Sphinx build make mode creates empty directories for unknown targets/builders

[markkuriekkinen]

Subject: the new Sphinx build "make mode" creates empty directories under the build directory even when the builder argument refers to a non-existent builder

Problem

• Sphinx quickstart 1.6 generates a Makefile with the catch-all target that uses the Sphinx "make mode" for building
• make can not check if the given argument is sensible since anything hits the catch-all target
• The Sphinx make mode gives an error when the given builder is not found, however, an empty directory with the target name has already been created under the build directory
• The empty directory should not be created at all if the builder does not even exist

Procedure to reproduce the problem

make fake

Error logs / results

Running Sphinx v1.6.4
making output directory...
loading translations [en]... done

Sphinx error:
Builder name fake not registered or available through entry point
Makefile:27: recipe for target 'fake' failed
make: *** [fake] Error 1

Sphinx gives an error that the fake builder does not exist, but nonetheless, an empty directory fake has been created under the build directory.

Expected results

The Sphinx make mode should not create empty directories for unknown builders.

Environment info

• OS: Ubuntu Linux 16.04
• Python 3.5.2
• Sphinx version: 1.6.4
• GNU Make 4.1

[tk0miya]

Fixed by #4389
Thank you for reporting!