

[sagetrac-cwitty]

To reproduce: Start with Sage 3.4. Apply the attached patch (dependency-tracker-bug-testcase.patch). Rebuild with "sage -b", then run Sage. Type:

sage: import sage.rings.polynomial.real_roots

You will get an error:

TypeError: sage.rings.real_mpfi.RealIntervalField is not a type object

But if you touch real_roots.pyx and rebuild, the error goes away.

So somehow real_roots.pyx depends on real_mpfi.pyx in a way that the dependency tracker doesn't catch. (It's not obvious how, because real_roots.pyx never even mentions mpfi.)

Component: build

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/5545

[jdemeyer]

comment:1

Attachment: dependency-tracker-bug-testcase.patch.gz

[jdemeyer]

comment:5

worksforme:

jdemeyer@tamiyo:/usr/local/src/sage-git$ touch src/sage/rings/real_mpfi.pxd
jdemeyer@tamiyo:/usr/local/src/sage-git$ ./sage -b
scons: `install' is up to date.
Updating Cython code....
Enabling Cython debugging support
Compiling sage/rings/complex_interval.pyx because it depends on ./sage/rings/real_mpfi.pxd.
Compiling sage/rings/real_mpfi.pyx because it depends on sage/rings/real_mpfi.pxd.
Compiling sage/rings/polynomial/real_roots.pyx because it depends on ./sage/rings/real_mpfi.pxd.
[...]