Issue with "make distcheck" in GNU autotools project relating to generating a manual

I'm using autoconf and automake to build a tiny project. For the project's manual, I've used OpenBSD's native [mdoc format](http://man.openbsd.org/mdoc) , and the installable man-formatted manual is generated from this using [the mandoc utility](http://man.openbsd.org/mdoc) . The man-formatted manual will be installed as the actual manual with make install, as some systems do not grok mdoc properly, or at all. In the project's doc directory, I have a Makefile.am file that currently looks like the following (the manual is for a utility called shell): dist_man1_MANS= shell.man EXTRA_DIST= shell.mdoc shell.man: shell.mdoc $(mandoc) -T man shell.mdoc >shell.man $(mandoc) will be properly expanded to the full path of the mandoc formatter (this variable is set by the configure script). This allows me to run make dist which creates shell.man and then creates a compressed tar archive containing both the source mdoc manual and the generated man manual along with the rest of the project's distribution files: $ tar tzf shell-toolbox-20180401.tar.gz ... shell-toolbox-20180401/doc/Makefile.am shell-toolbox-20180401/doc/shell.man shell-toolbox-20180401/doc/Makefile.in shell-toolbox-20180401/doc/shell.mdoc This tar archive can later be used to successfully build and install the project, and its manual. So far so good. However, if I run [make distcheck](http://www.gnu.org/software/automake/manual/html_node/Checking-the-Distribution.html) (because I'd like to make sure it absolutely positively works): $ make distcheck ... checking for a BSD-compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for a thread-safe mkdir -p... /usr/local/bin/gmkdir -p checking for gawk... gawk checking whether make sets $(MAKE)... yes checking whether make supports nested variables... yes checking for mandoc... /usr/bin/mandoc checking that generated files are newer than configure... done configure: creating ./config.status config.status: creating Makefile config.status: creating src/Makefile config.status: creating doc/Makefile config.status: creating src/shell Making all in src Making all in doc /usr/bin/mandoc -T man shell.mdoc >shell.man mandoc: shell.mdoc: ERROR: No such file or directory *** Error 3 in shell-toolbox-20180401/_build/sub/doc (Makefile:459 'shell.man') *** Error 1 in shell-toolbox-20180401/_build/sub (Makefile:345 'all-recursive') *** Error 1 in /home/myself/local/build/shell-toolbox (Makefile:576 'distcheck') It seems as if the source mdoc file is not available in the build directory when the manual needs to be built: $ ls shell-toolbox-20180401/_build/sub/doc total 32 -rw-r--r-- 1 myself myself 14989 Apr 1 21:35 Makefile -rw-r--r-- 1 myself myself 0 Apr 1 21:35 shell.man The zero-length shell.man file comes from the failed mandoc run. The source is available in the unpacked archive, but just not copied over to the _build/sub/doc directory: $ ls -l shell-toolbox-20180401/doc total 48 -r--r--r-- 1 myself myself 178 Apr 1 21:23 Makefile.am -r--r--r-- 1 myself myself 13925 Apr 1 21:23 Makefile.in -r--r--r-- 1 myself myself 3443 Apr 1 21:27 shell.man -r--r--r-- 1 myself myself 3319 Apr 1 18:54 shell.mdoc **Question**: What automake magic do I have to apply to get make distcheck to properly copy the mdoc source to the build directory before it attempts to generate the man-formatted manual? I'm looking for a "proper" way of doing this, not a hack. I tried using man1_SOURCES= shell.mdoc but that makes automake complain with doc/Makefile.am:2: warning: variable 'man1_SOURCES' is defined but no program or doc/Makefile.am:2: library has 'man1' as canonical name (possible typo) --- Another way to provoke this error is to manually do a [VPATH build](http://www.gnu.org/software/automake/manual/html_node/VPATH-Builds.html) (which is basically what's happening when doing make distcheck): $ make distclean $ mkdir t $ cd t $ ../configure checking for a BSD-compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking for a thread-safe mkdir -p... /usr/local/bin/gmkdir -p checking for gawk... gawk checking whether make sets $(MAKE)... yes checking whether make supports nested variables... yes checking for mandoc... /usr/bin/mandoc checking that generated files are newer than configure... done configure: creating ./config.status config.status: creating Makefile config.status: creating src/Makefile config.status: creating doc/Makefile config.status: creating src/shell $ make Making all in src Making all in doc /usr/bin/mandoc -T man shell.mdoc >shell.man mandoc: shell.mdoc: ERROR: No such file or directory *** Error 3 in doc (Makefile:459 'shell.man') *** Error 1 in /home/myself/local/build/shell-toolbox/t (Makefile:345 'all-recursive') $ ls -l doc total 32 -rw-r--r-- 1 myself myself 14589 Apr 1 22:42 Makefile -rw-r--r-- 1 myself myself 0 Apr 1 22:42 shell.man